Progress 10/01/06 to 09/30/11
Outputs
OUTPUTS: Our contribution to this multistate project falls mainly under Objective #1: To develop a greater fundamental knowledge of the processes controlling soil N and C cycling, with particular attention to the role of factors such as soil, climate and cropping systems on the amounts of soil N supplied to crops and N loss from soils. More specifically, to understand the impact of soil management on microbial processes underlying soil N and C cycling in relation to C sequestration, plant nutrient supply, and greenhouse gas production. Previous studies have shown that management of nitrogen and crop residues to promote residue decomposition can lead to soil C and nitrogen (N) sequestration. In this study we assess the role of soil aggregates after conversion from no-till (NT) to conservation-plow tillage in the fall with N fertilization (RT+N) under continuous maize rotation in an irrigated field plot. Soil cores were collected in the fall of 2005, 2006, 2007 and 2008 from a continuous maize rotation field, separated into 0-5, 5-15 and 15-30 cm depths, air dried and wet sieved to obtain >250μm, 250-53 μm and <53 μm aggregate size classes. Breakdown of >250μm aggregates and mixing of the 0-5 and 5-15 cm soil layers resulted from the conservation-plow tillage following NT. No changes in the proportion of aggregate sizes were observed in the 15-30 cm soil layer. Cumulative C mass for the first 150 and 300 kg soil/m2 was 3.49 and 5.68 kg C/m2 in 2005 and 3.52 and 5.24 kg C/m2 in 2008, respectively. The reduction in C storage in the largest aggregates is associated with the breakdown of aggregates and loss of the LF pool. The increase in C storage in the middle and small size aggregates with depth is associated to an increase in humic material in these aggregates. PARTICIPANTS: Principle Investigator: Rhae Drijber. Technologist: Elizabeth Jeske. Collaborators: NC1195 committee members, Daniel Olk, Shashi Verma, John Linquist, Charles Francis, Virginia Jin, Tim Arkebauer, Ken Cassman, Dave Wedin. Graduate Student Training: Anita Wingeyer, Elizabeth Jeske TARGET AUDIENCES: Research findings were presented at the International ASA-CSA-SSSA annual meeting in Long Beach CA. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Long-term irrigated corn-soybean rotations located in eastern Nebraska were unable to sequester additional C under variable C and N inputs, and tillage regime. This was demonstrated using archived samples and conversion of measured C stocks to a mass basis. Nevertheless, incorporation of maize residues by conservation tillage along with nitrogen fertilizer (RT+N) has been shown to speed up residue decomposition under high inputs of maize residues. Introduction of RT+N in the fall did not modify the total amount of stored C in the 0-30 cm soil depth (0-400 kg soil m-2), but changed its distribution. Our results indicate that the incorporation of the residues in the soil along with N fertilizer in the conservation-plow system favored the decomposition of the residues to humic materials, while it exposed the more labile short term storage C pools (free and occluded LF in the larger aggregates) to decomposition.
Publications
- Wortman, S., J. Lindquist, R. Drijber, M. Bernards, C Francis. Mulching cover crop mixtures to increase weed supression, soil moisture and grain yield. ASA-CSSA-SSSA Annual Meetings, Long Beach, CA. Oct. 31 - Nov. 3, 2010.
- Haddix, M.L., Plante, A.F., Conant, R.T., Paul, E.A., Six, J., Steinweg, M.J., Magrini-Bair, K., Drijber, R.A., Morris, S.J. 2011. The role of soil characteristics on temperature sensitivity of soil organic matter. Soil Science Society of America Journal 75:56-68.
