Progress 04/15/16 to 04/14/21
Outputs
Target Audience: Farmers, other agricultural professionals, extension and NRCS personnel, soil health and IPM practitioners, soil scientists, agronomists, and other agricultural scientists. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided training and professional development opportunities for two graduate students, one in the Tooker lab and one in the Kemanian lab. The graduate students lead the experiments and also engaged in scientific meetings as part of their professional development. In each field season from 2017-2020, the project also provided training opportunities for a total of four undergraduate student research assistants. How have the results been disseminated to communities of interest?Our results have been shared with audiences via presentations by the two graduate students and one undergraduate. These presentations occurred at formal and informal meetings at: 2018 ASA, CSSA, and CSA International Annual Meeting Penn State University Department of Plant Science. 10 April 2020. Gamma Sigma Delta Research Expo at Penn State University. 24 March 2020. Cancelled due to COVID-19. Schlow Centre Regional Library Research Unplugged. 2019 May 2. 2017 Annual Meeting of the Entomological Society of America. 2018 Joint Annual Meeting of the Entomological Society of America and Entomological Society of Canada, Vancouver, BC, Canada, November. 2019 Annual Meeting of the Entomological Society of America 2020 Agronomy Society of America/Crop Science Society of America/Soil Science Society of America) International Annual Meeting. Virtual Student Competition e-Poster and Presentation Sustainable Agronomy Conference. Virtual Student Competition. Aug. 19, 2020. Dept. of Plant Science, The Pennsylvania State University, 25 February 2021. Dept. of Entomology, The Pennsylvania State University, 20 May 2021 (scheduled). What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Interspecific polycultures: We completed analysis of the following data sets that were assembled in the dissertation of Amanda Burton (PSU, Plant Science, Agronomy). Each one of the items below is a chapter summary: 1) We reviewed literature from the early 1920s until recent years to characterize yield of silage maize and mixture of maize and soybean. We discovered more than 300 cases pairing pure plots and mixtures worldwide, extracted values for mean and variance to compile a meta-analysis dataset that we analyzed using non-parametric statistics. The main outcome is that if maize population is kept at or above 5.3 plant per m^2, then the yield of the mixtures is similar to that pure maize. There is a clear technology signal, with yields increasing with time, reflecting progress in plant breeding for great productivity. There is also a bimodal distribution in interest in mixtures, which was relatively high early in the 20th century, subsided in the middle of the century, and somewhat reignited after the 1980s.The resulting paper will be submitted to the Italian Journal of Agronomy. 2) One of the main experiments testing mixtures of maize, sorghum, soybean, and yet another mixture with sunflower for three years, was analyzed and published in the Agronomy Journal [Side note: the paper was selected for a highlight to be presented in the CSA News in June or July. The CSA News is a magazine distributed among members of the tri-societies that highlights original contributions published in the societies' journals] Even though we did not experience a year of severe water stress, where we expected sorghum to compensate for yield losses in maize, we found that: i) mixtures of sorghum and maize yielded as much maize, and may increase potash concentration it the silage; ii) the addition of soybean to maize, even in very low densities, increases the protein content of the mix; iii) mixtures with sorghum seem to leave less residual mineral nitrogen in the soil post harvest, preventing future leaching; iv) even though some mixtures did not elicit a yield penalty, there were practical challenges to establishment and for weed control that need further research. 3) We modeled yield and water use of maize, sorghum, and maize/sorghum mixtures for the continental United States using the model Cycles. Cycles is a multi-year, multi-species, daily time-step agroecosystems model developed in part by co-PI Kemanian. We used a single representative soil and weather record (1979-2018) per county (more than than 3,000 counties) to simulate rain-fed productivity. We discovered that mixtures of maize and sorghum are suitable for the area currently known as the sorghum belt, which lies south of the Dakotas and extends south toward the Texas panhandle, occurring essentially along the 100th meridian. Further improvements are needed to represent soils as seen by the plant roots (meaning, to represent limitations to root growth). A specific product of this project is that we developed a tool to test in silico what can be difficult to test experimentally. The paper resulting from this