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:
During the five year life of this project, researchers working at the long-term Farming Systems Project (FSP) found that increasing crop rotation length and complexity reduce production and other challenges in organic systems. Corn yield was 10 and 30% greater in a crop rotation that included a perennial forage crop compared to shorter rotations that included only annual crops. Increasing crop rotation length and complexity also reduced predicted soil erosion, soil nitrous oxide (N2O) emissions, economic risk, animal manure inputs and soil phosphorus loading. Additional progress in the past year is described below. Field experiments to evaluate OMRI-approved fertilizers in organic forage production are in their fourth year (sub-obj. 1.A). Test mixtures containing dairy manure solids, old hay and animal bedding, and vegetative food waste were composted using a mechanically aerated in-vessel composting system, and procedures for evaluating gaseous emissions were developed, tested, and installed (sub-obj. 1.B). The second year of field studies comparing survival of generic and non-pathogenic strains of Escherichia coli in organically and conventionally managed fields were conducted using various amendments (sub-obj. 1.B). We performed experiments to evaluate the impact of cover crop mixes (rye, hairy vetch) and manure sub-surface banding on soil N2O emissions (sub-obj. 1.C). The lead scientist collaborated with scientists from the University of Maryland to compare N2O emissions from organically-managed vegetable crops grown using four different cover crop management practices (sub-obj. 1.C). We monitored population and community dynamics and weed-crop competition for a fourth year in permanent weed-free and weedy check plots in organic and conventional systems in the FSP (sub-obj. 2.A). Manuscripts were initiated describing research that evaluated the influence of long-term soil management on weed-crop competition relationships (sub-obj. 2.A). We compiled 14 years of data to compare nutrient budgets (N, P, K, C) and evaluate nutrient management, and to compare carbon budgets and evaluate soil carbon sequestration and potential sequestration mechanisms among cropping systems at the FSP (sub-obj. 2.B, sub-obj. 2.C). We characterized soil carbon fractions collected from diverse FSP systems using near-infrared, mid-infrared and pyrolysis spectra as part of our effort to evaluate mechanisms of soil carbon sequestration (sub-obj. 2.C). A scientist from Brazil (EMBRAPA), in association with colleagues at the University of New Hampshire, compared output from the DNDC model with two years of soil N2O emissions data to evaluate model predictions among FSP cropping systems (sub-obj. 2.C). A visiting PhD student from Brazil and a high school intern measured soil N2O emissions following application of conventional and newly-designed slow-release nitrogen fertilizers (sub-obj. 2.C). A multi-location project was initiated by NP216 project scientists to determine indirect and legacy effects of glyphosate application on soil resident microbes associated with corn and soybean roots and implications for general plant health (sub-obj. 2.D).
1. Reducing soil greenhouse gas emissions will require novel agricultural approaches. Agricultural soils are the dominant source of nitrous oxide (N2O), a greenhouse gas and catalyst of stratospheric ozone decline. U.S. emissions continue to increase despite substantial increases in crop and animal productivity and associated reductions in N2O emissions per unit of production. Reducing emissions of N2O requires novel approaches because of the complex, mostly biological, processes responsible for its production. ARS scientists from the Sustainable Agricultural Systems Laboratory, Beltsville, MD and other areas along with university and industry colleagues summarized trends and challenges of reducing N2O emissions for the National Climate Assessment (NCA), coordinated by the President’s Office of Science and Technology Policy. A modeling analysis in the NCA completed in cooperation with ARS scientists from Fort Collins, CO, showed that N2O emissions can be substantially reduced by decreasing consumption of animal protein in developed countries and intensifying agriculture in developing countries. These results are of interest to policymakers who rely on scientific data to make decisions.
2. Organic cropping systems provide ecosystems services that rival no-till cropping systems. Organic farming ecosystem services have not been compared to those of conventional no-tillage farming in the past. ARS scientists in the Sustainable Agricultural Systems Laboratory at Beltsville, MD, using data from the long-term Farming Systems Project, found that soil carbon storage and nitrogen fertility can be greater, while impact on climate change can be lower in organic systems using animal manures and cover crops compared to conventional no-tillage systems using conventional fertilizer and cover crops. Ecosystem services of organic systems are improved by expanding crop rotations to include greater crop diversity, using integrated nutrient management, and reducing tillage intensity and frequency. However, soil erosion and labor requirements are greater and crop yields, on average, are lower in organic than no-tillage systems. This research quantifies how organic farming practices can improve provision of ecosystem services and also how organic farming can be improved, and is of interest to organic farmers, farmers considering transitioning to organic, and policymakers and others interested in augmenting ecosystem services provided by all farming systems.
