Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/1996
Publication Date: N/A
Interpretive Summary: Nitrogen fertilizer recommendations could be improved with the adoption of rapid, accurate soil testing procedures that account for nitrogen mineralization due to soil microorganism activity. Several laboratory methods were evaluated for their reliability in predicting N mineralization. Nitrogen mineralization from several agricultural soils varying in texture and soil organic matter content was highly related to the amount of carbon dioxide evolved as a result of microbial activity. This simple biological method should make soil testing for N mineralization more widely adaptable and provide a rapid, reliable procedure to more accurately predict N fertilizer requirements of crops. Improved fertilizer recommendations would increase farmers' net returns by avoiding costly overfertilization and underfertilization and decrease environmental risks to water quality.
Technical Abstract: Routine soil testing procedures that are rapid and precise are needed to evaluate soils for their potential to mineralize C and N. Our objectives were to determine the optimum preincubation time after rewetting of dried soil for estimating soil microbial biomass carbon (SMBC) and to identify a quick, reliable predictor of soil N mineralization potential. Biochemical determinations included arginine ammonification, substrate-induced respiration (SIR), cumulative C and net N mineralization, and SMBC using the chloroform fumigation-incubation (CFI) method performed on (i) field-moist soil and (ii) soil that was air-dried, rewetted, and preincubated for 0.2, 1, 3, 6, 10, and 15 d. AA and SIR determinations on dried soil were highly variable making longer preincubation periods necessary. Carbon mineralization during all preincubation periods was highly correlated to (i) SMBC using CFI determined on field-moist and dried soil with all preincubation periods and (ii) net N mineralization during 21 d for the Weswood soil, as well as for seven additional soil series each having five to eight levels of SOC. Carbon dioxide evolved during the first day after rewetting of dried soil is recommended for rapid estimation of SMBC and potential N mineralization.