RESOURCE UTILIZATION FOR EFFICIENT CROP PRODUCTION SYSTEMS IN THE MIDSOUTH

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0201150
• Project No.: ARK02029
• Project Start Date: Oct 1, 2010
• Project End Date: Sep 30, 2015

Project Director
Purcell, L.

Recipient Organization
UNIVERSITY OF ARKANSAS
(N/A)
FAYETTEVILLE,AR 72703

Performing Department
Crop, Soil & Environmental Sciences

Non Technical Summary
Agriculture is a key industry for the economic prosperity for Arkansas. Five major grain crops are grown on approximately 2.26 million ha each year in Arkansas with an estimated annual value of $2.84 billion. With the exception of soybean, yields of these crops in Arkansas are very close to, or exceed, average national yields (Table 1). Although crop yields for Arkansas are generally close to the national average, these yields for soybean, corn, grain sorghum, and wheat are approximately one-half of their yield under optimum conditions. In the absence of biotic limitations (such as pathogens), there are four essential resources required for crop growth and yield: (1) an adequate water and (2) nutrient supply, (3) solar radiation to drive photosynthetic processes, and (4) adequate time during a growing season (frost-free for warm-season crops) for plant development. The primary limitation for yield of soybean, corn, and grain sorghum is adequate and timely water availability. The most obvious method of increasing yield under water-limited conditions is to irrigate, and, indeed irrigation is an important aspect of Arkansas crop production systems. For soybean, 75% of the crop is irrigated and yield due to irrigation usually ranges 30 to 50% over the nonirrigated crop. Although statistical data are not available for corn and grain sorghum crops in Arkansas, similar yield responses to irrigation would be expected. Despite obvious yield benefits, irrigation may be limited by initial costs of investment, pumping facilities, aquifer depth, quality of water, and competition of irrigation water by other crops. Therefore, there is a need to develop management systems and genetic resources that can efficiently utilize irrigation and rainfall resources for crop production. Genetic variability for all of the five major grain crops listed in Table 1 are great. Our current breeding, management, and Extension programs at the University of Arkansas are focused on using genetic resources that fit well within current management systems. Extending the germplasm pool that we use in Arkansas may be accomplished in two ways. First, high-yielding cultivars (or hybrids) may be available from other regions that can be used effectively in Arkansas for increasing utilization of specific resources. For example, using short-season crops from the northern U.S. may enable farmers in the Midsouthern U.S. to avoid late-season drought. Secondly, specific traits may be available in germplasm collections that when combined with adapted, high-yielding cultivars (or hybrids) would provide increased efficiency in resource utilization.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
111	1820	1020	25%
203	1820	1020	25%
203	1820	1080	25%
206	1899	1020	25%

Knowledge Area
206 - Basic Plant Biology; 111 - Conservation and Efficient Use of Water; 203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants;

Subject Of Investigation
1820 - Soybean; 1899 - Oilseed and oil crops, general/other;

Field Of Science
1080 - Genetics; 1020 - Physiology;

Keywords

physiological and genetic characterization

resources crop production

Goals / Objectives
A. Characterize crop yield responses to water, solar radiation, and nutritional resources under non-limiting and limiting conditions. B. Characterize genetic traits in soybean for their ability to utilize efficiently nutrients, solar radiation, and water resources.

Project Methods
Characterize crop yield responses to water, solar radiation, and nutritional resources under non-limiting and limiting conditions. Crop responses to resource availability will be evaluated directly in field experiments and through relatively simple, mechanistic crop simulation models (Sinclair, 1986). The premise for our field research is that in the absence of any biotic limitation, the ideal environment for crop production is limited only by the amount of solar radiation received during the growing season. Beginning first with soybean, we will evaluate yield response to plant nutrients required in the greatest amounts. Large amounts of poultry manure will be applied the fall prior to sowing soybean, and lime and nutrients will be applied to meet soil-test recommendations. Soybean from a wide range of maturity groups will be seeded in mid April in 40-cm rows at populations of approximately 35 m. After emergence, solar radiation intercepted will be measured twice per week until full canopy closure to allow determination of CIPAR. All experiments will be irrigated by overhead sprinklers when the estimated soil-moisture deficit reaches 25 mm. Half the field will be supplied fertilizer through the irrigation system while the other half will receive only water. At approximately weekly intervals, nitrogen will be added at relatively low concentrations. Potassium, sulphur, magnesium, and micronutrients will be added periodically. Leaf tissue will be collected from all plots each week at beginning seed fill and analyzed for macro and micro nutrients. The second step in the modeling approach is to determine whether or not a crop will likely receive the necessary resources of solar radiation and rainfall in a given region and with a given production scenario. Essential factors that will be considered include crop maturity, sowing date, location, and whether or not the crop will be irrigated or rain fed. These models predict daily responses for crop growth and development as functions of water, light, and temperature from the historical weather data that will be collected. Yield responses for each year are predicted based upon the given scenarios of crop maturity, sowing date, location, and irrigation, and the results from each year essentially serve as a replicate for a given experimental scenario. The use of the long-term weather data can then be used to evaluate the risk of an associated production practice using environmental conditions that occur at a particular location. Characterize genetic traits in soybean for their ability to utilize efficiently solar radiation and water resources. The research approach described for Objective A will provide important information about how crops can be managed, using currently available cultivars and hybrids, for maximizing production with given amounts of water and solar radiation resources. Research described for Objective B will explore genetic traits that may, perhaps, extend the ability of currently used germplasm to utilize these resources. The focus of this objective will be on genetic traits in soybean that may be important for increasing drought tolerance or increasing light utilization.

