2010 Annual Report
1a.Objectives (from AD-416)
Research proposed in this project includes both basic and applied research evaluating the impact of agricultural practices (tillage, residue management, soil fertility, and crop rotation) on soil productivity and crop yield and quality. Specific objectives include:.
1)Measure the effects of tillage, residue management, fertility, and crop rotation on physical, chemical, and biological properties of soils in agricultural crop production systems..
2)Develop crop rotation, nutrient, soil, residue, and pest management practices that improve farming efficiency (increase unit output/unit input), maintain or increase soil productivity, and improve crop yield and quality..
3)Measure the effects of corn stover/residue removed for biofuel feedstock on: (1) short-term balances of soil C and N; (2) crop yield and quality; and (3) soil resource condition.
1b.Approach (from AD-416)
Established long-term field experiments evaluating the effect of crop rotation, residue management, fertility and tillage will be utilized to evaluate the research hypothesis that crop rotations, crop diversity, and crop sequence improves soil quality and productivity and that increased crop diversity, attained through the introduction of alternative crops and improved crop sequences into the traditional corn/soybean rotation, will improve crop yield and quality while maintaining or improving soil quality. To address the hypothesis that no significant effect of genetic modification of corn genotype on soil microbes (DNA compositional measures) and their processes (e.g., C&N transformations) will be detectable, a field experiment will be established evaluating several different corn isolines with and with out genetically modified organisms. To evaluate the hypothesis that cover crops and integrated weed management strategies will increase biodiversity and enhance sustainable crop production, research will be conducted in two phases. Phase 1 will consist of a small-plot field experiment in which different species of grasses and legumes will be evaluated as cover crops in a corn/soybean/spring wheat rotation. The viability of cover crops as a management tool for weeds and insects relative to chemically-driven pest management will be investigated in Phase 2 of the research. Field and greenhouse experiments will be established evaluating a number of different soybean genotypes to test the hypothesis that soybean genotypes with significantly more root length and mass in the top 10 cm of soil (extensive fibrous root system) will have a more positive impact on soil organic matter, aggregate stability, and soil strength than other soybean genotypes.
We have completed a series of studies on the decomposition of Bt corn residue relative to non-Bt corn residue. This data has been analyzed and published. We found no differences in the decomposition of Bt and non-Bt corn residues, even when differential insect damage to the corn plants was evident.
We have analyzed data from a 3-year study evaluating nitrogen mineralization dynamics with and without cover crops in a corn-soybean-winter wheat rotation. We have found that the type of cover crop influences available nitrogen for the succeeding corn crop.
We have continued (for the fourth year) measuring greenhouse gas (CO2, CH4, N2O) fluxes on a biweekly basis in plots under alternative rotational management. This research is part of the nationwide ARS networks REAP and GRACEnet. We have continued (for the second year) measuring greenhouse gas (CO2, CH4, N2O) fluxes on a biweekly basis in plots under differing corn residue removal levels. This research is part of the nationwide ARS networks REAP and GRACEnet.
We have collected and begun analysis of data on the effect of corn residue removal on soil microbial communities using quantitative PCR of taxonomic groups. This research is part of the nationwide ARS network REAP.
We have initiated two studies that examine the effect of cover crops on mycorrhizal fungi and their provision of P to subsequent corn crops.
The impact of removing corn residue on soil quality is being evaluated to determine fine and course particulate organic matter. Initial results indicate that with greater amounts of residue removed from the soil surface, there is a decrease in fine particulate organic matter. This decrease in particulate organic matter could lead to a decrease in soil organic carbon as particulate organic matter is an indicator for short-term changes in soil carbon.
The impact of no-till soil management and complex crop rotation on soil quality and residue productivity was again measured in a long-term forage experiment established in 1995. Data from previous years has been analyzed, and a publication is being assembled. Experimental results will be of interest to local farmers, soil conservation districts, other scientists, and the Natural Resources Conservation Service.
The effects of grassland canopy management on species composition and soil carbon sequestration was again measured in a long-term CRP grassland experiment established in 2000. Data from previous years have been published, and technology transfer has taken place.
