Brief Summary of Minutes of Annual Meeting

1. Determine the roles of innovative management practices, the environment, and their interactions on optimum use of nitrogen in agroecosystems.

Short-term Outcomes:

Across multiple locations, Jagadamma and Poffenbarger found that legume and mixture cover crops did not have a significant impact on the optimum N rate of corn. However, Norton found that hairy vetch contained about 110 kg N/ha in aboveground biomass, and estimated that it would provide about 55 kg N/ha to the subsequent corn crop. In a multi-state coordinated study, Poffenbarger found that cereal rye significantly increased the optimum N rate of corn by over 50 kg N/ha. In a laboratory study, Saha found that increasing drying-rewetting intensity of the soil increased N₂O emissions and that the presence of cover crop residue reduced the N₂O emissions under extreme drying-rewetting.  

In field research studies evaluating different nitrogen fertilizer sources, Yin found that non-stabilized dry urea and broadcast UAN produced high ammonia volatilization. Adding ANVOL, a urease inhibitor, reduced ammonia volatilization with all surface-applied urea and UAN treatments. In addition, ANVOL increased corn grain protein numerically and grain yield +4 to +13 bu/Ac when added to UAN in the row middle (dribble), UAN Y-drop, UAN broadcast, or urea broadcast N. Urea + ANVOL yielded statistically similar in corn as potentially higher cost specialty urea products such as ESN and SuperU.

Arnall has been summarizing 20 years of approximately 100 site-years of winter wheat N rate and timing work in Oklahoma, finding that the optimum timing of N application for wheat was at the Feekes 6 stage. While developing N uptake curves for low and high protein varieties, he determined that low protein wheat accumulates a larger proportion of N by anthesis than high protein wheat.

Horwath found that microirrigation systems (surface or subsurface drip) substantially decrease N₂O emissions from the soil as compared to flood irrigation systems.

Outputs:

Over the past year, our group has produced three peer-reviewed publications and five presentations about how cover crops affect soil N cycling. The group has also presented about enhanced efficiency nitrogen fertilizers and their impact on ammonia volatilization loss (one presentation).

In addition, several graduate students and undergraduate students have been trained in these projects, and more outreach is planned to share these results. Norton is planning to use data collected on the N contribution of vetch cover crops to corn to make adjustments for N recommendations in Utah.

Activities:

In 15 states across the U.S., researchers are conducting a coordinated study to determine how legume, cereal rye, and rye-legume mixtures affect the optimum N rate for corn as compared to no cover. This study will continue for two more years.

In Tennessee, Jagadamma has been studying how cover crops (wheat, crimson clover, wheat-clover mixture, a five-species mixture of wheat, oats, crimson clover, hairy vetch, and daikon radish) affect N fertilizer needs of the subsequent corn crop as compared to no cover.  Through periodic soil and plant sampling, and the use of resin membranes in-situ, the project will determine if producers can reduce N application to corn by growing winter cover crops and if so, which cover crop species is most suitable for providing N credits to corn.

In Tennessee, Saha has been studying how cover crops affect soil N₂O emissions, particularly under increased rainfall variability caused by climate change. A laboratory incubation was conducted to examine cover crop roles in N₂O emissions from N fertilized soils when exposed to different rewetting-drying intensities. These factors included i) cover crop residue (3 levels): no cover crop, winter wheat, and crimson clover, ii) rewetting intensity (2 levels): 70 and 90% water-filled pore space (WFPS), and iii) drying intensity (2 levels): 10 and 40% WFPS. Urea fertilizer with or without dry cover crop residues were mixed in repacked soil cores. The group measured N₂O, CO₂ fluxes, and N₂O isotopomer composition and soil biogeochemical variables. Saha is also leading an effort to quantify tillage, cover crop, and nitrogen fertilization effects on O₂ and N₂O fluxes in the field, and to develop a machine learning modeling approach for N₂O prediction using soil O₂ and other biogeochemical variables as predictors.

Also in Tennessee, Yin has been studying how different fertilizer sources, methods of application, and enhanced efficiency products affect ammonia volatilization and corn yields.

In Oklahoma, Arnall is completing the final analysis and summation of three years of a large scale corn nitrogen rate by water rate study. A focus of this project is the evaluation of spatial and temporal variance. A thesis and peer review publication will be completed in 2022. In addition, Arnall is developing nutrient uptake curves of known low protein and high protein wheat cultivars and implementing a winter wheat study that will evaluate the potential for a relationship between genetic background and optimum nitrogen fertilizer timing.

