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United States Department of Agriculture

Agricultural Research Service

2010 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; and 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; and 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.

3.Progress Report
The last two ARS Experimental Watersheds were sampled for soil sequestration and soil quality (Cheney Lake, (KS); Upper Snake River, (ID)). Original plans were for 12 watersheds, but to date sixteen have been sampled. Analysis has been going slower than anticipated, however analysis has been completed for the first nine watersheds (South Fork (IA), Walnut Creek (IA), Leon River (TX), Little River (GA) and Ft. Cobb (OK), Cedar Creek (IN), Beasley Lake (MS), Choptank (MD), and Durham (NH)). One paper has been submitted, several others are being prepared.

The Soil Management Assessment Framework (SMAF) has been updated to include a new indicator: soil ß-glucosidase activity. The paper on the development of the ß-glucosidase indicator scoring curves has been published. ß-glucosidase is involved in the decomposition of plant residues and roots.

Monitoring of trace gas emissions and carbon sequestration continues at two experimental sites: ACRE, west of West Lafayette, a Mollisol soil and TPAC, south of Lafayette, an Alfisol soil. Both sites include corn-soybean rotations (five treatments) and ACRE includes grass management plots. This is the end of the third year of this experimental phase; one more year of data is needed for publishable material.

Monitoring of changes to soil quality characteristics, carbon sequestration and productivity are continuing in the field experiment designed to determine impacts of corn residue removal on the soil.

A series of incubation experiments are underway to study to explore the impact of glyphosate application rates on the form and release of soil P and K as well as impact on microbial activity.

A set of experiments is underway in the field and in the laboratory to study the impact of redox potential on nutrient cycling – this is in regard to the frequent periods of soil saturation followed by drainage. Up until now, little attention has been paid to the impact of this cycling system.

1. Soil quality assessment on a watershed scale. Soil quality assessment is a proactive process for understanding the long-term effects of soil and crop management practices within agricultural watersheds. In the South Fork of the Iowa River Watershed, an aerial survey was conducted during the summer of 2006 to identify areas with both well-developed and poor canopy growth in fields that were planted to corn (Zea mays L.). Our objective was to determine if a soil quality assessment could identify reasons for the poor canopy development. Soil bulk density (BD), aggregate stability, texture, water-filled pore space (WFPS), pH, electrical conductivity (EC), soil organic C (SOC), total N, extractable nutrients and trace elements, microbial biomass C (MBC), potentially mineralizable C (Cmin) and N (Nmin), and ß- glucosidase (BG) activity were quantified. We used the Soil Management Assessment Framework (SMAF) tool to assess and interpret soil quality indicator variables both individually and as an integrative index. When the data were separated by areas of normal or poor corn canopy development, mean indicator values were slightly lower in poor canopy areas. Using SMAF indicator scores, BD, WFPS, EC, SOC and MBC were significantly lower in the areas with poor canopy development; however, no single indicator scored significantly less across all fifty fields. When separated by landscape position (hilltop, sideslope, toeslope or depression) or by previous crop (corn or soybean (Glycine max (L.) Merr)), almost all the indicator scores were significantly different in the normal vs. poor canopy areas. A majority of fields had multiple indicators that scored at least 0.10 lower in the poor canopy area than the corresponding normal canopy areas. Soil quality assessment on a field by field basis thus provides an approach for identifying potential specific soil-based causes for the poor canopy development.

2. Herbicides affect nutrient cycling. Farmers have observed symptoms of nutrient deficiency in crops where the herbicide glyphosate has been used for several years in a row. We found that one reason for this is that long term exposure to glyphosate affects soil enzyme activities pivotal in nutrient cycling. These findings will impact weed management decision making with soil quality and crop yield in mind.

Review Publications
Stott, D.E., Andrews, S.S., Liebig, M.A., Wienhold, B.J., Karlen, D.L. 2009. Evaluation of ß-Glucosidase Activity as a Soil Quality Indicator for the Soil Management Assessment Framework (SMAF). Soil Science Society of America Journal. 74(1):107-119.

Wienhold, B.J., Karlen, D.L., Andrews, S.S., Stott, D.E. 2009. Protocol for indicator scoring in the soil management assessment framework (SMAF). Renewable Agriculture and Food System. 24(4):260-266.

Last Modified: 11/28/2015
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