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United States Department of Agriculture

Agricultural Research Service



2013 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.

3. Progress Report:
This project contributes to in-house Objective 1B: "Determine the efficacy of co-products from agricultural-based energy production on weed and disease control and soil fertility improvement in irrigated crop production systems". A growth chamber and a field experiments were conducted under this cooperative agreement. For the growth chamber trial, cover crops were triticale, ryegrass, mustard, bellbean, purple vetch, and white clover. These cover crops were grown in two different soils, Quincy fine sand from Prosser, Washington, and Krome gravelly loam from Homestead, FL, in three growth chambers. The growth chambers were set at 25/20 oC, 15/10 oC, and 10/8 oC (day/night), respectively, to simulate fall, spring, and winter climates. Soil samples were collected before and after the experiments for carbon (C) and nitrogen (N) analyses. Cover crops were sampled for above ground biomass determination and chemical analysis for total C and N prior to terminating and then keeping plant residues on the surface of the soil. Results showed that controlling temperature at 10/8 oC (day/night) can significantly reduce the accumulation of cover crop biomass compared with 25/20 oC and 15/10 oC. Plants in Quincy fine sandy soil produced more quantity of biomass than those in Krome gravelly loamy soil, which is attributed to the variation in soil fertility. Regardless of soil and temperature, triticale, ryegrass, and bell bean produced greater amounts of biomass than did mustard, and purple vetch. White clover had the lowest quantity of biomass produced. However, in Krome gravelly loamy soil, triticale had the greatest quantity of aboveground biomass, and in the sandy soil, bellbean produced more biomass than other crops especially at 25/20 degree C (day/night) temperature. For the field experiment, there were ten treatments, six cover crop species (sunn hemp: SH; velvetbean: 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. Cover crops were mowed and incorporated into the soil, and snap beans (Inspiration) were grown. By the end of each growing season, soil samples were collected and analyzed. Results showed that total C, total N, and soil organic matter (SOM) contents of the soil varied significantly among cover crops and their mixtures. Total P, plant available P, exchangeable K, Fe, and Mg contents of the soil varied significantly among treatments. Phosphorus fractions likewise varied significantly among treatments. Most of the P in the soil is Ca-Mg bound P (74.77%), followed by residual P (8.04%), Total P [NaOH digested] (7.82%), Fe-Al bound P (5.55%), organic P (2.29%), water soluble P (0.95%) and the lowest was exchangeable P (0.58%).

4. Accomplishments

Last Modified: 05/25/2017
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