Location: Soil, Water & Air Resources Research
Project Number: 5030-12000-015-20-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jan 1, 2015
End Date: Dec 31, 2018
Determine whether the degree of soil nitrogen saturation or the degree of soil carbon saturation affect further soil accumulation of carbon and soil release of nitrogen into plant-available forms, and determine the interactions between the degrees of soil nitrogen and carbon saturations.
Project collaborators will maintain corn-based field experiments on soils that differ in their degree of saturation with either carbon storage or nitrogen storage. Collaborators will measure grain yield, nutrient uptake, and other relevant crop growth parameters. Collaborators will collect multiple soil samplings during each growing season and analyze them for release of mineralizable nitrogen, total nitrogen content, and total organic carbon content. Release patterns of soil carbon will be investigated by partitioning soil carbon into fractions that differ widely in their respective ages and turnover rates. Specifically, USDA-ARS staff will supervise the physical fractionation of soil into aggregate size classes. From selected aggregate classes, USDA staff will supervise the extraction of a low-density, plant-like fraction of soil carbon and of two chemically extracted fractions through a procedure developed previously by USDA-ARS staff–the mobile humic acid (a relatively young humus fraction) and the calcium humates (an older, chemically protected humus pool). All extracted fractions will be measured for mass and concentrations of carbon and nitrogen. Changes in these parameters within a growing season and among years will enable the partitioning of soil carbon sequestration into either accumulation of partially degraded plant litter, chemical stabilization into more humified fractions, or protection by aggregation. USDA-ARS staff will obtain further information on the source and type of sequestered C by determining its chemical nature. USDA-ARS staff will supervise the analysis of all extracted fractions by gas and liquid chromatographic techniques for their respective contents of individual amino acids and amino sugars, carbohydrates, phenols, and fatty acids. Certain amino sugars and carbohydrates are considered to be from either plant origin or microbial origin. Certain fatty acids have been interpreted as biomarkers of root-derived material and others as biomarkers of shoot-derived material. Ratios of such source-specific compounds can be calculated to identify the likely source materials for a given carbon fraction and for sequestered carbon. These results will determine whether the degree of soil nitrogen saturation or soil carbon saturation affects the stabilization and cycling of specific crop or microbial materials and whether the intrinsic chemical nature of materials promotes their stabilization or cycling in soil.