Progress 10/01/10 to 09/30/15

Outputs
Target Audience:Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?During the course of this project, there have been training opportunities for eight graduate students, three visiting scholars, two postdoctoral associates and six undergraduate students. Activities for the graduate students and postdocs have included annual trips to the American Society of Agronomy meetings, the Soybean Breeder's Workshop, and presentations at regional and state meetings where they have made presentations and participated in discussions. Students, visiting scholars, and postdocs have attended field demonstrations and tours during the course of the project. Training opportunities have also included hands-on activities and measurements of crop performance, measurement techniques, irrigation methods, and statistical procedures. How have the results been disseminated to communities of interest?Information from this project have been widely disseminated to the scientific community through 23 peer-reviewed manuscripts, 29 national or international presentations, 42 regional or state presentations, and 1 book chapter. Additionally, numerous popular press presentations have focused on my research efforts and several videos on youtube.com have featured my research activities. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The ability of a crop to reach its potential yield depends upon the availability of the primary resources necessary for crop growth (solar radiation or light energy, water, and nutrients) and the ability to use these resources efficiently. Research in this project evaluated soybean potential yield and crop growth characteristics under conditions when these resources were optimized. Although we cannot control the incident solar radiation on a given day, we were able to manage the quantity of solar radiation that our crop received by selecting an appropriate planting date, by choosing cultivars that develop and mature during an advantageous portion of the growing season, and by selecting a row spacing and population density that intercepts an optimum amount of solar radiation. We optimized the amount of water available in our experiment by proper irrigation and ensuring that the crop had adequate surface and/or internal drainage. To ensure that nutrients were not limiting soybean potential yield, we applied large amounts of poultry litter and twice the amount of nutrients recommended based upon soil-test recommendations, and we applied fertilizer through the irrigation system during the seed-filling period. By optimizing these conditions our measurements defining crop growth characteristics (crop growth rate, radiation use efficiency, and N accumulation rate) were substantially greater than any values reported previously in the literature. Soybean yields (7953 kg ha-1 or 118.5 bushels acre-1) were also among the greatest ever reported in peer-reviewed publications. The mid-southern US has a wide planting window for soybean that extends from mid-March to mid-July for soybean that is double-cropped after wheat. This region also grows soybean MGs from MG 3 through MG 6. Although it is widely recognized that cultivar and MG selection is one of the most important determinants of crop yield, little information is available to identify the best MG selection for a given planting date across the range of latitudes between 29 and 39oN. To address this question we conducted a large regional experiment at 10 locations in the Midsouth with locations ranging from College Station, Texas to Columbia, Missouri. We evaluated yield response under irrigation for four planting dates (early spring to early summer), four MGs (3, 4, 5, and 6), and four varieties within each MG for three years. These results provide clear documentation of the most productive MG to plant for a given date across a wide range of locations. For example, for all MGs, the first two planting dates had higher yields than the last two planting dates. For early planting, MGs 4 and 5 out performed earlier and later MGs, but for late planting dates MG 4 cultivars were the best choice. From this information, a production guide has been developed for Arkansas, and guides for other locations are in development. The primary resource limiting soybean yield throughout the Midsouth and the US is the availability of adequate soil moisture. We have identified soybean genotypes that have high water use efficiency and molecular markers that can be used as tags for genes associated with water use efficiency. Two traits that we have focused considerable attention on are the ability to prolong nitrogen fixation during drought and delayed symptoms of wilting during drought. By carefully screening hundreds of genotypes and breeding lines, we have identified molecular markers for both of these traits, and this information is being used to transfer the genes responsible for these traits into high-yielding, adapted cultivars. The delayed-canopy-wilting trait and the prolonged-nitrogen-fixation trait have been evaluated with a crop simulation model that predicts yield using 50 years of weather data from across the US (Agron. J. 102:475-482). This analysis indicated that when yields were near the median for Arkansas that incorporating the delayed-wilting trait would increase yields about 400 kg ha-1 (6 bushels ac-1) and that the prolonged-nitrogen-fixation trait would increase yields about 1300 kg ha-1 (19 bushels ac-1). Using these estimates as the value of the traits from my research, the economic impact just for Arkansas, assuming a soybean price of $10 bu-1, is $69 million (delayed wilting) to $218 million (prolonged nitrogen fixation) per year.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Parvej, M.R.*, N.A. Slaton, L.C. Purcell, and T.L. Roberts. 2015. Potassium fertility effects yield components and seed potassium concentration of determinate and indeterminate soybean. Agron. J. 107:943-950.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Jacobs, A., K.R. Brye*, R. King, J. Douglas, L.S. Wood, L.C. Purcell, and M. Looper. 2015. Switchgrass management practice effects on near-surface soil properties in west-central Arkansas. Open J. Soil Sci. 5:69-86.
• Type: Journal Articles Status: Accepted Year Published: 2015 Citation: Dhanapal, A.P., J.D. Ray, S.K. Singh, V.H. Villegas, J.R. Smith, L.C. Purcell, C.A. King , P.B. Cregan, Q. Song, F.B. Fritschi*. 2015. Genome-wide association analysis of diverse soybean genotypes reveals novel markers for nitrogen derived from atmosphere (NDFA), nitrogen concentration ([N]), and C/N ratio. Plant Genome 8(3):1-15.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Salmeron, M. , E.E. Gbur, F.M. Bourland, L. Earnest, B.R. Golden, and L.C. Purcell*. 2015. Soybean maturity group choices for maximizing radiation interception across planting dates in the US Midsouth. Agron. J. 107:2132-2142.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Van Roekel, R.J. , L.C. Purcell*, and M. Salmeron . 2015. Physiological and management factors contributing to soybean potential yield. Field Crops Res. 182:86-97.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Hwang, S. , C.A. King , J.D. Ray, P.B. Cregan, P. Chen, T.E. Carter, Jr., Z. Li, H. Abdel-Haleem, K.W. Matson, W. Schapaugh, Jr., and L.C. Purcell*. 2015. Confirmation of delayed canopy wilting QTLs from multiple soybean mapping populations. Theor. Appl. Genet. 128:2047-2065.
• Type: Journal Articles Status: Accepted Year Published: 2015 Citation: Ray, J.D.*, A.P. Dhanapal, S.K. Singh, V. Hoyos-Villegas, J.R. Smith, L.C. Purcell, C.A. King , D. Boykin, P.B. Cregan, Q. Song, F.B. Fritschi. 2015. Genome-wide association study (GWAS) of ureide concentration in diverse maturity group IV soybean [Glycine max (L.) Merr.] accessions. G3 Genes Genom. Genet. 5: doi:10.1534/g3.115.021774.
• Type: Journal Articles Status: Accepted Year Published: 2015 Citation: Dhanapal, A.P., J.D. Ray, S.K. Singh, V. Hoyos-Villegas, J.R. Smith, L.C. Purcell, C.A. King , F.B. Fritschi*. 2015. Association mapping of total carotenoids in diverse soybean [Glycine max (L.) Merr.] genotypes based on leaf extracts and high-throughput canopy spectral reflectance measurements. Plos One 10(9): e0137213.doi:10.1371/journal.pone.0137213.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Wegerer, R., M. Popp*, X. Hu , and L.C. Purcell. 2015. Soybean maturity group selection: Irrigation and nitrogen fixation effects on returns. Field Crops Res. 180:1-9.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2016 Citation: Wegerer, R., M. Popp*, X. Hu , L.C. Purcell. 2016. Economic implications of soybean maturity group on herbicide program and irrigation needs. Crop Forage Turfgrass Manage. (in press).
• Type: Journal Articles Status: Awaiting Publication Year Published: 2016 Citation: Parvej, M.R.*, N.A. Slaton, L.C. Purcell, and T.L. Roberts. 2016. Soybean yield components and seed potassium concentration responses among nodes to potassium fertility. Agron. J. (in press).
• Type: Journal Articles Status: Awaiting Publication Year Published: 2016 Citation: Kawasaki, Y., Y. Tanaka, K. Katsura, L.C. Purcell, and T. Shiraiwa*. 2016. Yield and dry matter productivity of Japanese and US soybean cultivars. Plant Prod. Sci. (in press).
• Type: Journal Articles Status: Awaiting Publication Year Published: 2016 Citation: Salmeron, M.H, Gbur, E.E., Bourland, F.M., Buehring, N.W., Earnest, L., Fritschi, F.B., Golden, B.R., Hathcoat, D., Lofton, J., Miller, T.D., Neely, C., Shannon, G., Udeigwe, T.K., Verbree, D.A., Vories, E.D., Wiebold, W.J., and L.C. Purcell*. 2016. Yield response to planting date among soybean maturity groups for irrigated production in the US Midsouth. Crop Sci. (in press).
• Type: Book Chapters Status: Awaiting Publication Year Published: 2016 Citation: Bai, H. , L.C. Purcell*, and V. Skinner. 2016. High throughput phenotypic evaluation of drought-related traits in soybean. In: T. Kirkpatrick, L.C. Purcell, T. Roberts, and J. Ross (eds). Arkansas Soybean Research Series 2015. University of Arkansas Agricultural Experiment Station Research Series. (in press).
• Type: Book Chapters Status: Awaiting Publication Year Published: 2016 Citation: Adams, T.C., K.R. Brye*, L.C. Purcell, and J. Ross. 2016. Preliminary evaluation of soil property differences between high- and average-yielding soybean fields throughout Arkansas. In: T. Kirkpatrick, L.C. Purcell, T. Roberts, and J. Ross (eds). Arkansas Soybean Research Series 2015. University of Arkansas Agricultural Experiment Station Research Series. (in press).
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Kaler, A.S. , L.C. Purcell, A.P. Dhanapal, J.D. Ray, and F.B. Fritschi. 2015. Genome-wide association analysis of carbon isotope and oxygen isotope ratios in diverse soybean [Glycine max (L.)] genotypes. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Bai, H. , and L.C. Purcell. 2015. High throughput phenotypic evaluation of drought-related traits in soybean. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Salmeron, M. , E.E. Gbur, F.M. Bourland, N.W. Buehring, L. Earnest, F.B. Fritschi, B.R. Golden, D. Hathcoat, J. Lofton, A. McClure, T.D. Miller, C.B. Neely, G. Shannon, T.K. Udeigwe, D. Verbree, E.D. Vories, W.J. Wiebold, and L.C. Purcell. 2015. Yield response to planting date among soybean maturity groups for irrigated production in the Midsouth. 2015. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Dhanapal, A.P., J.D. Ray, S.K. Singh, V. Hoyos-Villegas, J.R. Smith, L.C. Purcell, C.A. King , and F.B. Fritschi. 2015. Identification of putative genomic loci for total chlorophyll in soybean using leaf extracts and high throughput spectral reflectance approaches. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Parvej, M.R., N.A. Slaton, M.S. Fryer, T.L. Roberts, L.C. Purcell, and R.E. DeLong. 2015. Post-season diagnosis of potassium deficiency in soybean using seed potassium concentration. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Parvej, M.R., N.A. Slaton, T.L. Roberts, L.C. Purcell, R.E. DeLong, and M.S. Fryer. 2015. Critical trifoliolate leaf and petiole potassium concentrations for soybean beyond the R2 growth stage. 2015. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Parvej, M.R., N.A. Slaton, T.L. Roberts, L.C. Purcell, R.E. DeLong, and M.S. Fryer. 2015. In-season diagnosis of potassium deficiency in soybean using leaf and petiole potassium concentrations. American Society of Agronomy annual meetings, Minneapolis, MN.
• Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Van Roekel, R.J. 2015. Physiological and nutritional characterization of high yield soybean. PhD Dissertation, University of Arkansas, Fayetteville.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? * During the past year, three PhD students have made substantial progress on their PhD research, and one student is finalizing his MS research. * Two postdoctoral associates are working with me on various projects. * Students and postdocs made presentations at national, regional, and state scientific meetings. How have the results been disseminated to communities of interest? * scientific, peer-reviewed manuscripts * presentations at scientific meetings and at farmer/producer meetings * webinars and internet interviews * trade magazine articles and interviews What do you plan to do during the next reporting period to accomplish the goals? During the next reporting cycle, research will continue characterizing crop yield responses to water, solar radiation, and nutritional resources under non-limiting and limiting conditions. Likewise, experiments will also characterize genetic traits in soybean for their ability to utilize efficiently nutrients, solar radiation, and water resources. Results will be reported in the scientific literature and will be dissiminated at scientific meetings and meetings targeted for farmers and producers.

