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United States Department of Agriculture

Agricultural Research Service


Location: Sustainable Agricultural Systems Laboratory

2009 Annual Report

1a. Objectives (from AD-416)
The long-term research objective of this project is to develop and translate fundamental agroecological knowledge into recommendations and products to improve the economic position of organic farmers and to improve their ability to meet consumer demand for organic products. Objective 1 is to develop component technologies and management strategies that lead to improved productivity, enhanced soil and water conservation, and efficient nutrient cycling on organic farms. Objective 2 is to understand agroecological principles that drive the function of organic cropping systems and quantify ecosystem services.

1b. Approach (from AD-416)
Approaches to developing component strategies include A) incorporating legumes into organic crop rotations to maximize nitrogen fixation, B) composting that provides a productive and safe amendment for organic agriculture, and C) optimal agronomic practices for managing nutrients and production on organic farms. Approaches to determining agroecological principles include investigating the following variables within the Beltsville long-term Farming Systems Project that compares two conventional and three organic rotations, A) crop performance, B) soil nitrogen dynamics in relation to nitrogen inputs, C) soil carbon sequestration and greenhouse gas flux, D) soil biological community structure in relation to soil quality and production performance, and E) soil erosion and nutrient loss potential.

3. Progress Report
Progress was made on component studies that make up Objective 1 and on all hypotheses related to the long-term Farming Systems Project that are part of Objective 2. For example, a component experiment was completed in fall of 2008 to determine the importance of planting date, tillage, and weed management on corn grown in a hairy vetch cover crop (Hypothesis 1.C1). Results of this experiment indicate that delayed planting did not improve weed management but that planting into a disked seedbed reduced weed biomass and increased post-planting cultivation efficiency compared to planting into a rolled vetch no-tillage seedbed. In addition, a postdoctoral associate was hired and has initiated field and laboratory research to address nitrogen availability in organic grain crops as outlined in Hypotheses 1.C1, 1.C2, and 2.B. We have also continued collecting and analyzing core data on the FSP including developing an algorithm based on short-term N2O flux patterns to interpolate N2O flux values for dates between actual sampling dates. We installed a wireless sensor network at FSP to collect near-continuous soil moisture and temperature data in collaboration with Johns Hopkins University scientists. We also continued on-farm research to develop best management practices for soil fertility under organic management practices and were awarded two OREI grants (> $3 million total) to conduct on-farm research to improve soil fertility and weed management on organic grain farms in the mid-Atlantic region.

4. Accomplishments
1. Role of weed competition in long-term organic corn production determined. Weeds can limit crop yield, particularly in organic systems where herbicide technologies are unavailable. Weedy and weed-free subplots were established within full plots of the long-term Farming Systems Project operated by ARS researchers at Beltsville, Maryland, to determine the effect of weed competition on corn yields during the first ten years of this experiment. Weed competition in organic systems reduced corn grain yield in all years, however annual variation was considerable with the highest rates of yield loss in three years with below average rainfall and the lowest rates of yield loss in three years with above average rainfall. Results showed that in above-average rainfall years, nitrogen availability was more limiting to organic corn yield than weed competition but in below-average rainfall years, weed competition was more limiting. These results will aid researchers and producers in focusing organic management practices depending on potential for drought at the field site.

2. Organic cropping systems mitigate global climate change. Agriculture can contribute to or mitigate global climate change. Researchers at ARS in Beltsville, Maryland estimated the global warming potential of no-till, chisel till and organic cropping systems at the long-term Beltsville Farming Systems Project. Global warming potential was greater in conventional no-tillage and chisel-tillage than in organic systems, primarily due to differences in soil carbon and secondarily to differences in energy use among systems. Despite relatively low crop yields in organic systems, the ratio of global warming potential per unit of crop yield was also significantly higher in conventional no-tillage and chisel-tillage than in organic systems. Results indicate that organic systems reduced global climate change, while conventional no-tillage and chisel-tillage systems contributed to global climate change. Practices common in organic systems, including incorporating legume cover crops and animal manures into soil, can help reduce global climate change compared to conventional systems, primarily by increasing the amount of carbon in the soil. These results will benefit policy makers, farmers, and others interested in reducing the impact of agriculture on global climate change.

3. Soil carbon pools are elevated four years after poultry litter is last applied. Application of animal manures to soils increases soil fertility and soil quality, however, there is little information on the duration of these effects after manure applications cease. Researchers at ARS in Beltsville, Maryland showed that the rate of decomposition of soil carbon was greater in cropping systems fertilized with poultry litter than in similar cropping systems fertilized with mineral fertilizers four years after poultry litter was last applied. The amount of carbon incorporated into the soil during the years that poultry litter was applied was positively related to the amount of soil carbon that decomposed at an intermediate rate four years after application. Since carbon decomposition rates are generally related to nitrogen decomposition rates, poultry litter applications likely had a positive residual effect on soil nitrogen fertility relative to mineral fertilizers four years after application. These residual effects of low rate applications of poultry litter should be considered when valuing poultry litter as soil amendments and as sources of fertility. These results will help farmers and researchers better account for impacts of manure applications on soil fertility and quality.

4. Carbon sequestration in organic grain cropping systems is not predicted by RUSLE2. Organic farmers are concerned that NRCS tools used to determine their soil conservation goals do not adequately predict soil carbon conservation in their soils. The assessment of soil carbon dynamics requires long-term experiments such as the long-term Farming Systems Project conducted by ARS researchers at Beltsville, Maryland, which is one of the few long-term experiments that compares diverse organic and conventional cropping systems. These researchers showed that soil carbon, to a depth of 1 m was greater in organic systems than in a conventional chisel till system. Soil carbon in organic systems was also as high as in a conventional no-till system. The NRCS tool, RUSLE2, predicted that soil C in these same organic systems would be substantially lower than in the no-till system and lower than in the chisel till system. Our results have served to help initiate conversations with NRCS to improve their evaluation of organic systems by better modeling practices such as incorporating cover crops and animal manures into soil.

5. Significant Activities that Support Special Target Populations
Members of this project’s research team participated in the planning, organization, and conduct of the “Farming for Profit and Stewardship Conference” that was held in Frederick, Maryland, January 16-17, 2009. This conference targeted small farms with female and organic producers in the mid-Atlantic area. Minority and disadvantaged farmers in Virginia and North Carolina were the target groups for a conference held at the Institute for Advanced Learning and Research in Danville, Virginia, November 5-6, 2009. An FSP member was instrumental in organizing and planning this conference, and is serving in a similar capacity for the fourth annual “Small Farm Family Conference” to be held November 9-10, 2009 in Richmond, Virginia. Members of this project’s research team were instrumental in organizing a workshop in Queen Anne’s County, Maryland, March 17, 2009.

Review Publications
Cavigelli, M.A., Dao, T.H. 2008. Residual impact of raw and composted poultry litter on soil carbon pools. Electronic Journal of Integrative Biosciences [serial online]. 6:30-40.

Cavigelli, M.A., Hima, B.L., Hanson, J.C., Teasdale, J.R., Lu, Y. 2009. Long-term economic performance of organic and conventional field crops in the mid-Atlantic region. Renewable Agriculture and Food System. 24:102-119.

Teasdale, J.R., Abdul Baki, A.A., Park, Y. 2008. Sweet corn production and efficiency of nitrogen use in high cover crop residue. Agronomy for Sustainable Development. 28:559-565.

Last Modified: 10/20/2017
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