|
Progress 10/01/09 to 09/30/10
Outputs
OUTPUTS: During this reporting year a transition occurred with the passing of Dr. Dan Walters. Thus I am reporting on current student activities arising from Dan's on-going research projects. Agustin Martelloto MS thesis research examined changes in SOC in two long-term experiments; one an irrigated site with continuous corn (CC) and corn-soybean(CS) rotation and three N rates; and the other a rainfed site with three tillage treatments, two crop sequences (CC and CS) and three N application rates. Soil samples taken at early stages of the experiments were used as a benchmark to analyze carbon trends over time. In spite of considerable differences in C and N inputs, SOC amount and distribution was largely unchanged. In contrast, tillage had a significant impact on carbon change as more carbon was lost under moldboard plow than under no-till or disk. None of the evaluated treatments under the conditions of these experiments were able to sequester atmospheric C since all lost SOC over time. The use of archived samples made possible the determination of the rate of SOC change over time, and allowed an accounting for natural soil variability. Anita Wingeyer's PhD research builds on prior research indicating that management of nitrogen and crop residues to promote residue decomposition can lead to soil C and nitrogen (N) sequestration. Conservation tillage plus N fertilizer (RT+N) has been used to speed up residue decomposition under high inputs of maize residues. Fall RT+N did not modify the total amount of stored C in the 0-30 cm soil depth (0-400 kg soil m-2), but changed its distribution. Changes in whole soil C mass per depth reflects changes in the C stored by >250 aggregates, and was associated with a proportional change in this aggregate fraction. RT+N also favored humification of the corn residue into both MHA and CaHA fractions. Liz Jeske's PhD research examines the impact of N rate on fungal biomass in maize systems. To assess the impact of N rate on the soil fungal community five rates of N (0, 50, 100, 150 and 300 kg ha-1 urea) were applied to corn and soybeans grown under minimum-till management. Over the growing season, saprophytic fungi in soil responded differently to the presence of corn versus soybeans. In spite of the larger amount of residue provided by the corn crop, the fungal biomarker C18:2c9,12 was not significantly higher under CC compared to CB, suggesting that residue chemistry plays an important role. The promotion of saprophytic fungal growth following soybeans may also explain why some of the N credit comes at the expense of native soil N. This is also supported by the similar extradical AMF biomass under 0 kg N ha-1 CB and higher fertility CC. The colonization of maize roots by AMF was not influenced by N rate or crop rotation but the diversity of the AMF community declined at the highest N rate. Crop rotation and N rate had no significant influence on total C or total N in this system even after 13 years. The large AMF hyphal production in soil under corn receiving little or no N may be a prominent C sink. PARTICIPANTS: The research report for this year encompasses three graduate students. TARGET AUDIENCES: Rsearch findings were presented at the International Soil Science Society of America annual meeting in Long Beach CA. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Long-term irrigated corn-soybean rotations located in eastern Nebraska were unable to sequester additional C under variable C and N inputs, and tillage regime. This was demonstrated using archived samples and conversion of measured C stocks to a mass basis. Nevertheless, incorporation of maize residues by conservation tillage along with nitrogen fertilizer (RT+N) has been shown to speed up residue decomposition under high inputs of maize residues. Introduction of RT+N in the fall did not modify the total amount of stored C in the 0-30 cm soil depth (0-400 kg soil m-2), but changed its distribution. Our results indicate that the change in placement of the crop residues plus N addition resulted in a more uniform distribution of C (mixing) in the 0-30 cm layer, favored humification of crop residues, and led to an increase in the storage of humified C in both aggregate sizes, despite a reduction in >250 aggregate fraction.
Publications
- Agustin Martelloto. 2010. The impact of long-term tillage, crop rotation and N application on soil carbon sequestration. MS Thesis, University of Nebraska.
- Martellotto, A., D.T. Walters, C.A. Shapiro. 2010. Carbon Sequestration: The Lack of Initial Measurement Could Bias Interpretations of Management Effect on Soil Carbon. ASA-CSSA-SSSA Annual Meetings, Oct. 31 - Nov. 3, 2010. Long Beach CA.
- Jeske, E.S., R. Drijber, H. Tian, D. Walters. 2010. Soil microbial community response to nitrogen rate in a long-term, no-till continuous corn and corn/soybean rotation. ASA-CSSA-SSSA Annual Meetings, Oct. 31 - Nov. 3, 2010. Long Beach CA.
- Wingeyer, A., D. Walters, T. Arkebauer, K. Cassman, R. Drijber, C. Francis, D. Olk, S. Verma, D. Wedin. Soil C sequestration from no-till to conservation plow-tillage: role of protected soil niches. ASA-CSSA-SSSA Annual Meetings, Oct. 31 - Nov. 3, 2010. Long Beach CA
- Wingeyer, A., D. Walters, S. Verma, T. Arkebauer, K. Cassman, C. Francis, D. Wedin, D. Olk, R. Drijber. Effective soil C sequestration: role of protected niches. ASA-CSSA-SSSA Annual Meetings, Oct. 31 - Nov. 3, 2010. Long Beach CA.
