Soil Nitrogen Mineralization Potential for Improved Fertilizer Recommendations and Decreased Nitrate Contamination of Groundwater
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In order to prevent overfertilization, which could lead to groundwater contamination, rapid and accurate soil testing procedures are needed to evaluate agricultural surface soils for their potential to mineralize C and N. Our objectives were to determine optimum conditions for estimating soil microbial biomass (SMB) from previously dried soils and to identify a quick, reliable biochemical predictor of soil N mineralization potential. Initial evaluations were conducted on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) with five levels of soil organic C (SOC) using (i) fresh soil, and (ii) soil that was air-dried, rewetted, and pre-incubated for 0.2, 1, 3, 6, 10, and 15 d. Procedures to estimate C and N mineralization potentials included arginine ammonification (AA), substrate-induced respiration (SIR), cumulative C and net N mineralization, and soil microbial biomass carbon (SMBC) using the chloroform fumigation-incubation (CFI) method. Carbon mineralization was highly correlated to (i) SMBC using CFI determined on fresh and dried soil and (ii) net N mineralization during 21 d for the Weswood soil, as well as for seven additional soil types with 5 to 8 levels of SOC each. Measurement of CO2-C evolved during the first day after rewetting of dried soil is recommended for rapid estimation of SMBC and potential N mineralization because of its simplicity and precision.