Impacts
What was accomplished under these goals? A. Characterize crop yield responses to water, solar radiation, and nutritional resources under non-limiting and limiting conditions. Average soybean yield in Arkansas is around 2900 kg ha-1 (43 bushels acre-1) but yields up to 10,800 kg ha-1 (161 bushels acre-1) have been reported by a farmer in southwest Missouri competing in a yield contest. Our current scientific understanding of crop growth, nutrition, and agronomy would indicate that yields of this magnitude are not theoretically possible. The farmer who had reported these exceptional yields agreed to allow our research group on his farm over 3 years to make key measurements of yield, crop growth, and nutrition that could explain how these yield levels were possible. Key measurements included radiation use efficiency (RUE), which is a long-term measure of photosynthesis, and nitrogen accumulation rate (NAR). The yield levels over the 3-year period ranged from 6979 to 7953 kg ha-1 (104 to 119 bushels acre-1) and were substantially less than yields previous reported in yield contests at this location. Measurements of RUE and NAR, however, were larger than any values previously reported in the literature. In fact, RUE and NAR in 2013 were approximately 2-fold and 3-fold greater than values typically reported for a high-yielding, well-managed crop, respectively. This research provides a reassessment of the yield capacity of soybean that can be used in crop models and in evaluating yield-limiting factors in production agriculture. The US Midsouth has a wide planting window for soybean but there is poor understanding of the maturity group (MG) choices that perform best under irrigated conditions as those planting dates change. A large regional experiment was conducted at 10 locations in the Midsouth with locations ranging from College Station, Texas to Columbia, Missouri. We evaluated yield response for four planting dates (early spring to early summer), four MGs (3, 4, 5, and 6), and four varieties within each MG for two years. There was a clear yield advantage for planting early (prior to June) compared with planting late (after June) for all MGs. For the early planting dates, yields were greatest for MGs 4 and 5. For late planting dates, yields were greatest for late-MG 3 varieties and MG 4 varieties. These results call into question current recommendations that MG 5 and 6 varieties should be used for late planting dates and support recommendations for MG 4 varieties for early planting in the Midsouth. B. Characterize genetic traits in soybean for their ability to utilize efficiently nutrients, solar radiation, and water resources. A primary constraint for soybean production is drought stress, and the sensitivity of nitrogen fixation to drought limits productivity. There are differences among genotypes in the sensitivity of nitrogen fixation to drought, but the trait is difficult to evaluate and is rare among genotypes. Our previous research discovered that the ability to prolong nitrogen fixation under drought among different genotypes was closely associated with having low shoot nitrogen concentration. We selected 175 maturity group 4 accessions from the soybean germplasm collection that were genetically diverse, had relatively good yields and that were not prone to shattering or lodging. We evaluated these accessions in four irrigated environments for yield and shoot nitrogen concentration. Twelve accessions that were extremes for shoot nitrogen concentration and yield were further evaluated in a series of controlled-environment experiments for the ability to continue nitrogen fixation during drought. From these original 175 soybean accessions, two genotypes were found that prolonged nitrogen fixation during drought, and these genotypes had low shoot nitrogen concentration. These new sources of drought tolerance can now be used in a breeding program and the progeny screened for drought tolerant nitrogen fixation by measuring shoot nitrogen concentration. There is relatively little diversity in the US soybean germplasm and this is especially true with regards to traits conferring drought tolerance. One measurement that has been used successfully in wheat to increase drought tolerance is 13C-istope discrimination (CID), which is a surrogate measure of water use efficiency. We selected a group of 373 diverse, maturity group 4 accessions from the US soybean germplasm collection that had relatively good yield and agronomic performance. These accessions were grown for 2 years at both Columbia, MO and Stuttgart, AR under irrigated conditions. Shoot tissue was collected from these experiments and analyzed for CID. In addition, these accessions were genotyped with 12,347 SNP molecular markers. We identified chromosomal regions associated with low CID (high water use efficiency) using a genome-wide-association-study (GWAS) approach. We identified 39 SNPs that were significantly associated with CID in at least two environments. Of these 39 SNPs, 21 were associated with unique chromosomal regions. This is the first report of using GWAS in soybean for determining CID loci. The SNPs identified can now be used to confirm their utility in improving soybean performance under drought.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: King, C.A., L.C. Purcell, A. Bolton, J.E. Specht. 2014. A possible relationship between shoot N concentration and the sensitivity of N2 fixation to drought in soybean. Crop Sci. 54:746-756. Van Roekel, R.J, and L.C. Purcell. 2014. Soybean biomass and nitrogen accumulation rates and radiation use efficiency in a maximum yield environment. Crop Sci. 54:1189-1196. Salmeron, M., E.E. Gbur, F.M. Bourland, N.W. Buehring, L. Earnest, F.B. Fritschi, B.R. Golden, D. Hathcoat, J. Lofton, T.D. Miller, C. Neely, G. Shannon, T.K. Udeigwe, D.A. Verbree, E.D. Vories, W.J. Wiebold, and L.C. Purcell. 2014. Soybean maturity group choices for early- and late-plantings in the US Midsouth. Agron. J. 106:1893-1901. Dhanapal, A.P., J.D. Ray, S.K. Singh, V.H. Villegas, J.R. Smith, L.C. Purcell, C.A. King, P.B. Cregan, Q. Song, F.B. Fritschi. 2014. Genome-wide association study (GWAS) of carbon isotope ratio (?13C) in diverse soybean [Glycine max (L.) Merr.] genotypes. Theor. Appl. Genet. DOI 10.1007/s00122-014-2413-9.
• Type: Journal Articles Status: Accepted Year Published: 2015 Citation: Hwang, S., C.A. King, M.K. Davies, D.V. Charlson, J.D. Ray, P.B. Cregan, C.H. Sneller, P. Chen, T.E. Carter, Jr., and L.C. Purcell. 2015. Registration of the KS4895 x Jackson Mapping Population (AR93705). J. Plant Reg. (in press). Parvej, R., NA. Slaton, L.C. Purcell, and T.L. Roberts. 2015. Potassium availability effects on yield components and seed potassium concentration of determinate and indeterminate soybeans. Agron. J. (accepted pending revisions).
• Type: Journal Articles Status: Under Review Year Published: 2015 Citation: Van Roekel, R.J., and L.C. Purcell. Physiological and management factors contributing to soybean maximum yield. Field Crops Res. Dhanapal, A.P., J.D. Ray, S.K. Singh, V. Hoyos-Villegas, J. R. Smith, L.C. Purcell, C.A. King, F.B. Fritschi. 2015. Genome-wide association analysis of diverse soybean genotypes reveals novel markers for nitrogen derived from atmosphere (Ndfa), nitrogen concentration ([N]) and C/N ratio. Plant Genome. (in review). Jacobs, A.A., K.R. Brye, J.R. King, J.L. Douglas, L.S. Wood, M.L. Looper, and L.C. Purcell. Switchgrass cultivar, harvest frequency, fertilizer source, and irrigation effects on near-surface soil properties in west-central Arkansas. Soil Sci. (in review).
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2014 Citation: Clark, R. W.T. Schapaugh, Jr., J. Poland, L.C. Purcell, and C.A. King. Characterizing Drought Resistance in Soybean Using Spectral Reflectance Indices. ASA/CSSA annual meeting, 2-5 November 2014. Long Beach, CA. Salmeron, M., E.D. Gbur, F.M. Bourland, L. Earnest, B.R. Golden, and L.C. Purcell. Soybean maturity group and row spacing choices for maximizing light interception in the US Midsouth. ASA/CSSA annual meeting, 2-5 November 2014. Long Beach, CA. Bai, H. and L.C. Purcell. High throughput phenotypic evaluation of drought-related traits in soybean. ASA/CSSA annual meeting, 2-5 November 2014. Long Beach, CA. King, C.A. and L.C. Purcell. Evaluation of methods for determination of relative transpiration response to soil drying in container-grown plants. ASA/CSSA annual meeting, 2-5 November 2014. Long Beach, CA. Purcell, L.C. Nitrogen nutrition in soybean  Fertilization, fixation, and a paradox. ASA/CSSA annual meeting, 2-5 November 2014. Long Beach, CA. Rhezali A., L.C. Purcell, and T.L. Roberts. Characterization of a smartphone application to predict leaf N concentration in maize. ASA/CSSA annual meeting, 2-5 November 2014. Long Beach, CA. Purcell, L.C. and R.J. Van Roekel. Maximizing soybean yield: Genetics, nutrition, and management. CPM Short Course and MCPR Trade Show. 11 December 2014. Minneapolis, MN. Rhezali A., L.C. Purcell, and T.L. Roberts. Characterization of a smartphone application to predict leaf N concentration in maize. Arkansas Crop Protection Association Conference. 2-3 December 2014. Fayetteville, AR.

Progress 01/01/13 to 09/30/13

Outputs
Target Audience: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. Changes/Problems: There are no major changes/problems in the research plan or approach. What opportunities for training and professional development has the project provided? * During the past year, two MS students have completed their degrees, three students are continuing their PhD research, and one student is continuing his MS research. * Two postdoctoral associates are working with me on various projects. * Students and postdocs made presentations at national, regional, and state scientific meetings. How have the results been disseminated to communities of interest? Results have been disseminated through: * scientific, peer-reviewed manuscripts * presentations at scientific meetings and at farmer/producer meetings * webinars and internet interviews * trade magazine articles and interviews What do you plan to do during the next reporting period to accomplish the goals? During the next reporting cycle, research will continue characterizing crop yield responses to water, solar radiation, and nutritional resources under non-limiting and limiting conditions. Likewise, experiments will also characterize genetic traits in soybean for their ability to utilize efficiently nutrients, solar radiation, and water resources. Results will be reported in the scientific literature and will be dissiminated at scientific meetings and meetings targeted for farmers and producers.

Impacts
What was accomplished under these goals? A. Characterize crop yield responses to water, solar radiation, and nutritional resources under non-limiting and limiting conditions. *Experiments conducted at Kip Cullers' farm (who holds the record for the highest soybean yield) to measure crop growth characteristics in his yield-contest field. * Small-plot experiments, complimentary to those on Mr. Cullers' farm, were established at our Experiment Station to evaluate soybean growth response to solar radiation and plentiful nutrient supply under non-limiting conditions. * Strip trials were conducted on farmers' fields in Eastern Arkansas to determine if yield responses to obtain maximum yields observed in small-plot research would be effective at the field level. B. Characterize genetic traits in soybean for their ability to utilize efficiently nutrients, solar radiation, and water resources. * Three soybean recombinant inbred populations were evaluated in field experiments for one or more of the following traits: (1) delayed wilting under drought; (2) shoot ureide and nitrogen concentrations under well-watered and drought conditions; (3) carbon isotope discrimination as a surrogate measure of water use efficiency; (4) yield under well watered and drought conditions. These populations have been genotyped with molecular markers and we are using this information to identify QTLs associated with these traits. * A set of 373 diverse, maturity group 4 soybean accessions have been genotyped with approximately 12,000 SNPs with a minor allele frequency greater than 10%. These accessions were phenotyped under field conditions for delayed wilting under drought stress. We have also phenotyped this set of genotypes for ureide and nitrogen concentrations and for carbon isotope discrimination. We are mapping these traits using genome wide association studies.