|
Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: During this reporting year, several significant outputs were produced. The first are the publications outlining the influence of soil management and cropping system on the rate of decomposition of crop residues (stalk and root). Completed during this year was an analysis of the residual effect of changes in soil quality as a result of crop (Maize and soybean) intensification on N sequestration and storage of and release of indigenous soil N via mineralization during the growing season. During 2008 we noted a significant increase in soil C sequestration and concomitant increase in indigenous N supply as a function of long-tern (8 years) of high plant population and elevated N additions under continuous corn. Average crop yields in this experiment were close to the yield potential of soybean and corn at this location and significantly higher than the national or state average. Corn yields were generally in the 215 to 287 bu/a range or within 84 to 97% of the simulated yield potential. Corn following soybean yielded about 5 to 11% higher than continuous corn primarily due to fewer problems with stand establishment and fewer pest and disease problems. Despite the large biomass production in our high yielding corn systems, peak growing season (about 36 to 55 lb/acre/day) soil CO2 efflux was within typical ranges for arable crops. In a complete 2-year crop rotation with flux measurements conducted in corn and soybean, soil CO2 efflux (respiration) in the continuous corn systems was 22% larger than in corn-soybean rotations at both levels of management intensity. Within each crop rotation, intensified fertility management did not cause a significant increase in soil CO2 emissions as compared to the recommended practice. As a result, both SOC and total soil N (TSN) increased in the two continuous corn (CC) systems (both intensive and recommended management), but decreased in the corn-soybean rotation under recommended management (CS-rec) or remained unchanged in the CS-int system. On average, SOC declined at an average rate of 275 lb/acre/yr in the CS-rec, whereas it increased at a rate of 565 lb N/acre/yr in the CC-intensive (0-12 inch depth). Similar trends were observed for TSN. In the intensive continuous corn systems,incorporation of large amounts of residue C and N has led to a significant build-up of SOM over just a few years. Additional work on the influence of soil, fertilizer, and water management on residue decomposition rate were completed. We used three production-scale agricultural fields at the University of Nebraska Agricultural Research and Development Center near Mead, NE. Each field was no-till, where the grain was harvested at the end of the growing season, but the remainder of the plant including the seedless cob, stalks, leaves, as well as all of the belowground portions of the plant were left in the field to decompose without being incorporated into the soil matrix via tillage. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: The majority of activities reported are targeted to the scientific community (i.e researchers in academic institutions). In the case of our regional evaluation of the Illinois soil N test, we have specifically targested the Crops and Soils article to Certified Professional Agronomists and Soil Scientists PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
We found that irrigation/fertigation management increased litter inputs, led to changes in plant tissue quality, had no effect on carbon allocation, and increased decomposition rates. This balance of both greater litter inputs and outputs of C from the irrigated management regimes led to a similar litter-C balance for this litter cohort in the irrigated and rainfed management regimes after 3 years of decomposition. Our data clearly show that merely increasing litter-C inputs through irrigation/fertigation practices is not sufficient to increase litter-C residence time because decomposition rates also increase. Therefore, close monitoring of decomposition rates is essential for understanding litter-C pool dynamics. When fossil fuel consumption, CO2-C losses and trace gas emissions are factored into total global warming potential (GWP) of our study of intensified systems systems, all four cropping systems were net sources of GHG, with GWP ranging from 0.54 to 1.02 tons of CO2-C/acre/year. Positive or negative changes in SOC, intrinsic C costs associated with crop production and soil N2O emissions were major contributors to the net GWP. The oxidation of CH4 (methane) by these soils gave only a small mitigation capacity (Table 3). Nitrogen fertilizer (16 to 36%), energy used for irrigation (15 to 22%), electricity for grain drying (13 to 18%), diesel (10 to 16%), and lime (9 to 13%) were the major components of the C costs associated with agricultural production. Despite higher C costs associated with agricultural production and also higher N2O emissions, net GWP in the continuous maize systems was lower than that of the corn-soybean systems because sequestration of atmospheric CO2 in SOC was observed only in the CC systems. Although the amount of N fertilizer N applied to corn grown in the intensive cropping systems was 40% (CC) or 64 to 92% (CS) greater than the recommended treatments, N2O losses were not directly related to the level of N input only. Significant N2O losses were observed during the soybean year especially after soybean harvest.