Grassland management for increased biomass production and soil carbon (C) storage. Because there are 13.5 million Conservation Reserve Program acres in the north central US, a region that is also slated to provide cellulosic feedstocks for biofuels, scientific studies on management options for native grass mixtures planted into previously-cultivated cropland and the effects these management options have on grass biomass production and soil carbon sequestration are important priorities. ARS scientists at Brookings South Dakota, in collaboration with scientists at South Dakota State University, are conducting field research which revealed that methods used to manage grass canopies had significant effect upon the rates of biomass production and soil C accumulation during the first 9 years of the long term experiment. Thus, the choice of grassland management methods when converting cropland to grassland should be based upon consideration of grass biomass utilization as well as soil C accumulation. If the goal was to use harvested grass biomass as a feedstock, an annual late-summer haying treatment could be recommended with the understanding that this would be slightly less efficient at increasing the soil C accumulation rate. A spring burn treatment would be recommended if the goals were to restore or maintain dominance of warm season grasses in mixed grasslands while only slowly increasing soil C accumulation, while no canopy management would be recommended if the primary goal was to increase soil C accumulation. This customer-driven research provides biomass and soil data that will aid farmer decisions related to the type of grassland management strategies that best fit their current and future agronomic needs.
Management strategies to increase crop tolerance to soybean aphids. Understanding how soybean aphids, the most damaging soybean insect in the north-central United States, affect soybean crop growth may suggest new crop and soil management methods that increase crop tolerance to this pest. ARS scientists at Brookings South Dakota, in collaboration with scientists at South Dakota State University, conducted controlled environment studies to investigate soybean aphid feeding effects on nitrogen metabolism (e.g. root nodule characteristics, nitrogen fixation, and levels of nitrate and ureide nitrogen) and plant growth. Aphid-induced reductions in nitrogen fixation, coupled with decreased dry weight accumulation, caused shoot concentration of fixed nitrogen compounds (e.g. ureides) to remain unchanged in aphid-injured plant when compared to uninfested plants. In contrast, accumulation of soil-available nitrogen compounds (nitrates) was greater in aphid-damaged shoot tissue suggesting nitrate-N accumulation was less sensitive to aphid injury than dry weight accumulation. These findings demonstrate the importance of soil nitrogen in mediating crop responses to soybean aphids. Additional research on the use of crop and soil management strategies that manipulate soil nitrogen availability as a way to increase crop tolerance to soybean aphids is therefore warranted.
Nitrogen reduces yield loss to cereal aphids and aphid-vectored disease. Potential reductions in root system function in aphid-infested or barley yellow dwarf virus-infected oat plants may play an important role in causing grain yield reduction. ARS scientists at Brooking, South Dakota and Morris, Minnesota studied how cereal aphids (bird cherry oat aphid, greenbug, Russian wheat aphid) and aphid-transmitted plant disease (barley yellow dwarf virus) influenced mineral nutrient densities of oat leaves, kernels, and groats under field conditions. Nitrogen nutrients, in terms of nitrogen use efficiency, nitrogen harvest index, and carbon:nitrogen ratio, were important in mediating positive cereal plant responses to stress caused by aphid feeding damage or aphid-vectored disease. This information is valuable to small grain producers because it demonstrates that farmers who undertake crop and soil management strategies that guard against crop nitrogen deficiency will receive additional benefits of increased insect and disease tolerance.
No evidence found that Bt corn residues decompose more slowly than Non-Bt residues. Since Bt corn was introduced, there have been informal and formal communications circulating in the agricultural community that Bt corn residues were more resistant to decomposition than non-Bt corn residues. ARS scientists at Brookings, South Dakota, have completed a series of studies published in three papers that found no evidence that the decomposition of corn residues was linked to the presence of the Bt gene in the corn hybrid. These studies examined multiple corn hybrids from a single manufacturer, hybrids from different seed manufacturers, and hybrids grown under conditions of differential insect pressure. With the rapid expansion of genetically-modified crops, controlled studies evaluating the potential for unintended effects due to genetic modification provide a firm basis for evaluating the advantages and disadvantages of this technology.
Lehman, R.M., Osborne, S.L., Prischmann-Voldseth, D., Rosentrater, K.A. 2010. Insect-Damaged Corn Stalks Decompose at Rates Similar to Bt-Protected, Non-Damaged Corn Stalks. Plant and Soil Journal. 333:481-490. DOI 10.1007/s11104-010-0364-8.
Jaradat, A.A., Riedell, W.E. 2010. Nutrient Densities, Carbon:Nitrogen Ratios, and Midday Differential Canopy Temperature Impact Grain Yield of Stressed Oat. Journal of Plant Nutrition. 33(10):1531-1554.
Riedell, W.E., Catangui, M.A., Beckendorf, E.A. 2009. Nitrogen Fixation, Ureide, and Nitrate Accumulation Responses to Soybean Aphid Injury in Glycine max. Journal of Plant Nutrition. 32:1674-1686.
Riedell, W.E., Osborne, S.L., Schumacher, T.E., Pikul Jr, J.L. 2010. Grassland Canopy Management and Native Tallgrass Species Composition Effects on C and N in Grass Canopies and Soil. Plant and Soil Journal. DOI 10.1007/s11104-010-0341-2.