Publications

• Type: Journal Articles Status: Published Year Published: 2013 Citation: Fritschi, F.B., J.D. Ray, L.C. Purcell, C.A. King, J.R. Smith, and D.V. Charlson. 2013. Diversity and implications of soybean stem nitrogen concentration. J. Plant Nutr.36:2111-2131. Hwang, S., C.A. King, M.K. Davies, J.D. Ray, P.B. Cregan, and L.C. Purcell. 2013. QTL analysis of shoot ureide and nitrogen concentrations in soybean [Glycine max (L.) Merr.]. Crop Sci. 53:2421-2433. Hwang, S., J.D. Ray, P.B. Cregan, C.A. King, M.K. Davies, and L.C. Purcell. 2014. Genetics and mapping of quantitative traits for nodule number, weight, and size in soybean (Glycine max L. [Merr.]). Euphytica. 195:419-434.
• Type: Journal Articles Status: Accepted Year Published: 2014 Citation: King, C.A., L.C. Purcell, A. Bolton, and J.E. Specht. 2013. A possible relationship between shoot N concentration and the sensitivity of N2 fixation to drought in soybean. Crop Sci. (in press). Van Roekel, R.J. and L.C. Purcell. 2014. Soybean biomass and nitrogen accumulation rates and radiation use efficiency in a maximum yield environment. Crop Sci. (accepted pending revision).
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Purcell, L.C. A. Bolton, C.A. King, J.D. Ray, F.B. Fritschi, A. Dhanapal, S. Hwang, and P.B. Cregan. Prolonged nitrogen fixation in soybean during drought: physiologic and genetic characterizations. North American Symbiotic Nitrogen Fixation Conference. 15 July 2013. Minneapolis, MN. Purcell, L.C., A. Bolton, C.A. King, J.D. Ray, F.B. Fritschi, A.P. Dhanapal, S. Hwang, and P.B. Cregan. Identifying Drought Tolerance in Soybean: From the Growth Chamber to the Field and Back Again. ASA/CSSA Annual Meeting. 3-6 November 2013. Tampa, Florida. Van Roekel, R.J. , L.C. Purcell, and D. Poston. Busting soybean yield barriers without breaking the bank. ASA/CSSA Annual Meeting. 3-6 November 2013. Tampa, Florida. Bai, H. and L.C. Purcell. High throughput phenotypic evaluation of drought-related traits in soybean. ASA/CSSA Annual Meeting. 3-6 November 2013. Tampa, Florida. Van Roekel, R.J., M. Salmeron, and L.C. Purcell. 2013. Physiological characterization and modeling of soybean in a maximum yield environment. ASA/CSSA Annual Meeting. 3-6 November 2013. Tampa, Florida. Salmer�n, M., L.C. Purcell, F.M. Bourland, N.W. Buehring, L. Earnest, E. Gbur, B.R. Golden, D. Hathcoat, J. Lofton, T.D. Miller, G. Shannon, T.K. Udeigwe, M. Wyss, and E.D. Vories. Stability of soybean yield and quality over a wide range of maturities and planting dates in the Midsouth. ASA/CSSA Annual Meeting. 3-6 November 2013. Tampa, Florida. Dhanapal, A.P., J.D. Ray, S.K. Singh, V. Hoyos-Villegas, J.R. Smith, L.C. Purcell, C.A. King, P.B. Cregan, and F.B. Fritschi*. Genome-wide association studies (GWAS) for shoot ureide concentration in diverse soybean genotypes. ASA/CSSA Annual Meeting. 3-6 November 2013. Tampa, Florida.
• Type: Theses/Dissertations Status: Published Year Published: 2013 Citation: Bolton, A. 2013. Selecting drought tolerant soybean genotypes using QTLs associated with shoot ureide and nitrogen concentrations. MS Thesis, University of Arkansas. Siddons, U. 2013. Dark green color index as a method of real-time in-season corn nitrogen measurement and fertilization. MS Thesis, University of Arkansas.
• Type: Websites Status: Published Year Published: 2013 Citation: University of Arkansas Cooperative Extension Service. 2013. Maximum Yield of Soybean Research Wrap-up. Soybean Podcasts [Online]. Available at http://www.aragriculture.org/crops/soybeans/podcasts/number152.htm. (Posted 11 Oct. 2013). University of Arkansas Cooperative Extension Service, Little Rock. University of Arkansas Cooperative Extension Service. 2013. How to Estimate Yield with Ryan Van Roekel. Soybean Podcasts [Online]. Available at http://www.aragriculture.org/crops/soybeans/podcasts/number148.htm. (Posted 22 Aug. 2013). University of Arkansas Cooperative Extension Service, Little Rock. University of Arkansas Cooperative Extension Service. 2013. Finding the maximum yield of soybeans. Soybean Podcasts [Online]. Available at http://www.aragriculture.org/crops/soybeans/podcasts/number143.htm. (Posted 13 June 2013). University of Arkansas Cooperative Extension Service, Little Rock.

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: Crop production is often limited by the timing and amount of rainfall and the ability to irrigate properly. Genetic differences among soybean cultivars offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Our research evaluating genetic differences in the response of soybean to drought was disseminated through presentations at the American Society of Agronomy annual meeting, Arkansas Crop Management Conference, and at the Molecular and Cellular Biology of the Soybean meeting. Our research on factors limiting soybean yield in highly productive systems was reported at the American Society of Agronomy annual meeting, Georgia-Florida Small Grain Expo, Arkansas Soybean Research Conference, National Agriculture and Food Resource Organization of Japan, Brazilian Soybean Congress, and the Pioneer Hi-Bred Agronomy Leadership Conference. Information on the response of soybean yield and phenology to planting dates and latitude was disseminated at the American Society of Agronomy annual meeting, AgMIP North American Regional Workshop, and the Southern Soybean Breeders' Tour. Our laboratory has also been developing technology that assesses the amount of nitrogen present in corn leaves from the "greenness" values of digital images. This research was disseminated by presentations at the Arkansas Crop Protection Association annual meeting, the American Society of Agronomy annual meeting, and the National Cotton Council Beltwide Cotton Conference. PARTICIPANTS: Individuals working on project: Andy King - program project manager, Marilynn Davies - research technician, Sadal Hwang- postdoctoral associate, Montserrat Salmeron - postdoctoral associate, Alejandro Bolton - graduate research assistant, Hua Bai - graduate research assistant, Upton Siddons - graduate research assistant, Ryan Van Roekel - graduate research assistant. Partner Organizations: Arkansas Soybean Promotion Board, United Soybean Board, MidSouth Soybean Board, North Carolina State University, USDA-ARS, University of Missouri, University of Nebraska, University of Minnesota, University of Florida, University of Georgia, University of Tennessee, Louisiana State University, Mississippi State University, Texas A&M University. Collaborators and contacts: Pengyin Chen University of Arkansas, Douglas Karcher University of Arkansas, Morteza Mozzafari University of Arkansas, James E. Specht University of Nebraska, Jim Orf University of Minnesota, Zenglu Li University of Georgia, Tom Sinclair North Carolina State University, Tom Rufty North Carolina State University, Jeffery Ray USDA/ARS Stoneville MS, Thomas Carter USDA/ARS N.C. State University, Felix Fritschi University of Missouri, Bill Wiebold University of Missouri, Josh Lofton Louisiana State University, Bobby Golden Mississippi State University, Travis Miller Texas A&M University, David Verbree University of Tennessee, Earl Vories USDA/ARS Portageville MO. Training or professional development: Sadal Hwang- postdoctoral associate, Montserrat Salmeron - postdoctoral associate, Alejandro Bolton - graduate research assistant, Upton Siddons - graduate research assistant, Ryan Van Roekel - graduate research assistant, Hua Bai - graduate research assistant. TARGET AUDIENCES: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Crop performance can be considered a response to solar radiation, water availability, and nutrients. A limitation of any, or a combination, of these resources will decrease crop yield. Our research is focused on how these resources can be managed efficiently and to exploit genetic differences in efficiency of resource utilization that can improve crop yields. Previous research has observed differences in how quickly certainly soybean genotypes wilt during the progression of a drought. We identified seven quantitative trait loci (QTLs) in recombinant inbred population segregating for wilting differences. One of these QTL explained 27% of the variation in canopy wilting and is a candidate for introgressing this trait into other germplasm using marker assisted selection. Because soybean grain is particularly high in protein and because soybean typically relies upon nitrogen fixation to meet its nitrogen needs, the remobilization of nitrogen from vegetative tissues to seed has often been considered a limitation to yield. We quantified the amount of nitrogen remobilized under water replete conditions in soybean near-isolines for maturity and found that late-maturing isolines had about twice as much nitrogen in vegetative tissues at the beginning of seedfill as early-maturing lines, but that the amount of nitrogen remobilized and the yields were similar among maturity groups. These results indicate that under these conditions, nitrogen was not a limitation to yield. Additional studies characterized the ability of soybean to recover nitrogen fixation potential following water-deficit stress at different stages of plant development. When stress was imposed during flowering or early seedfilling, nitrogen fixation capacity completely recovered. However, stress during late seedfilling caused premature senescence, a lack of nitrogen fixation recovery, and decreased seed yield.

