2010 Annual Report 1a.Objectives (from AD-416) (i) Estimate biomass production and nutrient reserve in leguminous cover crops, i.e. sunn hemp, and velvetbean, under an arid temperate vs. humid tropical climatic condition in vegetable production systems. (ii) Estimate mineralization rates of the above cover crops and carbon sequestration rates under the above agroclimatic vegetable production systems. (iii) Trace gas emissions and ammonia volatilization with different nutrient and residue management practices in a vegetable rotation system. (iv) Estimate nutrient transformation, trace gas emissions, and carbon sequestration during decomposition and residue turnover from biofuel coproducts and other agricultural wastes. (v) Investigate real-time changes in soil water contents and temperature that influence the cover crops residue decomposition, N mineralization and transport, and carbon sequestration. (vi) Estimation of soil water mass balance to predict leaching of water and nutrients below the rootzone. (vii) Collection of field data for validation of potato growth simulation model in commercial growing conditions to incorporate nutrient and water dynamics component to enhance nutrient and water uptake efficiencies. 1b.Approach (from AD-416) Field studies will be conducted in Columbia Basin irrigated production region in WA (arid, temperate) and near Homestead, FL (humid, subtropical). Sunn hemp and velvetbean cover crops will be grown following the standard production practices for each of the above production regions. Total biomass production and nutrient reserves in each of the cover crops will be estimated. Following the incorporation of the cover crops, the decomposition of the residue, rate of mineralization, and carbon sequestration rate will be estimated. Trace gas emissions and ammonia volatilization will be evaluated under different fertilizers and residue management for potatoes, including fertigation, controlled resease fertilizer, and during decomposition and mineralization of organic amendments including biofuel coproducts and animal manures. Formerly 5354-21660-001-06S (10/08). 3.Progress Report Field experiments with different combinations of cover crops have shown the following results: (1) Sunn hemp can produce 15-20 Mg/ha of dry biomass in three months (July-September); (2) Mixture of legume and non-legume covercrops significantly increased the total amount of biomass compared to the monoculture; (3) Total N content in sunn hemp cover crop biomass is about 350 kg/ha in contrast to 50 kg/ha in sorghum sudangrass; (4) Soil fertility, especially N content, can be improved significantly by incorporation of legume cover crop residues, especially sunn hemp or velvetbean; (5) Legume cover crop residues mineralized faster than that of non-legume cover crops at the beginning, but there was no significant difference between legume vs. non-legume cover crops 4-12 months after incubation depending on the temperature; (6) Rate of mineralization was greater in a Quincy fine sand (from Washington) as compared to that in a Krome gravelly loam soil from Florida; (7) The mineralization rate increased dramatically by increasing the temperature from 20 to 30 °C; and (8) Mineralization rate was extremely slow when the plant residue was applied to soil surface without incorporation. This project was monitored via email and phone calls with the cooperator. The agreement was established in support of Objective 2B, the goal being to investigate Mechanisms of carbon and nitrogen cycling in potato production systems.