3. Genetic control of hairy vetch flowering time decoded. In no-till organic cropping systems the onset of flowering indicates the earliest time a farmer can mechanically terminate cover crops without the use of herbicides or tillage. Developing earlier-flowering cover crops should increase adoption of these conservation cropping systems since the late planting dates necessitated by late flowering cover crops can be a disincentive to adoption. ARS scientists from the Sustainable Agricultural Systems Laboratory, Beltsville, MD identified genetic traits associated with significant variation in flowering time among accessions in the USDA hairy vetch germplasm collection. Five key flowering genes associated with initiation or inhibition of flowering were identified among the hairy vetch genotypes. These genes are regulated during transition from vegetative to flowering growth stages. Information on differences in the regulation of these genes could be used to rapidly identify hairy vetch varieties in future breeding programs with flowering times better synchronized with agronomic needs. This information is useful to crop breeders and other scientists interested in improving the value of hairy vetch as a cover crop.
4. Some types of biochar may increase N losses from soil. Biochar is a carbon rich byproduct from pyrolysis of plant biomass that can increase soil productivity and can be used for long-term storage of carbon in soils. Limited information is available on how biochar influences different nitrogen pools in the soil and nitrogen availability to crops. ARS scientists from the Sustainable Agricultural Systems Laboratory, Beltsville, MD in collaboration with University of Georgia cooperators found that biochar made from pecan shells, peanut hulls, and poultry litter increased losses of nitrogen from soils. Losses were the result of ammonium volatilization caused by biochar-induced increases in pH. Little evidence of increased inorganic nitrogen retention or mineralizable N fractions was observed when these biochars were added to soil. Responses varied among biochars, indicating the need for caution in use of biochar in agricultural soils. Biochar chemical and physical characterization could help aid in matching biochar to soil type as well as identifying appropriate land use. These results will be of interest to farmers, agricultural professionals and others considering using, or advising on the use of, biochar.
5. Managing soil biodiversity and ecosystem services. Ecosystem services are those provided by natural systems, such as providing clean drinking water, regulating climate, crop pollination, and recycling of decomposing materials. Many ecosystem services are carried out by soil organisms. The impact of the diversity of soil organisms on provision of ecosystem services has not been well summarized. ARS scientists from the Sustainable Agricultural Systems Laboratory, Beltsville, MD and a University of Maryland colleague synthesized the latest information regarding managing soil biodiversity and the impact on attendant ecosystem services in a book chapter. Agricultural management impacts on ecosystem services and soil biodiversity were often complex. Management responses may be subtle and vary with soil type, climate, ecosystem, type of organism and ecosystem service. Nonetheless, management that improves ecosystem services is also likely to improve soil biodiversity. This information will be of interest to the international agricultural research community that is increasingly recognizing the crucial roles ecosystem services play in intensive agricultural production systems.
6. Composting at high temperatures kills disease organisms of cacao. Cacao pod husks, which are typically left in the field after cacao beans are harvested, represent a major disposal problem for the cacao industry and can serve as a significant reservoir of disease inoculum. Composting and anaerobic digestion were investigated as potential disinfection technologies and as a means of producing an organic fertilizer for cacao farmers. In laboratory experiments ARS scientists from the Sustainable Agricultural Systems Laboratory, Beltsville, MD, found that disease organisms that survived when composted using standard techniques did not survive under thermophilic composting conditions, even for short periods. Fifteen hour exposure in a 35C mesophilic anaerobic digestor will disinfect cocoa pod husks of Phytophthora, thereby rendering the compost or digestate suitable for horticultural uses as an organic fertilizer. These results will be of interest to the cocoa industry.
7. Solarization and biofumigation reduce survival of harmful bacteria on spinach leaf residue incorporated into soil. Contamination of spinach and raw vegetables by E. coli and Salmonella has resulted in hundreds of cases of gastroenteritis, numerous cases of kidney failure, and even fatalities. The leafy greens industry has incurred millions of dollars of economic losses from reduced sales and from compensation settlements to victims of foodborne illnesses. Preventing contamination of fresh produce is an important crop protection strategy. Animal manure used as fertilizer or left by wildlife can contribute bacterial contaminants. High tunnel production provides some environmental protection for high value crop production, but cannot exclude all wildlife. This study showed that covering soil with a clear plastic film (solarization) and using biofumigation techniques (cabbage leaf incorporation into soil, 20 percent vinegar drench, or a commercially-available, organically-approved plant disease control soil drench) significantly reduced E. coli survival over a two week period. Non-treated soil and the white and black plastic reduced E. coli populations, but not as dramatically as the clear plastic film. These results are important because they show that soil solarization combined with natural product biofumigants provide an effective strategy to reduce E. coli contamination in high value produce cropping soils in a short time. These results will be of interest to organic and conventional leafy greens producers and the leafy greens processors and marketers.
Spargo, J.T., Cavigelli, M.A., Alley, M.M., Maul, J.E., Buyer, J.S., Sequeira, C.H., Follett, R.F. 2012. Changes in soil organic carbon and nitrogen fractions with duration of no-tillage management. Soil Science Society of America Journal. 76(5):1624-1633.