Publications

• Mastrodomenico, A.T., and L.C. Purcell. 2012. Soybean nitrogen fixation and nitrogen remobilization during reproductive development. Crop Sci. 52:1281-1289.
• Abdel-Haleem, H., T.E. Carter, Jr., L.C. Purcell, C.A. King, L.L. Ries, P. Chen, W. Schapaugh, Jr., T.R. Sinclair, and H.R. Boerma. 2012. Mapping of quantitative trait loci for canopy wilting trait in soybean (Glycine max [L.] Merr). Theor. Appl. Genet. 125:837-846.
• Mastrodomenico, A.T., and L.C. Purcell. 2013. The response and recovery of nitrogen fixation activity in soybean to water deficit at different reproductive developmental stages. Env. Exp. Bot. 85:16-21.
• Fritschi, F.B., J.D. Ray, L.C. Purcell, C.A. King, J.R. Smith, and D.V. Charlson. 2013. Diversity and implications of soybean stem nitrogen concentration. J. Plant Nutr. (in press).
• Raper, T.B., D.M. Oosterhuis, U. Siddons, L.C. Purcell, and M. Mozaffari. 2012. Utilization of the dark green color index to determine cotton nitrogen status. In: N.A. Slaton (ed.) Wayne E. Sabbe Soil Fertility Studies 2011. University of Arkansas Agricultural Experiment Station Research Series. 599:34-36.
• Raper, T.B., D.M. Oosterhuis, U. Siddons, L.C. Purcell, and M. Mozaffari. 2012. Utilization of the dark green color index to determine cotton nitrogen status. In: D.M. Oosterhuis (ed.) Summaries of Arkansas Cotton Research 2011. University of Arkansas Agricultural Experiment Station Research Series. 602:62-65.
• Van Roekel, R.J. and L.C. Purcell. 2012. Soybean yield response to maximum yield environment. Arkansas Crop Protection Association Research Conference. 16:26-27 Nov. 2012.
• Van Roekel, R.J. and L.C. Purcell. 2012. Physiological characteristics of high yield soybean. ASA-CSSA- SSSA International Annual Meetings. 21-24 October. Cincinnati, OH.
• Van Roekel, R.J. and L.C. Purcell. 2012. Soybean yield response to maximum yield environment. ASA-CSSA- SSSA International Annual Meetings. 21-24 October. Cincinnati, OH.
• Salmeron, M. and L.C. Purcell. 2012. Comparison of different modeling approaches to predict soybean phenology in the Mid-South. ASA-CSSA- SSSA International Annual Meetings. 21-24 October. Cincinnati, OH.
• Hwang, S., C.A. King, M.K. Davies, J.D. Ray, P.B. Cregan, and L.C. Purcell. 2012. QTL mapping and primary screening of candidate genes for shoot ureide and nitrogen concentration in soybean (Glycine max). ASA/CSSA Annual Meeting. 22-24 October. Cincinnati, Ohio.
• Prabhu Dhanapal, A., S.K. Singh, J.D. Ray, J. Smith, A. King, L.C. Purcell, and F. Fritschi. 2012. Carbon isotope discrimination and SNP markers association in soybean genotypes. ASA/CSSA Annual Meeting. 22-24 October. Cincinnati, Ohio.
• Singh, S.K., J. Smith, J.D. Ray, L.C. Purcell, and F. Fritschi. 2012. Genotype by environment interaction and stability analysis for carbon isotope discrimination, ureide concentration and nitrogen fixation in soybean. ASA/CSSA Annual Meeting. 22-24 October. Cincinnati, Ohio.
• Raper, T.B., D.M. Oosterhuis, U. Siddons, L.C. Purcell, and M. Mozaffari. 2012. Determination of cotton nitrogen status utilizing a digital camera and imaging software. ASA/CSSA Annual Meeting. 22-24 October. Cincinnati, Ohio.
• Raper, T.B., D.M. Oosterhuis, U. Siddons, L.C. Purcell, and M. Mozaffari. 2012. Determination of cotton nitrogen status from digital image analysis. Proceedings of the 2012 National Cotton Council Beltwide Cotton Conference, January 3-6, Orlando, Florida.

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: Crop production is often limited by the timing and amount of rainfall and the ability to irrigate properly. Genetic differences among soybean cultivars offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Our research evaluating genetic differences in the response of nitrogen fixation in soybean to drought was disseminated through presentations at the American Society of Agronomy annual meeting and at the Soybean Breeders' Workshop. Our research on factors limiting soybean yield in highly productive systems was reported at reported at conferences for the Arkansas Crop Protection Association, Mississippi Crop Consultants, and the Soybean Breeders' Workshop - Technicians' Meeting. Our laboratory has also been developing technology that assesses the amount of nitrogen present in corn leaves from the "greenness" values of digital images. This research was disseminated by presentations at the Arkansas Crop Protection Association annual meeting, and at the American Society of Agronomy annual meeting. PARTICIPANTS: Individuals working on project: Andy King - program project manager; Marilynn Davies - research technician; Sadal Huang- postdoctoral associate; Allejandro Bolton - graduate research assistant; Upton Siddons - graduate research assistant; Ryan Van Roekel - graduate research assistant. Partner Organizations: Arkansas Soybean Promotion Board, United Soybean Board, North Carolina State University, USDA-ARS, University of Missouri, University of Nebraska, University of Minnesota, University of Florida, University of Georgia. Collaborators and contacts: Pengyin Chen, University of Arkansas; Douglas Karcher, University of Arkansas; Morteza Mozzafari, University of Arkansas; Roger Boerma, University of Georgia; Tom Sinclair, North Carolina State University; Jeffery Ray, USDA/ARS Stoneville, MS; Thomas Carter, USDA/ARS N.C. State University; Felix Fritschi; University of Missouri. Training or professional development: Sadal Huang- postdoctoral associate; Allejandro Bolton - graduate research assistant; Upton Siddons - graduate research assistant; Ryan Van Roekel - graduate research assistant. TARGET AUDIENCES: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. PROJECT MODIFICATIONS: Nothing significant to report during the reporting period.

Impacts
Crop performance can be considered a response to solar radiation, water availability, and nutrients. A limitation of any, or a combination, of these resources will decrease crop yield. Our research is focused on how these resources can be managed efficiently and to exploit genetic differences in efficiency of resource utilization that can improve crop yields. Previous research has observed differences in how quickly certainly soybean genotypes wilt during the progression of a drought. We evaluated different physiological traits that might confer differences in wilting among genotypes differing in their wilting response. Results indicated that slow-wilting genotypes generally conserve moisture when water is plentiful by having a lower radiation use efficiency (RUE) than fast-wilting genotypes. One slow-wilting genotype, PI471938, did not appear to conserve soil moisture, but instead appeared to have superior water use efficiency based upon isotope discrimination data. In corn, nitrogen fertilization is important for yield, but applying too much N is expensive and has environmental consequences. Current methods of determining how much N to apply during the season require specialized equipment or have long turn-around times that limit their utility. We developed a method of determining N status of corn leaves by measuring "greenness" of leaves from digital images. Data from two years at multiple locations show that "greenness" is closely associated with leaf N concentration and that "greenness" from digital images taken at tasseling is closely associated with corn grain yield. The only equipment necessary for measuring "greenness" of corn leaves is a digital camera. Similar relationship between leaf nitrogen and greenness was found in cotton.

Publications

• King, C.A., and L.C. Purcell. 2011. Differences in biomass and nitrogen accumulation among soybean genotypes in response to soil water availability. ASA/CSSA Annual Meeting, 19 October 2011, San Antonio, TX.
• Purcell, L.C., and J.T. Edwards. 2011. Are we wasting solar radiation in row crop production ASA/CSSA Annual Meeting, 17 October 2011, San Antonio, TX.
• Singh, S., L.C. Purcell, J.D. Ray, J.R. Smith, and F. Fritschi. Quantification of leaf pigments in soybean based on wavelet decomposition of hyperspectral features. ASA/CSSA Annual Meeting, 17 October 2011, San Antonio, TX.
• Siddons, U., L.C. Purcell, and M. Mozaffari. Dark green color index as a method of real-time in-season corn nitrogen measurement and fertilization. Arkansas Crop Protection Association Annual Meeting. 3 December 2011. Fayetteville, AR.
• Van Roekel, R., and L.C. Purcell. Management practices for maximizing soybean yield. Arkansas Crop Protection Association Annual Meeting. 3 December 2011. Fayetteville, AR.
• Ries, L.L.., L.C. Purcell, T.E. Carter, Jr., J.T. Edwards, and C.A. King. 2012. Physiological traits contributing to differential canopy wilting in soybean under drought. Crop Sci. 52:272-281.
• Gonias, E.D., D.M. Oosterhuis, A.C. Bibi, and L.C. Purcell. 2012. Estimating light interception by cotton using a digital imaging technique. Amer. J. Exp. Agric. 2:1-8.
• Raper, T.B., D.M. Oosterhuis, U. Siddons, L.C. Purcell, and M. Mozaffari. 2012. Effectiveness of the dark green color index in determining cotton nitrogen status from multiple camera angles. Int. J. Appl. Sci. Tech. 2:71-74.
• Bolton, A., and L.C. Purcell. 2011. Nitrogen fixation under drought of soybean genotypes differing in ureide concentration. ASA/CSSA Annual Meeting, 17 October 2011, San Antonio, TX.
• Siddons, U., L.C. Purcell, and M. Mozaffari. Dark green color index as a method of real-time in-season corn nitrogen measurement and fertilization. ASA/CSSA Annual Meeting, 17 October 2011, San Antonio, TX.

