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United States Department of Agriculture

Agricultural Research Service

2007 Annual Report

1a.Objectives (from AD-416)
Enhance carbon sequestration for improved soil quality and erosion control; Quantify the form and release of major nutrients as affected by soil redox potential; Determine the impacts of conservation tillage on fate of pesticide in soil.

1b.Approach (from AD-416)
Quantify dissolved organic carbon in runoff samples from subwatersheds in the St. Joseph River; Identify enzymes as soil quality indicators; Monitor effects of changing soil redox potential on nutrient form and release; Quantify the fate of atrazine, metolachlor and glyphosate under varying temperature and crop residue; Quantify the competition between glyphosate and phosphorus and glyphosate and potassium for possible nutrient decline due to glyphosate usage.

Soil microbiological activity and aggregation in Oxisols. Mechanized agriculture is increasing rapidly in the Cerrado region of Brazil. Many Amazon River tributaries flow through this area, and increased production could lead to increased sedimentation of the river ecosystems. ARS and Brazilian scientists undertook an experiment to determine the impact of two decades of agricultural production on soil quality on an Oxisol that was typical of soils covering 46% of the Cerrado. Similar soils are found in the US in Hawaii, Puerto Rico, Guam, American Samoa, and the Northern Mariana Islands. We looked at three tillage regimes that were similar to those used in the US Corn Belt. We found that soil biological activity as measured through soil enzyme activities and carbon and nitrogen mineralization, to be greater in no-till than in the other managed systems, which is similar to trends seen in the more-studied temperate soils. Soil enzymatic activity was highly correlated with nitrogen and only weakly related to soil organic carbon, differing from temperate soils, which generally show a high correlation between enzyme activity and soil carbon. Iron and aluminum are considered to be the dominating soil aggregating agent in Oxisols, however our results showed that soil organic matter also played an important role in the stability of aggregates in tropical soils, with tillage and subsequent loss in organic matter resulting in decreased aggregation. This work impacts current theories of aggregation by showing the importance of soil carbon in aggregation in Oxisols. Also, contrary to results from temperate soils, soil enzyme activity is more correlated to soil nitrogen rather than carbon. This accomplishment supports NP 202 Soil Resource Management Action Plan, Problem Area #3: Soil carbon, Focus Area #1: Measurement tools for soil carbon, and #3: Management effects on soil carbon; and Problem Area #1: Understanding and managing soil biology and rhizosphere ecology, Focus Area #1: Improved understanding of soil biology and rhizosphere ecology.

Use of gypsum amendments on reducing nutrient loss from soil. Loss of N and P from soil to water is not only an agronomic but also an environmental and human health problem. The main objective of this study was to evaluate the effect of gypsum amendment and soil-exchangeable Ca and Mg on the concentration and loss of nutrients in runoff, sediment, and soil. The experiment was performed in the laboratory using a programmable rainfall simulator and erosion pans. The soil was a Miami silt loam, and treatments included a gypsum amendment, five target exchangeable Ca/Mg ratios, and a control. Nitrogen, P, and K were applied in all treatments based on soil test results and standard recommendations for corn. The fertilizers were mixed with the soil to a 2.5-cm depth before pre-wetting. Gypsum was applied to the surface just before the rain. Two rainfall intensities (30 and 60 mm h-1) were simulated, and infiltrated water and runoff samples were taken every 5 min over 2 h. Nitrate-N, ammonium-N, and P in runoff, sediment, and soil were determined. The results showed that gypsum, as compared with the control, significantly decreased the total loss in runoff of dissolved reactive P, total P, soluble ammonium-N, and total N by 85, 60, 80, and 59%, respectively. The concentration of these constituents was also significantly decreased by 83, 52, 79, and 50%, respectively. Nitrate-N concentration in runoff was not decreased by gypsum. Gypsum also affected sediment and soil water-extractable P. The only significant effect of exchangeable Ca/Mg ratios was observed in the sediment water-extractable P, where Ca-treated soil decreased by 50% the concentration of P compared with Mg-treated soil. The impact of this study will be a new management strategy to decrease the transport of total N and total P in runoff and the importance of Ca in the soil solution to decrease P solubility. The accomplishment supports NP 202 Soil Resource Management Action Plan, Problem Area #4: Nutrient management for crop production and environmental protection; Focus Area #2: Management practices and strategies for increasing nutrient use efficiency.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of non-peer reviewed presentations and proceedings5
Number of newspaper articles and other presentations for non-science audiences1

Review Publications
Favaretto, N., Norton, L.D., Joern, B.C., Brouder, S.M. 2006. Gypsum amendment and exchangeable calcium and magnesium affecting phosphorus and nitrogen in runoff. Soil Science Society of America Journal. 70(5)1788-1796.

Hanson, J.D., Liebig, M.A., Merrill, S.D., Tanaka, D.L., Krupinsky, J.M., Stott, D.E. 2007. Dynamic cropping systems: increasing adaptability amid an uncertain future. Agronomy Journal 99:939-943.

Green, V.S., Stott, D.E., Cruz, J.C., Curi, N. 2007. Tillage impacts on soil biological activity and aggregate stability in Brazilian Cerrado Oxisols. International Journal of Soil and Tillage Research. 92:114-121.

Last Modified: 12/1/2015
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