Location: Agroecosystems Management Research
2022 Annual Report
Objectives
Objective 1: Quantify the effects of conventional and alternative corn-soybean based cropping systems on the factors and processes of nutrient cycling and nutrient-use efficiency. Sub-objectives: 1.1 Determine effects of conventional and alternative corn-soybean based cropping systems on soil nutrient dynamics and crop nutrient uptake and yield; and 1.2 Determine effects of organic cropping systems on soil carbon and nitrogen storage.
Objective 2: Evaluate the effects of conventional and alternative corn-soybean based cropping systems, on soil water dynamics and drainage water nutrient transport. Sub-objectives: 2.1 Determine effects of fall-planted cover crops and no-tillage within conventional and alternative corn-soybean rotations on tile flow and drainage water nutrient concentrations; and 2.2 Determine effects of organic cropping systems on water quality and soil profile water storage.
Objective 3: Determine the effects of conventional and alternative corn-soybean based cropping systems, on indicators of soil health. Sub-objectives:
3.1 Determine effects of organic cropping systems on soil health; and 3.2 Determine effects of fall-planted cover crops, relay crops, and no-tillage within conventional and alternative corn-soybean rotations on soil health.
Objective 4: Operate and maintain the Upper Mississippi River Basin Experimental Watersheds LTAR network site using technologies and practices agreed upon by the LTAR leadership. Contribute to the LTAR working groups and common experiments as resources allow. Submit relevant data with appropriate metadata to the LTAR Information Ecosystem. Goals: 4.1 Implement the LTAR Common Experiment comparing conventional (BAU) and aspirational (ASP) cropping systems and the measurement of parameters to support analysis of sustainability and ecosystem services for these cropping systems; and 4.2 Develop improved capabilities for acquiring, storing, and providing data to the LTAR Network and the larger agricultural community.
Approach
A combination of controlled experiments in the field and laboratory, tile drainage monitoring, and a variety of modeling techniques and statistical analyses will quantify the effects of 4R management (Right source, Right rate, Right time, and Right place) of nitrogen on nutrient (nitrogen, phosphorus, potassium, and sulfur) cycling in a corn-soybean system (Objective 1). This same approach will be used to determine the ability of cover crops to reduce nitrate losses (Objective 2) and maintain soil health (Objective 3) in a corn-soybean system, and the efficacy of organic cropping systems to reduce nitrate losses (Objective 2) and enhance soil health (Objective 3). We will determine how fall-planted cover crops and no-tillage within conventional and alternative corn-soybean rotations affect tile drainage water flow and nutrient concentrations, and how drainage water quality and soil profile water storage may differ in organic systems. We will use several indicators of soil health, such as aggregate stability and nitrogen mineralization potential, to compare and contrast conventional corn-soybean based cropping systems, corn-soybean based systems that include cover crops, and organic systems that include extended rotations. These comparisons are conducted using experimental plots with individual subsurface (tile) drains that allow robust measurements of hydrologic and nutrient balances. The research contributes to the Long Term Agroecosystem Research (LTAR) effort to ascertain the sustainability of and ecosystem services for conventional, i.e., business as usual (BAU), and aspirational (ASP) cropping systems, improving capabilities for acquiring, storing, and providing data to the LTAR Network and the larger agricultural community (Objective 4).
Progress Report
The Long-Term Agroecosystem Research (LTAR) Common experiment at the Kelley Farm Drainage Plots (KFDP) located near Ames, Iowa, was continued in 2021 and 2022. Established treatments contrasted different nitrogen (N) management strategies (Objective 1), and include measurements of nutrient losses (N, phosphorus (P), potassium (K), and sulfur (S) in tile drainage (Objective 2). The experiment compares a business as usual corn-soybean (C-S) cropping system with tillage and fixed N fertilizer applications to three alternative C-S systems: i) no-till C-S; ii) no-till C-S with a cereal rye winter cover crop; and iii) a system with a winter camelina crop following corn that is relay cropped with the subsequent soybean crop. Each of these alternative systems uses the late-spring nitrate test to determine spring sidedress N application rates. In 2021, camelina and soybean crops were harvested, and above-ground biomass and nutrient content measurements were made, as were nutrient contents for oilseed and grain. Similar research efforts are ongoing for the 2022 growing season. Established treatments at the Organic Water Quality research site located near Ames, Iowa, contrasted a conventional C-S agroecosystem with an organic corn-soybean-oat-alfalfa-alfalfa system and an organic forage production system (Objective 1), using replicated, tile-drained plots. In 2021, yield data were collected, but have yet to be summarized due to the retirement of the ARS Co-PI. Similarly, data on nitrate-N loss in tile drainage from these systems (Objective 2) during 2021 are still being processed. The use of a flame cultivator greatly reduced the weed density (visual assessment) in the 2020 corn crop and 2021 soybean crop. Key soil health metrics (Objective 3), including wet aggregate stability, organic carbon content, pH, extractable P and K, and potentially mineralizable N also were measured at both sites. Current data (2020 and 2021) from the KFDP were deposited in an internal database at National Laboratory for Agriculture and Environment. As available, these data are being exported to the NutriNet and LTAR databases (Objective 4).