Progress 01/01/10 to 12/31/10

Outputs
OUTPUTS: Crop production is often limited by the timing and amount of rainfall and the ability to irrigate properly. Genetic differences among soybean cultivars offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Our research evaluating genetic differences in the response of nitrogen fixation in soybean to drought was disseminated through a presentation at the American Society of Agronomy annual meeting and at the Molecular and Cellular Biology of Soybean meeting. Our research on factors limiting soybean yield in highly productive systems was reported at reported at the American Society of Agronomy annual meeting and at the Arkansas Soybean Research Conference. Our laboratory has also been developing technology that assesses the amount of nitrogen present in corn leaves from the "greenness" values of digital images. This research was disseminated by a US utility patent application (pending) and a presentation at the Arkansas Crop Protection Association annual meeting. PARTICIPANTS: Individuals working on project: Andy King - program project manager, Marilynn Davies - research technician, Sadal Huang- postdoctoral associate, Allejandro Bolton - graduate research assistant, Adriano Mastrodomenico - graduate research assistant, Robert Rorie - graduate research assistant, Upton Siddons - graduate research assistant. Partner Organizations: Arkansas Soybean Promotion Board, United Soybean Board, North Carolina State University, USDA-ARS, University of Missouri, University of Nebraska, University of Minnesota, University of Florida, University of Georgia. Collaborators and contacts: Pengyin Chen - University of Arkansas, Douglas Karcher - University of Arkansas, Morteza Mozzafari - University of Arkansas, James E. Specht - University of Nebraska, Jim Orf - University of Minnesota, Roger Boerma - University of Georgia, Tom Sinclair - North Carolina State University, Tom Rufty - North Carolina State University, Jeffery Ray -USDA/ARS Stoneville, MS, Thomas Carter - USDA/ARS N.C. State University, Felix Fritschi - University of Missouri. Training or professional development: Sadal Huang- postdoctoral associate; Allejandro Bolton - graduate research assistant; Adriano Mastrodomenico - graduate research assistant Robert Rorie - graduate research assistant; Upton Siddons - graduate research assistant. TARGET AUDIENCES: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Crop performance can be considered a response to solar radiation, water availability, and nutrients. A limitation of any, or a combination, of these resources will decrease crop yield. Our research is focused on how these resources can be managed efficiently and to exploit genetic differences in efficiency of resource utilization that can improve crop yields. Nitrogen fertilization is important for corn yield, but applying too much N is expensive and has environmental consequences. Current methods of determining how much N to apply during the season require specialized equipment or have long turn-around times that limit their utility. We developed a method of determining N status of corn leaves by measuring "greenness" of leaves from digital images. Data from two years at multiple locations show that "greenness" is closely associated with leaf N concentration and that "greenness" from digital images taken at tasseling is closely associated with corn grain yield. The only equipment necessary for measuring "greenness" of corn leaves is a digital camera. Digital images could be sent to a website or researcher for quick and inexpensive evaluation of leaf N status. Continuing research is focused on calibrating "greenness" values from young corn plants to determine appropriate amounts of N fertilizer to apply.

Publications

• Purcell, L.C. Physiological challenges for increasing crop yield: resource availability and utilization. Crop Science Society of America, Long Beach, CA. Oct 31- November 3, 2010.
• King, C.A. and L.C. Purcell. A possible link between well-watered shoot-N concentration and dinitrogen fixation response to water deficit among soybean genotypes. Crop Science Society of America, Long Beach, CA. Oct 31- November 3, 2010.
• Purcell, L.C., T.E. Carter, Jr., and H.R. Boerma. Water conversation and prolonged N2 fixation contributions towards drought tolerance. Molecular and Cellular Biology of the Soybean. Durham, NC. 10 August 2010.
• Purcell, L.C. Increasing soybean grain yields - practices to consider. Arkansas Soybean Research Conference. Brinkley, AR. 7 December 2010.
• Siddons, U., L.C. Purcell, and M. Mozaffari. Calibration of image analysis for in-season corn nitrogen fertilization. Arkansas Crop Protection Association Annual Meeting. Fayetteville, AR. 29-30 November 2010.
• Purcell, L.C., R.L. Rorie, and D.E. Karcher. 2011. System and method of determining nitrogen levels from a digital image. US Utility Patent Application (pending).

Progress 01/01/09 to 12/31/09

Outputs
OUTPUTS: Crop production is often limited by the timing and amount of rainfall and the ability to irrigate properly. Genetic differences among soybean cultivars offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Our research evaluating expression of a key gene related to drought tolerance in soybean was disseminated through a publication in the Journal of Experimental Botany, presentations at the American Society of Plant Biologists Annual meeting and presentations at the American Society of Agronomy Annual meetings, a book chapter, and drought-related DNA sequences in soybean that were published in Genbank. Heritability and identification of QTLs associated with delayed wilting under drought in soybean was disseminated through publications in Theoretical and Applied Genetics and in Crop Science. Additional research findings on soybean and corn have been disseminated through peer-reviewed publications in Crop Science, presentations at the American Society of Agronomy, and the Proceedings of the American Seed Trade Association. PARTICIPANTS: Individuals working on project: Andy King - program project manager, Marilynn Davies - research technician, Dirk Charlson - postdoctoral associate, Adriano Mastrodomenico - graduate research assistant; Partner Organizations: Arkansas Soybean Promotion Board, United Soybean Board, North Carolina State University, USDA-ARS, University of Missouri, University of Nebraska, University of Minnesota, University of Florida, University of Georgia. Collaborators and contacts: Pengyin Chen University of Arkansas, Kristopher Brye University of Arkansas, Mary Savin University of Arkansas, Kenneth Korth University of Arkansas, Douglas Karcher University of Arkansas, Morteza Mozzafari University of Arkansas, Marilynn McClelland University of Arkansas, James E. Specht University of Nebraska, Jim Orf University of Minnesota, Roger Boerma University of Georgia, Tom Sinclair North Carolina State University, Tom Rufty North Carolina State University, Jeffery Ray USDA/ARS Stoneville, MS, Thomas Carter USDA/ARS N.C. State University, Felix Fritschi University of Missouri, Clay Sneller Ohio State University. Training or professional development: Dirk Charlson - postdoctoral associate, Sandeep Bhatnagar - postdoctoral associate, Aaron Daigh - graduate research assistant, Robert Rorie - graduate research assistant, Adriano Mastrodomenico - graduate research assistant, Andrea Manfredini - visiting scholar. TARGET AUDIENCES: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Crop performance can be considered a response to solar radiation, water availability, and nutrients. A limitation of any, or a combination, of these resources will decrease crop yield. Our research is focused on how these resources can be managed efficiently and to exploit genetic differences in efficiency of resource utilization that can improve crop yields. Wilting is an easily recognized symptom of drought stress, and we have noted that the severity of wilting differs among soybean genotypes. Using a simple visual-rating system we demonstrated that genotypic ranking of wilting severity is similar over years. We also showed that wilting is a heritable trait and identified chromosomal regions associated with delayed wilting. Our research has also focused on the importance of nitrogen nutrition and genotypic differences in how nitrogen fixation in soybean is affected by drought. We hypothesized that expression of a gene (allantoate amidohydrolase) associated with the catabolism of a product of nitrogen fixation in soybean would decrease in response to drought and be different between drought-tolerant and drought-sensitive genotypes. We rejected this hypothesis and propose that there may be postranslational differences among genotypes that are important in conferring drought tolerance for nitrogen fixation. Our research has also developed a method of determining nitrogen nutritional status of maize by quantifying the greeness of digital pictures take of maize leaves.

Publications

• Charlson, D.V., K.L. Korth, and L.C. Purcell. Allantoate amidohydrolase transcript expression is independent of drought tolerance in soybean. American Society of Plant Biologists Annual Meeting. July 18-22, 2009, Honolulu, HI.
• Charlson, D.V., K.L. Korth, and L.C. Purcell. 2009. Glycine max cultivar Jackson drought responsive element-binding protein (DREB2) genomic, complete cds. GenBank FJ965341.
• Charlson, D.V., K.L. Korth, and L.C. Purcell. 2009. Glycine max cultivar Williams allantoate amidohydrolase mRNA, complete cds. GenBank FJ796239.
• Charlson, D.V., and L.C. Purcell. 2009. Glycine max cultivar Jackson drought responsive element-binding protein (DREB1) genomic, complete cds. GenBank FJ965342.
• Charlson, D.V., K.L. Korth, and L.C. Purcell. 2009. Allantoate amidohydrolase transcript expression is independent of drought tolerance in soybean. J. Exp. Bot. 60:847-851.
• Charlson, D.V., S. Bhatnagar, C.A. King, J.D. Ray, C.H. Sneller, T.E. Carter, Jr., and L.C. Purcell. 2009. Polygenic inheritance of canopy wilting in soybean [Glycine max (L.) Merr.]. Theor. Appl. Genet.119:587-594.
• King, C.A., and L.C Purcell. 2009. Dynamics of shoot nitrogen and ureide concentrations during crop development among diverse soybean genotypes. American Society of Agronomy and Crop Science Society of America National Meeting. November 1-5,. Pittsburgh, PA.
• King, C.A., L.C. Purcell, and K.R. Brye. 2009. Differential wilting among soybean genotypes differing in response to water deficit. Crop Sci. 49: 290-298.
• Mastrodomenico, A.T., L.C. Purcell, and C.A. King. 2009. Soybean nitrogen fixation at different reproductive stages and water regimes. American Society of Agronomy and Crop Science Society of America National Meeting. November 1-5, Pittsburgh, PA.
• Purcell, L.C. T.E. Carter, Jr., T.R. Sinclair, C.A. King, P.Chen, H.R. Boerma, J.D. Ray, D.V. Charlson, J.H. Orf, J.E. Specht, T.W. Rufty, and F. Fritschi. 2009. Tweaking the genetics and physiology of soybean to increase dryland yields. Proceedings of the 39th Soybean Seed Research Conference, CD-ROM, American Seed Trade Association, Alexandria, VA.
• Purcell, L.C. 2009. Physiological responses of N2 fixation to drought and selecting genotypes for improved N2 fixation. p. 211-238. In: (eds. H.B. Krishnan and D.W. Emerich) Nitrogen Fixation in Crop Production. Agron. Monogr. 52. ASA CSSA SSSA, Madison, WI.
• Purcell, L.C., K.R. Brye, M.R. McClelland, and M.C. Savin. 2009. Comment on "Preplant herbicides don't increase forage production of cereal rye interseeded into bermudagrass" by Brandon Bruce, Robert L. Kallenbach, Kevin Bradley, and Ben Fuqua, Agron. J. 101:1175-1181 (2009). Agron. J. 102:58-59.
• Rorie, R.L., L.C. Purcell, D.E. Karcher, C.A. King, and M Mozzafari. 2009. Characterizing leaf N with digital images and the association of greenness with yield. American Society of Agronomy and Crop Science Society of America National Meeting. November 1-5, Pittsburgh, PA.
• Savin, M.C., L.C. Purcell, A. Daigh, and A. Manfredini. 2009. Response of mycorrhizal infection to glyphosate applications and P fertilization in glyphosate tolerant soybean, maize, and cotton. J. Plant Nutr.32:1702-1717.