Publications
- Kochisek, A.E., J. Knops, D.T.Walters, and T.J. Arkebauer. 2009. Impacts of management on decomposition and litter carbon balance in irrigated and rainfed no-till agricultural systems. Agricultural and Forest Metorology 149: 1983-1993.
- Salvagiotti, F., J.E. Specht, K.G. Cassman, D.T. Walters, A. Weiss, and A. Dobermann. 2009. Growth and Nitrogen Fixation in High-Yielding Soybean: Impact of Nitrogen Fertilization. Agron. J. 101:958-970.
- Wortmann, C.S., A.R. Dobermann, R.B. Ferguson, G.W. Hergert, C.A. Shapiro, D.D. Tarkalson, D. Walters. 2009. High-yielding corn response to applied phosphorus, potassium, and sulfur in Nebraska. Agron. J. 101:546-555.
- Shapiro, C.A., R. Fergusen, G. Hergert, C. Wortmann, D. Walters. 2009. Fertilizer Suggestions for Corn. EC117. University of Nebraska Extension Division 6pp.
- Walters, D.T. 2009. Managing to reduce greenhouse gas emissions. Fluid Fertilizer Journal. 16(3) Issue 61.
- Walters, D.T., K. Cassman, J. Specht, A. Liska, H. Yang, T. Setiyono and A. Wingeyer. 2009. Ecological Intensification of Corn-based systems: Soil quality changes impact yield. In. L.S. Muphy (ed) Proceedings of the 2009 Fluid Forum, Feb, 16-18, 2009, Scottsdale, AZ. pp. 62-70.
- Walters, D.T., H. Yang, T.Setiyono, K. Cassman and A.Dobermann. 2009. Maize-N, a quasi-mechanistic model for formulating maize-N fertilizer recommendations. Paper presented at the Soil Science Society of America annual meeting. Nov 4, Pittsburgh PA.
|
Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: During this reporting year, several significant outputs were produced. The first was a refereed journal article on the North Central Regional evaluation of the Illinois soil N test. This test has been controversial because of the varying degree of success reported in different regions of the country. This article was also released in the Crops and Soils Journal whereby CEU credits in soil and water management could be earned by certified professionals. Additional work was completed in the evaluation of meaningful soil organic matter pools. In this experiment, soils labeled with 15N were incubated for 1-year under an intense immobilization regime stimulated by the addition of high C:N ratio plant material. The fate of N in two humic acid pools , the mobil humic acid (MHA) and Ca humate (CaHA) pools was monitored. These pools are unique form each other in that the MHA is rich in N (approximately 5% N ) and has a 14C determined carbon mean residence time (MRT) that is modern. The CaHa pool is more condensed, has a lower N content and a 14C MRT that is in the 800-1200 year range. Both 14C carbon aging and change in mass of these pools was measured before and after the 1-year incubation. The results of this incubation was reported in a paper presented at the SSSA annual meeting in Houston, TX. In addition to this experiment, a refereed article was published reporting on a new technique for the determination of 13C signature on small volumes of soil respiratory gas (<10 ml) taken in the field. We also shared these results in a number of oral presentations at scientific meetings in 2007. Soil organic matter studies from a long-term maize intensification experiment was completed in 2008. Here we measured the change in soil carbon and in the change in the size of the indigenous soil N pool as a function of both residue carbon input and fertilizer N input. The results have been reported in several scientific meetings in 2008. The culmination of uptake data gathered in the NC 1032 core experiment has become the basis of the empirical database driving a dynamic physiological and resource use efficiency generation within a mechanistic N management model called Maize-N. This model was unveiled at a plant nutrition symposium held in China in late 2008. The Maize-N model provides a platform for simulating indigenous N supply and for using long-term weather data to estimate attainable yield goal which together allow for the calculation of economic N rate needed to achieve a given level of yield potential. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: The majority of activities reported are targeted to the scientific community (i.e researchers in academic institutions). In the case of our regional evaluation of the Illinois soil N test, we have specifically targested the Crops and Soils article to Certified Professional Agronomists and Soil Scientists PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The completion of the beta version of the Maize-N model creates a link between edaphic and climatic information as they impact nitrogen use efficiency and physiological efficiency of N taken up by the crop. This model provides a mechanistic approach to residue decomposition and native soil N mineralization coupled to the mechanistic Hybrid-maize model to simulate the economic optimum N rate needed to supplement indigenous N supply to achieve temperature, radiation and water limited attainable maize yield. This model will be tested in Asia, N. and S. America at a number of sites during the 2009-10 maize seasons. If successful it will provide a common platform for resource allocation regardless of global location. Next, the completed and published report on the efficacy of the Illinois soil N test has shown that this test is extremely unreliable as a diagnostic tool for indigenous soil N and should be abandoned. The results of the long-term incubation of 15Nlabeled soil provides us with a very important look as where labile N is stored in soil organic matter and the relationship between soil C and N as it is transformed over time. We have found that MHA undergoes intensive cycling and that the N in MHA is a labile form of N that is used under immobilizing conditions. Originally we hypothesized that CaHA was a chemically protected form of humic acid that was well condensed as shown by its relatively old C mean residence time. However, under an intense and long-term N immobilization regime (i.e the addition of high C:N ratio plant residues), a portion of CaHa is mineralized with depletion of the mass of the CaHA pool over time. This was evidenced by the change in 14C MRT of approximately 100 to 200 years older after incubation and a loss of about 100o mg/kg of CaHA mass. It is apparent that there is a continuum of different aged CaHA that contributes to the overall pool age. Under conditions of intense immobilization pressure, the most recently formed and more labile CaHA is a donor of nitrogen for residue decomposition.