Accomplishments
1. Cover crops and no-till show mixed results on nitrogen losses. Croplands with corn and soybean in the central United States are highly productive, but they pose a risk to the environment when nitrogen (N) is lost as nitrate in subsurface drainage or as nitrous oxide emissions. To meet increasing demand for environmentally sustainable farming, management practices must aim to reduce these impacts without sacrificing yield. ARS researchers in Ames, Iowa, assessed nitrate losses, nitrous oxide emissions, and crop production in systems using two conservation practices: planting cover crops (CCs) and using no-till management. Overall, neither tool consistently reduced both nitrate losses and nitrous oxide emissions. No-till management did not affect either one. CCs reduced nitrate losses but not nitrous oxide emissions. Rather, nitrous oxide emissions were linked with fertilizer N applications and weather patterns. Overall, the mechanisms regulating nitrate loss and nitrous oxide emissions did not appear linked. The study suggests it may be necessary to combine multiple conservation practices to reduce environmental impacts in these systems.
2. Cover crops that overwinter perform better in the upper Midwest. Over time, CCs may improve soil quality, and hence, crop production. CCs that not only provide soil cover but also produce significant plant biomass are of greater benefit. ARS researchers in Ames, Iowa, showed that in a tilled organic system, CCs grew best after an oat crop than after a corn or soybean main crop because of a longer period of growth and less competition for nutrients and water. CCs such as cereal rye and red clover that could survive the winter, produced more total biomass than turnips and hairy vetch that often did not survive well in the upper Midwest winters, suggesting that the latter may not be suitable for this region. The CCs had no effect on the main crop yields during this three-year study, but a longer study that included indicators of soil health would be useful. This information is important for scientists and crop advisors on the best CCs to use in the upper Midwest.
3. Streambanks contribute to phosphorus losses from agricultural lands. Losses of phosphorus (P) from agricultural lands represent a major cause of water quality impairment within Iowa and elsewhere. Producers and land managers have made progress over the last several decades in reducing soil-bound P losses from agricultural lands to receiving waters via soil erosion. However, there is a growing body of evidence that much of the sediment and P delivered to the surface waters from agricultural landscapes originates from streambanks. With a multi-step process, ARS researchers in Ames, Iowa, and collaborators estimated the contribution of streambank P sources to P export from the state of Iowa. Long-term, it was estimated that streambanks contribute approximately 31% of the annual P export from Iowa. Because of the magnitude of contribution, an improved understanding of streambank P contributions will help natural resource managers make improved recommendations for effective soil and water conservation practices that reduce P loading to rivers. This study may be among the first to address the issue of streambank P at a scale that has confounded many state and regional nutrient assessments.
4. Organic rotations provide more efficient water use in the spring and fall. More efficient use of plant-available water in the spring and fall may result from the plant biodiversity in organic systems compared with a conventional corn-soybean (C-S) system. If wet periods occur within the growing season, greater plant capture of water in the spring may reduce in-season surface runoff and leaching. ARS researchers in Ames, Iowa, and collaborators showed that an organic forage system took up more plant-available water in the spring and fall than a conventional C-S rotation. A four-year rotation (corn, soybean, oat with first-year alfalfa, second year alfalfa) was intermediate in water use. The leaf area index (a measurement of crop growth) did not show a consistent difference between conventional and organic corn or soybean. In the wet year of 2018, weed pressure hindered organic soybean growth. Data collected indicated that there was a good relationship between crop uptake of plant-available water and grain yield for both corn and soybean. Having crops on the land for a longer portion of the growing season could be beneficial in drying the soil during wet springs. Overall, this study demonstrated that organic agricultural systems have positive benefits for timing of water use. This information is important for organic farmers and their advisors.
Review Publications
Volf, M.R., Crusciol, C.A.C., De Azevedo, A.C., Thompson, M.L., Kovar, J.L., Rosolem, C.A. 2021. Potassium bioavailability in a tropical kaolinitic soil. Agronomy. 11(10). https://doi.org/10.3390/agronomy11102016.
Logsdon, S.D., Cambardella, C.A., O'Brien, P.L. 2021. Multispecies cover crops in organic agricultural systems in the upper U.S. Midwest. Agrosystems, Geosciences & Environment. 4(4). Article e20221. https://doi.org/10.1002/agg2.20221.
Logsdon, S.D., Cambardella, C.C., Delate, K. 2021. Organic agriculture effect on water use, tile flow, and crop yield. Agrosystems, Geosciences & Environment. 4(3). Article e20200. https://doi.org/10.1002/agg2.20200.
Schilling, K.E., Isenhart, T.M., Kovar, J.L. 2021. Contribution of streambanks to phosphorus export from Iowa. Journal of Soil and Water Conservation. 77(2):103-112. https://doi.org/10.2489/jswc.2022.00036.