Progress 01/01/08 to 12/31/08

Outputs
OUTPUTS: Drought stress in the Midsouthern U.S.A. is the primary limitation to consistent high crop yields. Coupled with low yields in rainfed environments is a limitation in the quantity and quality of water that is available for irrigation. Management strategies and genetic differences among cultivars (or hybrids) of our major crops offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Our research evaluating maize radiation interception has been disseminated through a publication in Maydica. Research findings on soybean have been disseminated through peer-reviewed publications in Crop Science Theoretical and Applied Genetics, presentations at the American Society of Agronomy, and a presentation at the Integrated Crop Management Conference. PARTICIPANTS: Individuals working on project: Andy King - program project manager; Marilynn Davies - research technician; Dirk Charlson - postdoctoral associate; Landon Ries - graduate research assistant; Xiaoyan Hu - graduate research assistant; Robert Rorie - graduate research assistant; Adriano Mastrodomenico - graduate research assistant; Thomas M. Seversike - graduate research assistant; Partner Organizations: Arkansas Soybean Promotion Board, United Soybean Board, North Carolina State University, USDA-ARS, University of Missouri, University of Nebraska, University of Minnesota, University of Florida, University of Georgia. Collaborators and contacts: Pengyin Chen University of Arkansas; Kristopher Brye University of Arkansas; Mary Savin University of Arkansas; Jeremy Ross University of Arkansas; Michael Popp University of Arkansas; Dick Oliver University of Arkansas; Ed Gbur University of Arkansas; Douglas Karcher University of Arkansas; James E. Specht University of Nebraska; Jim Orf University of Minnesota; Roger Boerma University of Georgia; Tom Sinclair University of Florida; Jeffery Ray USDA/ARS Stoneville, MS; Thomas Carter USDA/ARS N.C. State University; Felix Fritschi University of Missouri; Training or professional development: Dirk Charlson - postdoctoral associate; Landon Ries - graduate research assistant; Xiaoyan Hu - graduate research assistant; Robert Rorie - graduate research assistant; Adriano Mastrodomenico - graduate research assistant; Tomas Saralangue - visiting scholar; TARGET AUDIENCES: Target audiences include the scientific community, agricultural extension personnel, agricultural consultants, and agricultural producers. Efforts to reach these audiences include publication of scientific research, oral and written presentations and scientific meetings, presentations at meetings for agricultural consultants and farmers, and cooperating with popular press on agricultural articles for the lay audience. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
A critical resource that is often not considered in evaluating crop performance is the amount of solar radiation intercepted by the crop. One reason this is often neglected is that current techniques for measuring intercepted radiation are time consuming and can only be used for approximately two hours per day. We have developed tools using a standard digital camera and off-the-shelf software that has simplified this measurement considerably and have been demonstrated successfully in maize, cotton, and soybean. One method that could be used to increase solar radiation interception is increasing population density and narrowing row spacing, and these management strategies have been effective in increasing yield in short-season soybean and maize production systems. However, increased seeding rates substantially increases production costs. We considered a genetic trait that confers 7 leaflets in soybean rather than the usual 3 leaflets as a means to increase solar radiation interception. We successfully mated 3 and 7 leaflet soybean and used molecular markers to map this trait. In understanding the importance of water availability for crop performance, we have measured soybean genotypes for their ability to accumulate plant mass for each unit of solar radiation intercepted, which is defined as radiation use efficiency (RUE). Our data indicate that under fully-irrigated conditions, those genotypes that wilt slowly during drought, tend to have lower RUE values than genotypes that wilt quickly. The slow wilting genotypes conserve soil moisture when moisture is plentiful and are able to utilize that moisture later in the season compared with fast-wilting genotypes that rapidly exhaust soil-moisture.

Publications

• Charlson, D.V., and L.C. Purcell. Convergent evolution of ureide-catabolizing enzymes in plants and animals. American Society of Agronomy and Crop Science society of America National Meeting. Houston, TX. October 6-9, 2008.
• Gonias, E.D., D.M. Oosterhuis, A.C. Bibi, and L.C. Purcell. Estimating light interception by the cotton crop using a digital imaging technique. Beltwide Cotton Conferences. Nashville, TN. January 8-11, 2008.
• Hu, X., and L.C. Purcell. Comparative responses of early-maturing and late-maturing soybean culitvars to an irrigation gradient. American Society of Agronomy and Crop Science society of America National Meeting. Houston, TX. October 6-9, 2008.
• Purcell, L.C. Resources needed for record-breaking soybean yields. Integrated Crop Management Conference. Ames, IA. December 11, 2008.
• Purcell, L.C., and and W.J. Ross. Extreme agriculture: What do maximum yields mean American Society of Agronomy and Crop Science society of America National Meeting. Houston, TX. October 6-9, 2008.
• Ries, L., and L.C. Purcell. Radiation and water use efficiency of soybean genotypes that differ in wilting response under drought. American Society of Agronomy and Crop Science society of America National Meeting. Houston, TX. October 6-9, 2008.
• Saralangue, T., L.C. Purcell, and D.E. Karcher. 2008. Estimating the fraction of radiation intercepted in maize by digital-image analysis. Maydica 53:63-68.
• Seversike, T.M., J.D. Ray, J.L. Shultz, and L.C. Purcell. 2008. Soybean lf2 gene maps to the linkage group B1 of the molecular map. Theor. Appl. Genet.117:143-147.

Progress 01/01/07 to 12/31/07

Outputs
Drought stress in the Midsouthern U.S.A. is the primary limitation to consistent high crop yields. Coupled with low yields in rainfed environments is a limitation in the quantity and quality of water that is available for irrigation. Management strategies and genetic differences among cultivars (or hybrids) of our major crops offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. In maize, our previous research determined that very short-season hybrids (~85 day) had yields similar to full-season hybrids (~120 days) when grown in narrow rows (50 cm) at increased population densities (~10 plants m-2). We evaluated the developmental plasticity of several maize hybrids differing in maturity when sown at a range of population densities. These results have been published in a peer-reviewed manuscript. Crop simulation analysis was undertaken to evaluate the importance of crop residue for decreasing soil surface evaporation in soybean no-tillage production systems. Results from this research have been disseminated through a peer-reviewed publication. A simulation analysis was also undertaken to evaluate yield and biomass response to the cumulative amount of transpiration from a wide range of soybean maturity groups (MG, 0 through VI) when grown under well watered conditions with population densities ranging from 10 to 100 plants m-2. Results from this simulation analysis have been published in a peer-reviewed publication and have been presented at the American Society of Agronomy annual meetings. Over several years our research has found that there are genetic differences in the tolerance of N2 fixation to drought in soybean. A breeding program was initiated in 1993 that crossed an older, low yielding genotype with drought tolerant N2 fixation with a newer, high yielding genotype that was drought sensitive for N2 fixation. The results from this breeding program, along with physiological measurements, are reported in two peer-reviewed manuscripts.

Impacts
Cooperative research evaluating maize plasticity to population density has shown that, in general, short-season hybrids are much less plastic than are full-season hybrids. This research helps explain why different maize hybrids respond differently to population density. Simulation analysis of soybean yields in response to soil water and how no-till production systems affect soil-water balance provide clear evidence of the advantage that no-till has on conserving soil moisture. Soil moisture that is saved by no-till practices is available for the crop and often result in yield increases. These simulations also determined that estimates of the beginning soil-water balance at the beginning of the season were needed to predict soybean yield responses. Simulations of the response of yield of well-watered soybean to the estimated amount of cumulative transpiration from emergence to R6 gave surprising results. Long established crop theory would predict that yield would increase linearly as the cumulative amount of water transpired increased. Our data indicate that yield response to increased amounts of cumulative transpiration are curvilinear and reach an asymptote, similar to yield responses to increased nutrients. These results show that full-season soybean cultivars (MG VI) under well-watered conditions transpire about 200 mm more water than MG II cultivars but have similar yields. A soybean breeding project to transfer drought-tolerant N2 fixation to high-yielding lines was successful. Two breeding lines developed showed superior yields to check cultivars when drought conditions were moderate. These drought tolerant soybean lines have been released and made publically available.