effort will be submitted to Agronomy Journal, or possibly the European Journal of Agronomy. We completed analysis of the following data sets that are currently being assembled in the dissertation of Julie Baniszewski (PSU, Entomology) Intraspecific polycultures: We evaluated in a three-year study in Pennsylvania the performance of a four-cultivar mixture of wheat and its constituent sole cultivar stands. To measure costs and benefits of intraspecific diversity under field conditions, we assessed the influence of cultivar mixtures and sole cultivar stands on diseases, insect pests, arthropod predation, and yield. We also compared the economic and environmental value of cultivar mixtures and sole cultivar stands by determining how they perform in presence and absence of insecticide and fungicide applications. We hypothesized that, compared with sole cultivar stands, cultivar mixtures of wheat will provide 1a) greater arthropod predator abundances and 1b) therefore, higher rates of predation on pest species; 2) lower disease incidence; and 3) higher and less variable yields. Compared to chemically treated sole cultivar stands, we also hypothesized that wheat mixtures that did not receive pesticides would have similar economic value and greater benefits from natural enemy-driven ecosystem services. Contrary to our expectations, considering the contrast test for all years combined and the "by years" analysis, the cultivar mixture did not host higher predator abundances, nor did it foster higher rates of predation compared to sole cultivar stands. A lack of herbivores is the most reasonable explanation for similar abundances of natural enemies in the mixture compared to sole cultivar stands - the mixture did not provide a direct increase in predaceous arthropods. Although we did not see higher rates of predation in the cultivar mixture compared to sole cultivar stands, our study demonstrated the harmful effects of non-selective insecticides on natural-enemy populations. As expected, at all time points, insecticide-sprayed plots significantly reduced lady beetle abundances. In contrast to our results with insects, the cultivar mixture suppressed foliar disease of wheat. Moreover, lower disease incidence correlated with cultivars that had higher ratings of foliar disease resistance. The mixture had overall lower disease incidence (22 ± 2%) and low variance among plots indicating that it limited disease spread by either dilution or by slowing the rate of transmission. As expected, the fungicide application reduced foliar disease; there was about 18% decrease in disease from the fungicide application over all three years. Although the mixture only reduced foliar disease by 5% compared to the overall sole cultivar stand three-year average, there was 25% less foliar disease in the mixture (22%) compared to the most vulnerable variety. Because the cultivar mixture and fungicide application independently suppressed foliar disease and we did not detect a significant cultivar * pesticide interaction, we found that a mixture of wheat without fungicide applications can indeed provide similar levels of control as chemically treated sole cultivar stands. Notably, the cultivar mixture yielded similarly to sole cultivar varieties. The 2.6% increase we saw from mixtures, although not significantly in our study, was similar to other studies and meta-analyses which show 2.2-3.5% overyielding with mixtures. Similar to the outcome of their yields, the mixture neither harmed nor improved the economic benefit compared to sole cultivar stands. The return over variable costs was affected only by year. However, the lack of economic significance is important because it highlights that neither cultivar treatment nor pesticide applications had higher economic value over the three years of the study. Environmental differences among years had a much larger impact than fungicides, insecticides, or mixing cultivars. In other words, the yield increase associated with the pesticides had no economic value beyond simply paying for the chemicals. Furthermore, the disease suppression from the cultivar mixture is particularly promising because the mixture we constructed did not target any specific pathogens, yet it performed well against those that colonized our fields. If wheat cultivars were better characterized so that mixtures could be constructed with specific pathogens (or other biotic or abiotic stresses) in mind, the benefits of mixtures would likely be even greater.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Burton, A. B., J. Baniszewski, G. W. Roth, J. F. Tooker, and A. R. Kemanian. 2021. Are polycultures for silage pragmatic medleys or gallimaufries? Agronomy Journal, in press. DOI: 10.1002/agj2.20602
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Baniszewski, J, A. Burton, A. R. Kemanian, G. W. Roth, and J. F. Tooker. 2021. Wheat intraspecific diversity suppressed diseases with subdued economic and ecosystem services benefits. Agriculture, Ecosystems and Environment, in press.
