Location: Agroecosystems Management Research2011 Annual Report
1a. Objectives (from AD-416)
Overall objective: To develop and transfer technologies to manage Midwestern cropping systems which enhance soil and water quality and maintain profitability. Objective 1: Develop strategies for incorporating annual and perennial cover crops into continuous corn and corn-soybean management systems. Objective 2: Quantify changes in C and N cycling resulting from inclusion of cover crops within corn-soybean based cropping systems. Objective 3: Assess erosion and soil quality impacts and production risk associated with using cover crops, complex rotations, and bioenergy production in Midwestern cropping systems.
1b. Approach (from AD-416)
A combination of controlled environment, plot, and watershed-scale studies will quantify functional components of cover crops to develop enhanced Midwestern cropping systems. Up to fifteen winter rye, triticale, and wheat cultivars will be obtained from commercial sources and planted with a grain drill following soybean harvest. Results will quantify corn grain yield response to cultivars of winter rye, wheat, and triticale used as winter cover crops in a corn-soybean rotation. Perennial cover crop research using various herbicide and strip tillage management systems in continuous corn with stover removal will quantify C inputs from cover crops and their effect on corn yield. Inter-species differences in plant growth parameters may affect a cover crop’s potential to sequester soil C. Research will quantify total aboveground and belowground C and N allocation, rhizosphere respiration, and net mineralized N for selected cover crops grown under controlled conditions, quantify changes in surface residue, root, and soil C and N pools and cumulative net mineralized N and respired C during decomposition of cover crop biomass under controlled conditions, and field experiments to quantify the effects of the cover crop on soil C cycling and storage within extended corn-soybean based crop rotations with and without compost amendment. Field studies will evaluate the impact of corn stover removal with and without rye and perennial cover crops on soil quality. A modeling study will evaluate the effect of a winter rye cover crop on soil erosion in corn-soybean rotations using georeferenced terrain and cropping system data from two western Iowa watersheds. Evaluation of risk to crop yield induced by the removal of soil water by cover crops will be assessed with a combination of simulation models and experimental observations. Simulation results will be obtained with the Precision Agricultural-Landscape Modeling System (PALMS) model. The simulation model allows for an extension of the results to different soil types and climates and will be used to assess the degree of risk imposed on the main crop through soil water removal patterns.
3. Progress Report
Data collection has been completed and analysis of data is continuing for hypothesis 1.1. Results so far indicate that response of corn growth to cover crop genotypes is not consistent from year to year and a different approach is needed. Planning for new experiments is beginning and may be implemented beginning this fall. The third year of data has been analyzed for hypothesis 1.2 and the results are encouraging. Corn growing in a Kentucky bluegrass living mulch with paraquat and glyphosate herbicide suppression and fall strip-till yielded similarly to the no living mulch control in all three years. Additional research is being planned to scale-up the research and also consider modeling efforts to predict the response of this cropping system in varying climactic environments. This year’s near surface samples have been collected for soil carbon, particulate organic matter, and potential nitrogen nitrogen mineralization and are being processed for hypothesis 1.3. A field study started in the fall of 2010 using annual medics in different proportions with oat to identify carbon and nitrogen partitioning of the cover crops and quantify how much nitrogen the cover crops provide to the subsequent corn crop (hypothesis 2). Analysis of samples from last year is nearing completion for hypothesis 3.1. A rye winter cover crop was planted in a corn silage-soybean rotation and soil carbon, potential nitrogen mineralization, and particulate organic matter were measured in the upper 10 cm of soil. Sample processing and measurement are continuing, but early data show greater levels of potential nitrogen mineralization and particulate organic matter when rye cover crops are grown with corn silage than corn silage without a rye cover crop. This indicates that a winter rye cover crop can help to maintain soil quality in rotations where corn shoot biomass is removed. Work on hypothesis 3.3 is continuing with data set assembly and model runs planned for summer and fall 2011. Established sulfur fertilizer plots (fourth year) on a Clarion loam soil to evaluate the performance characteristics of three sulfur sources (13-33-0-15S, 21-0-0-24S, and 12-0-0-26S) for corn, and summarized four years of data. At the organic farming water quality site in central Iowa, benchmarks were placed and 30 experimental plots were established. Tile drains, sumps, and water flow barriers were installed in each of the 30 plots. The installation was the first of two required installations prior to implementation of the cropping systems. The second requirement is the installation of electrical power to the site, which will be completed in August 2011.
