Location: Soil, Water & Air Resources Research2012 Annual Report
1a. Objectives (from AD-416):
1) Quantify the effects of soil management practices and amendments, including humic substances, to enhance soil organic matter and carbon and nitrogen dynamics for improving soil productivity. 2) Measure the impact of soil management practices that will increase soil aggregation, reduce compaction, affect crusting, and minimize trace gas exchange processes within Midwestern soils for enhanced soil productivity and environmental quality. 3) Develop sustainable biofuel feedstock production systems using soil quality assessment tools to ensure the practices sustain productivity and protect soil, water and air resources.
1b. Approach (from AD-416):
Biochemical analyses will be used to distinguish between labile and recalcitrant fractions of soil organic matter to improve the knowledge base regarding the effects of residue management on short-term soil processes (nutrient cycling, soil structure, and crust formation) and long-term carbon sequestration. This basic knowledge will then be applied to current production problems associated with providing sustainable supplies of bioenergy feedstock and enhancing grain yields to help meet ever-increasing food and feed demands. Utilizing corn, soybean, and small grain (i.e. rice, rye, and wheat) cropping systems, soil management practices to increase corn growth and grain yield will be evaluated in multiple field experiments. Various single-pass corn stover harvest and crop management strategies, cover crops, crop rotations, and tillage intensity will provide the crop production systems within which soil quality will be measured and the chemical nature and cycling of soil organic matter fractions will be quantified using seasonal analyses of amino acids, amino sugars, carbohydrates, phenols, and fatty acids. Effects of soil aeration on the decomposition of crop residues and the subsequent quality of soil organic matter, efficiency of nitrogen (N) cycling, and crop grain yield will be quantified in these experiments. The soil biochemical measurements coupled with soil physical process measurements will be used to augment the knowledge base related to soil quality assessment at plot scales for potential extension to field scale assessments. Project results will quantify the effects of crop residue management on soil physical and biochemical properties contributing to economic yields and long-term sustainability of major cereal cropping systems, leading to improved soil management practices.
3. Progress Report:
Progress on this project focused on four of the hypotheses and discoveries within Objective 1, determination of the effects of management practices and amendments on soil organic matter dynamics and their role in soil productivity, and Objective 3, development of sustainable biofuel feedstock production systems. We gained substantial understanding of the effects of corn residue management on soil organic matter fractions (Hypothesis 1.1). Several physical and chemical fractions were extracted from two soil depths of biofuel treatments that differed in their rate of corn residue return. The masses of two young physical fractions in the upper soil depth increased with increasing crop residue return, but the mass of a young chemical humic fraction was maximized in both depths with an intermediate rate of residue return, as were total soil stocks of nitrogen and organic carbon. To determine whether the chemical natures of the fractions were affected by residue return, we began their analysis for light absorption and carbohydrates content. Toward milestones that were belatedly added to Hypothesis 1.1, the benefit of a humic product to corn growth was demonstrated in most of 30 farmers’ fields for a third year. Under Hypothesis 1.2, the benefits of timely soil aeration to maintained soil nitrogen availability and rice crop yields while reducing water inputs were demonstrated in Arkansas. We continued regular progress toward development of sustainable biofuel feedstock production systems (Objective 3). Field studies focused on developing guidelines for sustainable corn stover harvest for bioenergy or other bioproducts (Hypothesis 3.1) were continued at five locations in Iowa. All are contributing to the multi-location Renewable Energy Assessment Project (REAP). At one location, use of white clover as a perennial cover crop was discontinued because the clover could not survive under the low light conditions created by corn grown at populations greater than 30,000 plants per acre. A corn–winter rye–soybean treatment was initiated on those plots. Rye biomass averaged 1.5 and 4.2 dry tons/acre in 2011 and 2012, respectively, while the soybean crop averaged 56 bu/acre in 2011. These and other REAP results have also been used to support collaborative development of the Residue Management Tool by Agricultural Research Service (ARS) scientists and Department of Energy (DOE) engineers. The Tool is being deployed for beta-testing during the fall 2012 harvest season. Under Discovery non-Hypothesis 3.3, analyses for soil quality assessments for 14 Cropland Conservation Effects Assessment Project (CEAP), two Natural Resources Conservation Service Special Emphasis CEAP watersheds, and a University of New Hampshire organic transition farm were completed. A summary of the initial results was presented at the annual Soil and Water Conservation Society meetings in Ft. Worth, TX. Interpretation of the indicator data using the Soil Management Assessment Framework (SMAF) for six of the sites showed the soils to be functioning at between 55 and 95% of their potential for crop production. These soil quality results will help assess the sustainability of cropping systems.
1. Pros and cons of humic products unraveled. Humic compounds are natural products formed by decomposing organic (humus) materials in soils, coal, upland streams, lakes, and ocean sediments. Limited research has shown that applying these materials to plants may improve growth and other characteristics. The humic product industry has a small but sustained market, yet little formal evidence exists for the field efficacy of their products. To address this knowledge gap, ARS scientists in Ames, Iowa, measured the effects of one humic product on corn growth in multiple field experiments during three years. Grain weight increased in most farmers’ fields with product application as measured through plant samples collected by hand at physiological maturity; the few available yields measured by mechanical combine showed more subdued increases. In-season measurements showed improved plant growth and health with product application. Results indicated that humic products can improve corn growth, but extensive measurements are needed to establish the interactions of the humic product with environmental and management factors. Results will be shared with the humic products industry to serve as a case study for the type of documentation needed to validate their products.
2. Guidelines for corn stover harvest. Corn stover has been identified as a potential feedstock for producing bioenergy and/or other bioproducts but guidelines for sustainable harvest are needed. Four years of cooperative field research among ARS scientists in Ames, IA, POET-DSM, and Iowa State University showed that to sustain soil carbon levels and other critical soil functions, corn stover should not be harvested if average grain yields are less than 11 Mg/ha (175 bu/acre). This information supports other Renewable Energy Assessment Project team studies and is providing guidance to several companies striving to use corn stover for bioenergy or other bioproducts.
Karlen, D.L., Archer, D.W., Liska, A.J., Meyer, S. 2012. Energy issues affecting corn/soybean systems: Challenges for sustainable production. Council for Agricultural Science and Technology Issue Paper. Paper No. 48. Available: http://www.cast-science.org/publications/?energy_issues_affecting_cornsoybean_systems_challenges_for_sustainable_production&show=product&productID=52665.