Publications
- Laboski, C., J.Sawyer,D.T.Walters, L.Bundy, R.Hoeft, G.W.Randall, and T.W. Andraski. 2008. Evaluation of the Illinois soil N test in the North Central Region of the U.S.. Crops and Soils: 4(3):11-14
- Laboski, C., J. Sawyer, D.T. Walters, L. Bundy, R. Hoeft, G.W. Randall, and T.W. Andraski. 2008. Evaluation of the Illinois soil N test in the North Central Region of the U.S. Agron. J. 100: 1070-1076.
- Amos, B., S. Madhavan., D.T. Walters, and T. Arkebauer. 2008 'Measuring Stable Carbon Isotope Ratios of Small Samples of Soil Respired Carbon Dioxide in a Maize-Soybean Rotation', Comm. in Soil Science and Plant Analysis, 39:9, 1321-1331.
- Wingeyer, A., and D.T. Walters. 2008. Quantitative analysis of the change in humic acid N storage under conditions of intense N immobilization. Paper presented at the Soil Science Society of America annual meeting. Oct 5-8, Houston, TX.
- Yang, H., T. Setiyono, D. Walters, K. Cassman, and A. Dobermann. 2008. Maize-N model: A systematic and mechanistic approach for N fertilization recommendations to maize. Proceedings of the International symposium on Plant Nutrition Management. Oct 18-20, Nanchang, China.
- Walters, D., A. Dobermann, M.A.A. Adviento, K. Cassman, T. Arkebauer , A. Liska, J. Specht, and H. Yang. 2008. Ecological Intensification of Corn-based Cropping Systems. In. L.S. Muphy (ed) Proceedings of the 2008 Fluid Forum, Feb, 17-18, 2008, Scottsdale, AZ.
|
Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: Several outputs have occurred for this project this year. In Nebraska, a thesis was completed as were several presentations at regional, national and international venues. Four refereed manuscripts were published as well. Fundamental research on the transfer of carbon and nitrogen among the selected soil organic matter pools was conducted and presented at the above mentioned meetings. The NC1032 Committee met in March of 2007 in Kansas City, Missouri to share results of progress toward the three project objectives. The decision was made to submit a proposal to the NRI Soil Processes Program but we were unsuccessful. A protocol was published whereby the procedures for conducting field measurements of uptake and N efficiencies in maize will be conducted. These procedures were approved by the members of the committee for application in the 2007 growing season. A central database will be made of data collected under objective 3 for dissemination to the NC1032 Committee for
analysis.
TARGET AUDIENCES: Target audiences: the majority of persons that have been presented the output of this project to date have been of the scientific community. However, summaries of the data generated herein has also been presented to members of certified crop consultant groups (approx. 400) during the past year.
