No abstract

Increasing use of N fertilizer for crop production necessitates more rapid estimates on N provided by the soil in order to prevent under-or overfertilization and their adverse effect on plant nutrition and environmental quality. A study was conducted to investigate the responses of arginine ammonification (AA), L-glutaminase activity (LG), soil N-mineralization indices, corn (Zea mays L.) crop-yield estimation, and corn N uptake to application of organic amendments. The relationships between corn N uptake and the microbial and enzymatic processes which are basically related to N mineralization in soil were also studied. The soil samples were collected from 0-15 cm depth of a calcareous soil that was annually treated with 0, 25, or 100 Mg ha -1 (dryweight basis) of sewage sludge and cow manure for 7 consecutive years. Soil total N (TN), potentially mineralizable N (N 0 ), and initial potential rates of N mineralization (kN 0 ) were significantly greater in sewage sludge-treated than in cow manure-treated soils. However, the amendment type did not influence soil organic C (SOC), AA, LG, and anaerobic index of N mineralization (N ana ). The application rates proportionally increased N-availability indices in soil. Corn N concentration and uptake were correlated with indices of mineralizable N. A multiple stepwise model using AA and N ana as parameters provided the best predictor of corn N concentration (R = 0.86, p < 0.001). Another model using only LG provided the best predictor of corn N uptake (R = 0.78, p < 0.001). This results showed that sewage-sludge and cow-manure application is readily reflected in certain soil biological properties and that the biological tests may be useful in predicting N mineralization and availability in soil.