1. Sustainable bioenergy cropping systems. Corn stover (biomass remaining after harvest) removal for production of ethanol will likely reduce soil organic matter and soil fertility. These effects of corn stover removal may be mitigated by using a living mulch to offset carbon exports, control soil erosion, and enhance nutrient cycling. Living mulches are plants grown concurrently with the corn crop and they can compete with the main crop for resources, particularly water. An Agricultural Research Service (ARS) scientist in Ames, Iowa, quantified competition between living mulches and corn compared to corn growing alone in cropping systems where greater than 95% of the corn stover is harvested as a bioenergy feedstock. Two of the three growing seasons had above normal rainfall and the living mulches and corn in no-till had increased soil water content, but lowered grain yield compared to corn alone. Corn grain yields were not different in a Kentucky bluegrass and corn strip-till treatment compared to corn alone all three years. These results are important because the most viable corn living mulch cropping system with stover removal can likely offset 25 to 30 percent of the carbon harvested in the stover and provide greater than 85 percent soil cover, thereby preserving soil productivity. Producers interested in adopting living mulch cropping systems can consistently produce high corn grain yields and maximize stover harvest by using a living mulch with corn.
2. Is sulfur limiting corn grown on eroded Midwestern U.S. soils? Sulfur is an essential plant nutrient that must be available to corn roots in order to achieve optimum growth of the plant. Our understanding of the effects of removing both corn grain and stover as potential bio-energy feedstock on soil sulfur supplies is limited. Agricultural Research Service (ARS) researchers in Ames, Iowa, evaluated the performance of several sulfur fertilizers for corn grown in Iowa. After three years, it was found that an application of 30 pounds of sulfur per acre increased early-season growth and plant sulfur concentrations compared with untreated areas. It was also found that sulfur fertilizer increased grain yield by up to 12 bushel per acre. The agronomic efficiency of sulfur was greatest for the 13-33-0-15S material in 2006 and 2008, but there was little difference among sources in 2007 and 2009. In addition, significant soil variability at the research sites probably limited crop response to sulfur. For several reasons, including erosion of high-fertility hill slope soils, fewer sulfur impurities in fertilizers, and decreased atmospheric deposition of sulfur throughout the upper Midwest, our results suggest that sulfur may quickly become a limiting nutrient for corn grown to supply bio-energy feedstock. The results of this research benefits both commercial growers and the fertilizer and ethanol industries by providing nutrient management guidelines that maximize crop utilization and biomass yields.
3. Can cover crops be managed to self-seed? Perpetuating winter small grain cover crops through self-seeding may increase their adoption by reducing the risk of cover crop establishment in the fall and lowering the cost. An Agricultural Research Service (ARS) scientist in Ames, Iowa, used winter rye, wheat, and triticale to develop self-seeding cover crop systems in a soybean-corn rotation. The study revealed that plant establishment through self-seeding was more consistent using a wheat cover crop and mechanical seed dispersal before soybean harvest. The combination of these two factors consistently increased green groundcover, regardless of the initial cover crop seeding rate. The significance of this research, in addition to lowering the cost and risk of establishing cover crops, is to extend the ecological functions that cover crops perform beyond their normal termination dates. Although some competition may occur between the cover crop and main crop growing concurrently in conventional crop production systems, producers using organic crop production techniques could adopt these systems because of the potential for enhanced weed suppression without soil disturbance.
Singer, J.W., Heitman, J.L., Hernandez Ramirez, G., Sauer, T.J., Prueger, J.H., Hatfield, J.L. 2010. Contrasting methods for estimating evapotranspiration in soybean. Agricultural Water Management. 98(1):157-163.