2012 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 release fertilizer, and during decomposition and mineralization of organic amendments including biofuel coproducts and animal manures. Formerly 5354-21660-001-06S (10/08). Soil water, temperature and conductivity sensors will be installed in irrigated potato field for real-time measurement and estimation of soil water mass balance. Biomass samples will be taken for evaluation of crop growth, nutrient distribution and validation of growth simulation model predictions.
A two-year field experiment under this cooperative agreement was completed in 2011. There were 10 treatments, 6 cover crop species (sunn hemp: SH; velvet bean: VB; sorghum sudangrass: SS; okra: OK; cowpea: CP; and caster bean: CB) in mono- and bi-culture (SS+SH; OK+CP; and CB+VB) and fallow as control with 4 replications each. These cover crops were mowed and incorporated into the soil, and snap beans (Inspiration) were grown. By the end of the experiment, we collected soil samples and performed chemical analysis for these samples during this year. Our research directly relates to sub-objective 1.A. of the related in-house project, "Evaluate the impacts of harvest of C3 and C4 grass perennial biomass crops and the removal of crop residues on carbon sequestration, nutrient dynamics, and soil quality in irrigated Pacific Northwest crop rotations". Results showed that total carbon (C), total nitrogen (N), and soil organic matter (SOM) contents of the soil varied significantly among cover crops and their mixtures. Total phosphorus (P); plant available P, exchangeable potassium (K), iron (Fe), and magnesium (Mg) contents of the soil varied significantly among treatments. Phosphorus fractions likewise varied significantly among treatments. Most of the P in the soil is calcium (Ca)-Mg bound P (74.77%), followed by residual P (8.04%), Fe-aluminum (Al) bound P (5.55%), organic P (2.29%), water soluble P (0.95%) and the lowest was exchangeable P (0.58%). The P fractionation recovery ranged from 78.8% - 102.6%. Among the leguminous cover crops, castor beans had the highest plant available P, Fe-Al bound P, residual P, P total and P sum. The lowest available P was observed in velvet beans. All of the P fractions were highest in okra and cowpea when planted together except with the organic P, which was highest in castor beans and velvet beans mixture. Two years of cover cropping is too short time to see the influence on the changes of chemical properties of the soil. Results however, are promising as evidenced by the significant differences among treatments. From the obtained results, it is evident that two years of cover cropping demonstrated some influence on P fractionation.