- Type:
Theses/Dissertations
Status:
Submitted
Year Published:
2021
Citation:
Burton, A. B. Thwarting climate change using simple practices in complex and adaptive agricultural systems. Ph.D. Dissertation, Dept. of Plant Science, The Pennsylvania State University. May 2021.
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Progress 04/15/19 to 04/14/20
Outputs
Target Audience: Farmers, Extension staff, agronomists, other agricultural professionals, entomologists Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided training and professional development opportunities for two graduate students, one in the Tooker lab and one in the Kemanian lab. The graduate students are leading the experiments and have also engaged in scientific meetings as part of their professional development. In 2019, the project also provided training opportunities for three undergraduate student research assistants. How have the results been disseminated to communities of interest?Three talks were submitted on this topic. Two were delivered, but one was canceled due to the COVID-19 quarantine guidance in place. A manuscript focusing on silage yield, nutrient composition, and soil nitrogen is in progress and near ready for submission to a journal. We have also drafted a manuscript assessing performance of the wheat cultivars for insect and disease control, and anticipated submitting it to a journal mid 2020. A review paper exploring the use of corn-based silage polycultures is also in-progress. This review paper is anticipated to be submitted to a journal by September of 2020. A third paper covering the water exclusion experiment is in draft form and is anticipated to be sent to a journal in mid-2020. Field data will be used to create/calibrate models aimed at exploring the feasibility (yield) of using silage polycultures across temperature and precipitation gradients within the United States. What do you plan to do during the next reporting period to accomplish the goals?Much of our effort in the past years has been focused on collecting data from our eight field seasons (three wheat seasons running from October - July; and four seasons of mixtures of corn, soy, sorghum, sunflower, running from June through October). Now that we are nearly done with gathering data and compiling all that we have collected, we will be working with our students to use all the data to model the response of our two polyculture systems to biotic and abiotic stress. The third objective of our project is to "Measure and model the response of mixtures and monocultures to water stress to discern whether within stand variability can mitigate this abiotic stress." In the final year of our project we will work to properly complete this objective.
Impacts
What was accomplished under these goals?
Silage In the past year, we have continued to assess biotic advantages of silage mixtures compared to monocultures. Methods and results were very similar to the previous years. We evaluated the foliar arthropod community using sweep netting and ground arthropods using pitfall traps once monthly. Overall, we found that split plots that were treated with insecticides had a much stronger influence on arthropod populations than the species mixtures--of course insecticides decreased arthropod populations, but contrary to our hypothesis species mixtures did not significantly increase arthropod populations. We found a similar trend with arthropod predation, with sprayed split-plots having much less predation compared to control plots regardless of species mixture. Although mixtures appeared to provide some minor benefits for predation and increases in arthropod diversities, the greatest benefit we detected was fostering the resident arthropod population and not decreasing it via insecticides. Disease, particularly foliar disease, was somewhat decreased by mixtures, but disease pressure was relatively low. Mixtures with corn and sorghum had greater nitrogen deficiencies than monocultures or mixtures with soybeans. This could was not apparent in 2019 with additional nitrogen. Total biomass was similar in all plots except soybean monocultures, which grew significantly less biomass . Relative biomass (i.e., the biomass produced in mixtures based on the monoculture population) was higher for all crops indicating some benefit at the plant level when each species is grown in a mixture than on its own. Quality analysis showed slightly higher crude fiber in forage treatments with sorghum. However, mixtures had higher economic value because of the similar yields from corn and sorghum biomass with the additional high value soybean protein and sunflower oil. We performed a water exclusion experiment as an offshoot of the main silage project, and used maize and sorghum polycultures, as well as a maize + sorghum + soy + sunflower polyculture. In this experiment we attempted to force