2. Understand the role of soil biological processes in controlling plant available nitrogen and their relationships with soil health and system resilience.

Short-term Outcomes:

McDaniel, in collaboration with Drijber and their students, staff and faculty colleagues have been studying soil biological properties in the rhizosphere and bulk soil of corn fields. The team has found that diversified crop rotations dampen the rhizosphere effect and decrease the effect of corn roots on soil microbes and carbon in particular as compared to short crop rotations. The lower allocation of carbon to roots in the long rotation may help to explain why corn performs better in the long rotation.

Laboski found that measurements of POX-C and ammonium collected at planting were good predictors of the economic optimum N rate of corn and performed better than the current recommendation system, the maximum return to N.

Horwath found that composts and cover crops did not lead to significant carbon sequestration in California, or improvements in crop yield.

Outputs:

The group has produced four peer-reviewed publications and two presentations about the effects of management on soil health and soil biological processes.

Activities:

Drijber Initiated and sampled soil from three collaborative field experiments this past year for assessment of soil microbial community impacts (particularly on arbuscular mycorrhizal fungi) from a variety of crop and soil management practices:

1. In collaboration with Brian Arnall from Oklahoma State University (NC1195 committee member) we sampled his ongoing field trails for winter wheat and sorghum to evaluate the impact of delayed N fertilization on the soil biomass and seasonal dynamics of arbuscular mycorrhizal fungi, an important contributor to plant nutrient uptake and soil C sequestration.
2. The second study revisited UNL’s Roger’s Memorial Farm four years after conversion of all tillage plots to no-till and introduction of cover crops to evaluate recovery of no-till soil microbial communities and soil health parameters.
3. In collaboration with the USDA-ARS group in Lincoln, NE, we also had the opportunity this spring to soil sample Galen Erickson’s long-term cattle grazing trial comparing fertilized, supplemented and control paddocks for soil health measures, N-cycling genes and soil microbial communities.
4. Continued our research into biochar impacts on soil microbial communities and soil health parameters.

McDaniel and Drijber, along with graduate students and other faculty colleagues are studying corn rhizosphere dynamics in long and short crop rotations to explore whether differences in rhizosphere dynamics could explain better corn yield in long rotations.

Norton and her undergraduate students sampled vetch shoots and roots with nodules before termination and investigated nitrogen fixing bacteria from these samples. Several nodule occupants were isolated and chosen for draft genome sequencing. All were closely related to Rhizobium leguminosarum. Refinement of sequences and further characterization of biological N fixation by vetch cover crops continues.

McDaniel and Laboski have been compiling data from members of the NC1195 committee to understand the relationship between soil health indicators and the economic optimum N rate of corn.

3. Translate field and laboratory research into nitrogen management decision-making tools and educational resources promoting improved profitability and sustainability of corn-based cropping systems.

Short-term Outcomes:

To engage students, the general public, growers, and crop advisers in learning about nitrogen cycling in Iowa agricultural systems and nitrogen reduction strategies, we used teaching and learning materials that were created in 2019-2020. This included a user-friendly, process-based simulation model of nitrogen cycling in agricultural systems and the accompanying instructional materials. The learning materials were used in undergraduate ecology courses, 45 students at ISU and 50 at Lake Superior State University. Since its inception in 2020, the website has had ~600 page views and 150 downloads.

Yin determined that the reference N sufficiency range for corn at the seedling stage is too low for current cultivars, while the ranges at tasseling and maturity are too high. These will need to be modified with further research.

Outputs:

Instructional materials about nitrogen cycling in agricultural systems were hosted on this website, https://nmodel.nrem.iastate.edu/, and published.

The group has produced three extension or outreach presentations in the last year, and also one newsletter article for producers about cover crop effects on optimum N fertilization practices.

Activities:

In Iowa, Russell has been developing learning modules and case studies for students and producers using an open-access platform called Gala. The platform allows others to provide comments before finalizing the modules.

Li used Monte Carlo simulations and on-farm experiments to evaluate the economic performances of different trial designs in site-specific nitrogen rate recommendations, and identified the most profitable trial design selection for on-farm nitrogen experiments.

Khanal is using remote sensing to understand cover crop presence, biomass, and impact on cash crop yield across large areas of Western Lake Erie Basin.

Several group members including Li, Khanal, Saha, and Poffenbarger are using or interested in using machine learning tools to translate large datasets into predictive tools that could be used to inform farmer decision-making.