Publications

• Chen, P., C.H. Sneller, L.C. Purcell, T.R. Sinclair, C.A. King, and T. Ishibashi. 2007. Registration of soybean germplasm lines R01-416F and R01-581F for improved yield and nitrogen fixation under drought stress. J. Plant Reg. 1:166-167.
• Purcell, L.C., J.T. Edwards, and K.R. Brye. 2007. Soybean yield and biomass responses to cumulative transpiration: Questioning widely-held beliefs. Field Crops Res. 101:10-18.
• Saralangue, T., F. Andrade, P.A. Calvino, and L.C. Purcell. 2007. Why do maize hybrids respond differently to variations in plant density? Agron. J.99:984-991.
• Sinclair, T.R., L.C. Purcell, C.A. King, C.H. Sneller, P. Chen, and V. Vadez. 2007. Drought tolerance and yield increase of soybean resulting from improved symbiotic N2 fixation. Field Crops Res. 101:68-71.
• Sinclair, T.R., L.R. Salado-Navarro, G. Salas Graciela, L.C. Purcell. 2007. Soybean yields and soil water status in Argentina: Simulation analysis. Agric. Sys. 94:471-477.
• Charlson, D., S. Bhatnagar, C.A. King, L.C. Purcell, J.D. Ray, C.H. Sneller, and T.E. Carter. Identification of quantitative trait loci for delayed wilting in soybean. American Society of Agronomy annual meetings. New Orleans, LA. 4-8 November 2007.
• Hu, X., and L.C. Purcell. Comparative responses of early-maturing and late-maturing soybean cultivars to an irrigation gradient. Arkansas Crop Protection Association annual meeting, Fayetteville, AR. 26-27 November 2007.
• King, C.A., and L.C. Purcell. Genotypic differences for shoot N and ureide concentrations in soybean. American Society of Agronomy annual meetings. New Orleans, LA. 4-8 November 2007.
• Purcell, L.C., and D. Stephenson. Short-season maize production in the Midsouthern U.S. American Society of Agronomy annual meetings. New Orleans, LA. 4-8 November 2007.
• Ries, L.L., and L.C. Purcell. Radiation use efficiency of soybean genotypes that differ in wilting under drought. Arkansas Crop Protection Association annual meeting, Fayetteville, AR. 26-27 November 2007.
• Rzewnicki, P., T.E. Carter, L.C. Purcell, P. Chen, H.R. Boerma, and T.R. Sinclair. Yield of slow-wilting soybean breeding lines in high- and low-yielding environments in the Southern USA. American Society of Agronomy annual meetings. New Orleans, LA. 4-8 November 2007.

Progress 01/01/06 to 12/31/06

Outputs
Drought stress in the Midsouthern U.S.A. is the primary limitation to consistent high crop yields. Coupled with low yields in rainfed environments is a limitation in the quantity and quality of water that is available for irrigation. Management strategies and genetic differences among cultivars (or hybrids) of our major crops offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Crops of maize and soybean that are typically grown in the Midsouth mature in 110 to 130 days and may require as many as 8 to 10 irrigations. Short season crops of maize and soybean that mature in 70 to 100 days have yields similar to full-season crops when irrigated properly and when grown in narrow rows at high population densities, but production of short-season maize and soybean require 30 to 50% less irrigation than their full-season counterparts. Economic tradeoffs for maize and soybean were considered for yield, seeding rate, irrigation amounts, and seasonal market fluctuations. In maize, short-season and full-season hybrids were similar in terms of yield and partial returns, but profit-maximizing seeding rates were higher for short-season hybrids than full-season hybrids. Other economic factors, however, did not offset increased seeding costs for short-season hybrids. In soybean, optimal seeding rates were substantially lower for late-maturing soybean (MG IV through VI) than early-maturing cultivars (MG I through III), and yield of late-maturing cultivars was less affected by partial stand loss. A broad range of soybean maturities (MG II through VI) offers advantages in risk management. Physiological studies targeting increased drought tolerance of nitrogen fixation in soybean, has found that genotypes that have high shoot nitrogen concentration under well-watered conditions appear to have greater decreases in nitrogen fixation during drought than those genotypes with low shoot nitrogen concentration. Additionally, those genotypes having high shoot nitrogen concentration also had high shoot ureide concentrations. In previous studies high shoot ureide concentration was associated with sensitivity of nitrogen fixation to drought.

Impacts
Short-season crops of maize and soybean offer a means to maintain high yields but substantially decrease irrigation requirements. Profit-maximizing seeding rates are higher in short-season maize and soybean than full-season crops. Physiological studies in soybean indicate that shoot nitrogen concentration in well-watered plants is an important determinant of the ability to continue nitrogen fixation during drought.

Publications

• Purcell, L.C.. 2006. Redefining the requirements for light and water in soybean for irrigated and high yielding environments. p.83-89. Proceedings of the14th Congress of AAPRESID, Argentinean No-Till Farmer's Association. 8-11 August 2006, Rosario, Argentina.
• Popp, M., J.T. Edwards, and L.C. Purcell. 2006. Plant population density and maturity effects on profitability of short-season maize production in the Midsouthern USA. Agron. J. 98:760-765.
• Popp, M.P., J.T. Edwards, L.C. Purcell, and P.M. Manning. 2006. Profit-maximizing seeding rates and replanting thresholds for soybean: Maturity group interactions in the Mid-South. Agric. Syst. 91:211-228.
• King, C.A., and L.C. Purcell. 2006. Genotypic variation for shoot-N concentration and response to water deficits in soybean. Crop Sci. 46:2396-2402.

Progress 01/01/05 to 12/31/05

Outputs
Drought stress in the Midsouthern U.S.A. is the primary limitation to consistent high crop yields. Coupled with low yields in rainfed environments is a limitation in the quantity and quality of water that is available for irrigation. Management strategies and genetic differences among cultivars (or hybrids) of our major crops offer the potential to alleviate yield decreases associated with drought and to decrease the quantity of water required for crop irrigation. Crops of maize and soybean that are typically grown in the Midsouth mature in 110 to 130 days and may require as many as 8 to 10 irrigations. Short season crops of maize and soybean that mature in 70 to 100 days have yields similar to full-season crops when irrigated properly and when grown in narrow rows at high population densities, but production of short-season maize and soybean require 30 to 50% less irrigation than their full-season counterparts. By monitoring crop light interception in maize and soybean over a wide range of population densities and maturites, the cumulative amount of photosynthetically active radiation (CIPAR) intercepted during the season has been estimated. Surprisingly, the response of yield to CIPAR was curvilinear and reached 90% of the asymptotic yield at approximately 800 MJ m-2 (maize) and 600 MJ m-2 (soybean) of CIPAR. For full-season crops, relatively few plants m-2 are required to cumulate this amount of CIPAR, but for short-season crops, increased populations are necessary. This information has been used to determine minimum population densities required to achieve 90% of the asymptotic yield and may serve as a means to estimate replanting thresholds. Physiological studies have also been targeted at increasing the drought tolerance of N2 fixation in soybean, which is a key process for yield but is especially sensitive to drought. Differences in sensitivity and tolerance to drought have been noted in previous experiments to be partially due to the ability to degrade the final products of N2 fixation (ureides) in leaves. The catabolism of ureides is dependent upon manganese, which serves as a cofactor for an enzyme in ureide breakdown. Controlled environment experiments found that recovery of N2 fixation from exogenous applications of ureides was hastened by manganese fertilization. Although drought increased ureide accumulation in soybean shoots and decreased N2 fixation, recovery from water deficit did not appear to be associated with ureide catabolism. Instead, it appears that intermediary products of ureide catabolism may be important in signaling nodules to decrease N2 fixation.

Impacts
Short-season crops of maize and soybean offer a means to maintain high yields but substantially decrease irrigation requirements. Furthermore, the yield response of maize and soybean to the cumulative amount of light intercepted during the season can be used to determine optimum population densities for a wide range of crop maturities, and it may be used to estimate economical replanting thresholds. Physiological studies in soybean evaluating drought tolerance of N2 fixation offer a novel means of ameliorating drought impacts using a trait that confers physiological and biochemical advantages.

Publications

• King, C.A., and L.C. Purcell. 2005. Inhibition of N2 fixation in soybean is associated with elevated ureides and amino acids. Plant Physiol. 137:1389-1396.
• Edwards, J.T., and L.C. Purcell. 2005. Soybean [Glycine max (L.) Merr.] plant population responses among diverse maturity groups: I. Agronomic characteristics. Crop Sci. 45:1770-1777.
• Edwards, J.T., L.C. Purcell, and D.E. Karcher. 2005. Soybean [Glycine max (L.) Merr.] plant population responses among diverse maturity groups: II. Light interception and utilization. Crop Sci. 45:1778-1785.
• Edwards, J.T., L.C. Purcell, and E.D. Vories. 2005. Light interception and yield potential of short-season maize (Zea mays L.) hybrids in the Midsouth. Agron. J. 97:225-234.
• Edwards, J.T., and L.C. Purcell. 2005. Light interception and yield response of ultra-short-season soybean (Glycine max) to dipheneylether herbicides in the midsouthern U.S.A. Weed Tech. 19:168-175.
• Sinclair, T.R., and L.C. Purcell. 2005. Is a physiological perspective relevant in a genocentric age? J. Exp Bot.56:2777-2782.
• King, C.A., and L.C. Purcell. 2005. Herbicide resistant dinitrogen fixing bacteria and method of use. U.S. Patent #6,872,562 B2. Issued 29 March 2005.