water stress by covering the interrow space with polycarbonate panels and measure the resulting plant stress. Water use and soil water content under open and covered conditions was measured using a capacitance soil probe. Water potential readings were taken twice--once after a heavy rain and once after a period of drying--to assess the soil water content in each plot. Aboveground biomass was harvested in early September at the stage when silage would be harvested. Grain was separated from maize and harvest indices calculated. Wheat We completed the third and final year of the wheat component in 2019. To evaluate the arthropod community, we assessed weekly arthropod populations using sweep netting. Pest populations were low, so we only monitored lady beetle populations because they were the most abundant predator. Some cultivars had higher abundances of lady beetles than others and the mixture of all four cultivars hosted an average abundance of lady beetles. We used aphid sentinel prey traps to evaluate foliar predation about once monthly. We found that predation in the mixture of cultivars was about average compared to predation the monocultures. Similar to the forages, control split plots had much greater abundances of arthropods, including lady beetle predators as well as much higher rates of predation, confirming that indiscriminant insecticide applications strongly and negatively influence beneficial arthropod populations. Both foliar and head disease were monitored weekly after wheat heading. Mixtures suppressed foliar diseases comparable to that of a fungicide application, but had less impact on head diseases. The split-plot sprayed with fungicide had noticeably less disease than the control plots. DOM vomitoxin analysis after harvest showed that fungicide-sprayed plots as well as some of the resistant cultivars had slightly lower values of vomitoxins. Yields were slightly higher with some cultivars, but similar in the insecticide/fungicide splits, suggesting that there is little benefit for productivity to indiscriminate insecticide/fungicide use. Furthermore, economic analysis showed the chemically treated split-plots had no additional economic benefit than without in the control split plots, and was therefore only enough to offset the cost of spraying. In years with low disease pressure, it is likely the non-sprayed wheat would have more economic value, however, disease and weather are unpredictable. Results indicate that the wheat mixture was able to suppress disease, specifically foliar disease with similar yields and no effect on predator or arthropod communities. Consequently, wheat mixtures may be a solution for highly unpredictable environments. In 2018, NDVI measurements were made weekly until senescence. Three biomass harvests were taken: one at tillering, one at flowering, and one at harvest. Harvested material was dried and total aboveground biomass--as well as total grain yield at harvest--was calculated. Biomass tissue was ground and assessed for elemental composition. Soil cores (0-20 cm and 20-40 cm) were collected both at the beginning of the season and post-harvest. Cores were analyzed for nitrate and ammonium content as well as gravitational water content. Modeling The simulation model Cycles was modified to represent silage management with greater fidelity and ease. Corn and sorghum, as well as cover crops sometimes included in rotational systems, respond different to clipping. Corn acts like an annual plant that when harvested for silage essentially dies (no "ratooning"). Sorghum instead expresses it perennial origins and can regrow unless a frost kills it. Many cover crops can regrow after a clipping. The model included options before to kill a crop on a calendar basis (fixed date) that sometime would not match with the phenology (or harvest date), or after a grain harvest. We added the option to kill a crop after harvest, and to select the fraction of stove or grain that could be harvested. Thus, the system can now simulate a large array of complex management practices representing with more fidelity rotational systems that include silage.
Publications
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2020
Citation:
Burton A. Are polycultures for silage medleys or gallimaufries? Talk presented at: Penn State University Department of Plant Science. 10 April 2020.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2020
Citation:
A. Burton, J. Baniszewski, J. Tooker, G. Roth, A. Kemanian. Are polycultures for silage a robust sm�rg�sbord or motley cow chow? Accepted and to be presented at Gamma Sigma Delta Research Expo at Penn State University. 24 March 2020. Cancelled due to COVID-19.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2019
Citation:
Burton A. Climate Resilient Agriculture. Talk presented at: Schlow Centre Regional Library Research Unplugged. 2019 May 2.