Impacts
The results of several studies conducted under the NC1032 project were completed in 2007 and published in refereed journals or presented in scientific venue. A study was conducted whereby 15N-labeled soil from two intensively managed maize and maize/soybean sites was prepared for a long-term incubation. Two crop rotations were sampled: 1.) continuous corn and 2)corn-soybean and soybean-corn for two entry points in the rotation sequence. Prior to incubation, three residue treatments were added to soil: maize stover (23.7 mg N - 1770 mg C/ kg soil ); soybean leaves (23.7 mg N - 290 mg C / kg soil), and no residue added. Soils were analyzed at pre- and post-incubation times for light fraction (LF), mobile humic acid (MHA) and and calcium humate (CaHA ). A periodic leaching of the soil was performed and the leachate was analyzed for N and 15N atom%. Pre- and post-incubation whole soil (WS), LF, MHA, and CaHA fractions were analyzed for %C, %N, delta-δ13C and 15N atom%.
Post-incubation, all SOM fractions had a significant loss of 15N mass across treatments. The relationship between the change in 15N mass loss and N mass for each fraction indicated CaHA as a N donor fraction, and MHA and LF as both N donors and acceptors. Both LF and MHA had a high degree of turnover. The composition analysis of CaHA mass loss indicated this fraction is composed of materials with different degree of stabilization, and the released compounds are N-rich compared to the bulk CaHA pool. The LF %C4-C was significantly affected by both rotation and added residue. Post-incubation %C4-C significantly increased under maize ammendment, indicating LF as the primary pool for the C pathway into SOM fractions. This study indicates that the path of C and N flux from Residue > LF > MHA > CaHA, can be modified to CaHA > MB > MHA > LF under high N demand (immobilization environment) during decomposition of high energy C added to soil. Both humic fractions constitute N sources to LF and
residue decomposition, but MHA undergoes more rapid recycling of N and C. These findings identify the LF and MHA fractions as key in the movement of C into more recalcitrant, chemically stabilized soil organic matter fractions. Other studies were published which identified the impact of crop management on the sequestration of soil N and C. In the same study that supplied samples for the organic matter incubation studies reported above, we completed measurements comparing the global warming potential (GWP) of recommended and intensive (high yield) levels of management for both continuous corn and corn-soybean ratiations. Measurements included net-changes in soil organic carbon , intrinsic C costs associated with crop production (i.e. fossil fuel use), and net emissions of greenhouse gases (nitrous oxide and methane). Results indicate that intensification of cropping does not necessarily increase GHG emissions and the GWP of agricultural systems provided that crops are grown with best
management practices and near yield potential levels where resource use efficiency is high.
Publications
- Walters, D.T., S. Verma, A. Dobermann, K. Cassman, D. Ginting, A. Suyker, H. Yang and M.A.A. Adviento-Borbe. 2007. Carbon sequestration and global warming potential of continuous corn and corn/soybean rotations: Reconsidered. Abstracts of the 2007 International meeting of the Soil Science Society of America. Nov.4-8, 2007 New Orleans, LA
- Wingeyer, A.W. and D.T. Walters. 2007. Nitrogen cycling among soil organic matter fractions in agricultural systems. Abstracts, 2007 International meeting of the Soil Science Society of America. Nov.4-8, 2007 New Orleans, LA.
- Amos, B., S. Madhavan, D. T. Walters and T. Arkebauer. 2008. Measuring stable carbon isotope ratios of small samples of soil-respired CO2 in a maize-soybean rotation. Comm. Soil Sci. and Plant Anal. 39: In press
- Adviento-Borbe, M.A.A., M.L. Haddix, D.L. Binder, D.T. Walters and A. Dobermann. 2007. Soil greenhouse gas fluxes and global warming potential in four high yielding maize systems. Global Change Biology 13:1972-1988
- Grant, R.F., T. J. Arkebauer, A. Dobermann, K.G. Hubbard, T.T. Schimelfenig, A.E. Suyker, S.B. Verma and D.T. Walters. 2007. Net biome productivity of irrigated and rainfed maize-soybean rotations: Modeling vs. Measurement. Agron. J. 99(6):1404-1423
- Amos. B., Hui Shen, T. Arkebauer and D.T. Walters. 2007. Effect of previous crop residue on soil surface carbon dioxide flux in maize. Soil Science 172(8):589-597
- Dobermann, A., D.T. Walters and M.A.A. Adviento. 2007. Global Warming Potential of high-yielding continuous corn and corn-soybean rotations. Better Crops, 91(3):16-19
- Wingeyer, A.W. 2007. The effect of residue C:N ratio on the turnover of N and C in various soil organic matter fractions. MS thesis University of Nebraska-Lincoln
|
|