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Progress 04/15/18 to 04/14/19
Outputs
Target Audience: Farmers, Extension staff, agronomists, other agricultural professionals, entomologists ? Changes/Problems:We plan to conduct the same weekly and monthly protocols in 2019 as we have previously. We've adjusted populations, row spacing and varied equipment uses to best accommodate logistics as farmers may do. The largest problem we've encountered is having low overall arthropod pest populations, which may have masked potential differences in mixtures. We've taken some of our findings and applied these to more specific studies tailored at finding optimal populations and better understanding how species mixtures may alter or suppress weed communities. What opportunities for training and professional development has the project provided?To complement the current objectives, we have designed a similar project looking at how mixtures may suppress certain weed seeds as well as attract certain weed seed predators. We are also working with an undergraduate student interested in forage mixtures and if a higher or lower population of four-species may produce higher yields as well as weed seed size preference by arthropod predators. We have used this project as an opportunity to develop extension skills by showing the field on farm tours, talking at extension meetings and field days and working with undergraduate students who are interested in agriculture, entomology and ecology. Finally, we have also found that logistics are much more complicated with mixtures of different species than monocultures because of seed size, equipment limitations and growth patterns. Corn seeds are too large to mix with sorghum, sunflower or soybean and need to be planted separately. Sorghum matures later than the other crops and is best cut after the first fall frost. How have the results been disseminated to communities of interest?Through extension meeting, field days and farm tours, we have engaged with growers who have been interested in planting some mixtures (i.e., corn and sorghum) for silage but have been "too afraid" to go through with it. Engaging with these farmers, we have been able to tell them that although there might not be an increase in biomass, by adding a little high-value crop such as soybean or sunflower to the mixture, crude fiber is increased and the economic value is increased. We've also learned from some farmers who have tried sorghum on its own, that cows prefer it mixed with something because sorghum alone has too much crude fiber. What do you plan to do during the next reporting period to accomplish the goals?In Fall 2018, we established another experiment of wheat cultivar mixtures and associated monocultures. We have been sampling these plots during spring and will harvest them for yield in July. In June 2019, we established our fourth year of a forage species mixture experiment. We will sample these plots for plant productivity, nitrogen and water use, arthropod populations and yield.
Impacts
What was accomplished under these goals?
Short-term project objectives focused on biotic communities and water and nitrogen-use efficiencies of mixtures of forage species and wheat cultivars compared to respective monocultures. Specific objectives included: Assessing foliar and ground arthropod community diversity and abundance. Assessing foliar and ground arthropod predation. Assessing disease incidence and nitrogen deficiencies. Assessing nitrogen and/or water use Collect data that is relevant for creating models to simulate the use of polycultures and mixtures across a temperature and precipitation gradient. Silage On a monthly basis, we assessed foliar arthropods using sweep netting and epigeal arthropods using pitfall traps. Split plots were sprayed with insecticides to understand the role of insect herbivores on plant productivity. These insecticide application had a much larger impact on reducing arthropods than the species mixtures. This was most evident in the foliar community which would have had direct contact with the foliar-sprayed insecticide compared to the ground dwelling arthropods. We found a similar trend with arthropod predation, with sprayed split-plots having much less predation compared to control plots regardless of species mixture. We also quantified fall armyworm (FAW) damage to corn and found mixtures had slightly less damage from FAW, likely because one cultivar of corn had a Bt trait against FAW. Although mixtures may have some benefit for predation or increase some arthropod diversities, the greatest benefit was not using chemical insecticides. Reduced insecticide sprays could come as a result of using mixtures, such as reducing major pests like FAW to below a threshold for spraying. Disease was somewhat inhibited by mixtures, but disease pressure was relatively low. Mixtures with corn and sorghum had greater nitrogen deficiencies than monocultures or mixtures with soybeans. This could be combatted with additional nitrogen, which we plan to apply to the 2019 season. Total biomass was similar in all plots except soybean monocultures. Relative biomass (i.e., the biomass produced in mixtures based on the monoculture population) was higher for all crops indicating some benefit at the plant level when each species is grown in a mixture than on its own. Quality analysis showed slightly higher crude fiber in forage treatments with sorghum. However, mixtures were valued higher economically because of the similar yields from corn and sorghum biomass with the additional high value soybean protein and sunflower oil. In 2018 we also collected early-season soil cores (0-20 cm and 20-40 cm) and end-of-season deep soil cores (~1 m). These soil cores were processed for nitrate and ammonia content, soil texture, bulk density, and gravitational water content. Additionally, deep core samples for 2016 & 2017 were analyzed for soil texture. In season, NDVI and photon flux density was measured to assess canopy closure. Water potential was measured using a pressure chamber. Unfortunately, we never had a dry period, so water stressed water potentials were unable to be taken. Two biomass samples were taken--one at flowering and one at harvest. Biomass was separated by species and dry yield was calculated. For harvest, this included separating corn grain from other above ground biomass. Biomass tissue was ground and analyzed for elemental composition. Wheat Using sweep nets, we monitored lady beetle populations weekly. Some cultivars had higher abundances of lady beetles than others and the mixture of all four cultivars was average. Monthly we used aphid sentinel prey assays to evaluate foliar predation and found the mixture of cultivars was average compared to the monocultures. Similar to the forages, control split-plots had much greater abundances of arthropods, including lady beetle predators as well as much higher rates of predation. Weekly after heading we monitored foliar and head disease. Disease was most inhibited by cultivars with disease resistant traits and intermediate in the four-cultivar mixture. The split-plot sprayed with fungicide had noticeably less disease than the control plots. DOM vomitoxin analysis after harvest showed that fungicide-sprayed plots as well as some of the resistant cultivars had lower values of vomitoxins. We took NDVI and temperature measurements weekly until senescence. Three biomass harvests were taken: one at tillering, one at flowering, and one at harvest. Dry matter was calculated. For the final cutting at harvest, grain yield was determined. Biomass tissue was ground and assessed for elemental composition. Soil cores (0-20 cm and 20-40 cm) were collected both at the beginning of the season and post-harvest. Cores were analyzed for nitrate and ammonium content as well as gravitational water content. Yields were slightly higher with some cultivars and slightly higher in the insecticide/fungicide splits. However, economic analysis showed the slight increase was only enough to offset the cost of spraying and had no additional benefit. In years with low disease pressure, it is likely the non-sprayed wheat would have more economic value. Disease and weather are unpredictable. Results from the wheat mixture show mediocre disease suppression and intermediate predator abundances, yield and quality throughout the three years of this study indicating wheat mixtures may be a solution for highly unpredictable environments.
Publications
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Progress 04/15/17 to 04/14/18
Outputs
Target Audience: Farmers, Extension staff, agronomists, other agricultural professionals, entomologists Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Our project has provide training and professional development opportunities for the graduate and undergraduate students that are implementing the research and collecting samples and data. Our plots have also been featured in tours of our research farms; attendees of such tours are agricultural professionals and farmers. How have the results been disseminated to communities of interest? We have shared results orally with visitors to field tours, and in scientific pressentations at the Annual Meeting of the Entomological Society of America and the Tri-Society meetings (The American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America) What do you plan to do during the next reporting period to accomplish the goals? In 2018, we will finishing collecting data in our intraspecific wheat experiment. We will also repeat both field experiments, both interspecific diversity with corn, sorghum, soybean, and sunflower, and intraspecific with wheat.
Impacts
What was accomplished under these goals?
We have yet to have meaningful impact because we are still collecting data from field experiments. In 2017 (like 2016), we establishedtwo experiments. We collected data on crop productivity (biomass, species composition), soil moisture, nitrogen concentrations in soil and plants, forage quality analyses, water stress, andinsect and beneficial arthropods communities among others.
Publications
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Progress 04/15/16 to 04/14/17
Outputs
Target Audience:Farmers, Extension staff, agronomists, other agricultural professionals, entomologists Changes/Problems:Our species mixtures made weed management a challenge, so we sought greater counsel from weed management colleagues in establishing our 2017 field experiment. In the 2016 experiment, we also detected similar arthropod populations and predation in our plots. This result may have stemmed in part from smaller plots than we would have like (30 x 70 ft) full plot), so this year we requested larger fields to accommodate slightly larger plots (50 x 80 ft) to try to better isolate insect populations in each (i.e. less movement between plots). What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?In 2017, we will finishing collecting data in our intraspecific wheat experiment. We will alsorepeat both field experiments, both interspecific diversity with corn, sorghum, soybean, and sunflower, and intraspecific with wheat.
Impacts
What was accomplished under these goals?
During the 2016 growing season, we established two field experiments. One that was established in May 2016 and used corn, sorghum, soybean, and sunflower to test the value of interspecific diversity for moderating biotic and abiotic stress. The other was established in October 2016 to test the value of intraspecific diversity for moderating similar stresses in wheat. We have collected a suite of data for the interspecific diversity experiment, but are still in the process of collecting data in the wheat experiment. I will characterize our efforts in the interspecific diversity experiment. We quantified stand establishment and biomass production in each plot. We sampled plant water potential at dawn and at noon, to characterize the response to a dry spell. We also sampling insect pest and natural enemy populations. We found that the sorghum produced the highest biomass yield, followed by corn alone, and the corn/sorghum mixture. Yield in the four-way mixture (corn, sorghum, soybean, and sunflower) reflected the proportion of each species, as did the corn/soy mix. We have yet to analyze yet the samples for nitrogen in the harvested biomass (they are ready to go to the lab), but result may vary when comparing to biomass due to the higher concentration on N in the soybean tissue. As expected, we detected more intense interspecific competition when exploring corn productivity via the harvest index (HI). When growing pure, corn HI was around 0.55; in the four-way mixture corn HI = 0.42, reflecting strong flowering and post-flowering stress, and when growing with sorghum about 0.45, again reflecting competition. One-meter deep soil cores taken from each plot after harvest revealed that the plots with largest biomass had the lowest residual nitrogen in the profile. The highest residual N was in the soy plots at 107 kg/ha residual N, followed by corn (95 kg/ha), corn and soybean (88 kg/ha), corn and sorghum (74 kg/ha), mixture (69 kg/ha) and sorghum alone (56 kg/ha). The higher tolerance of sorghum during the dry season and the leafiness compared with corn seemed to allow a higher accumulation of nitrogen and much lower risk of post harvest leaching. All soil profiles in each plots have been described to support modeling efforts. Preliminary model runs with the model Cycles of mixtures of corn and soybean or corn and sorghum indicate that, in terms of biomass, the mixtures seem to produce a plant-density weighted average of the biomass of each crop in a pure mix. As indicated before, this result may differ for nitrogen and perhaps for the mineral nitrogen quantity and distribution in the soil. For our insect sampling, sweep netting for pest species revealed a significant reduction in pests with increasing crop species diversity (number of species) but a inconsistent differences among crop mixtures. Predator populations (abundance and diversity) were not significantly different between any crop mixtures. We detected no significant difference in pests or predator abundances or predation as measured by sentinel prey assays in our split plots where insecticides were sprayed or not. - Overall predation on waxworm sentinel prey traps were high for all crop mixtures and indicated no difference in predation between crop treatments. There was an insecticide by species diversity interaction that indicated higher predation was present in non-insecticide monocultures but shifted to higher predation with insecticide in the two species mixtures and was equal in the four species mix across the split insecticide treated plots.
Publications
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