Short-term effects of exogenous protease application on soil fertility with rice straw incorporation

Rice straw incorporation increases soil fertility in the long-term. However, it may cause N deficiency in the short-term. The aim of this study was to use exogenous protease to reduce N deficiency in short-term. A two factor incubation experiment was conducted to test the effects of protease addition (at six levels ranging from 0 to 3%) to the soil with or without incorporated rice straw at 5%. After a 120-day incubation period, soil protease activity, available N, available P and electrical conductivity of treatments with at least 0.5% added protease were significantly (P < 0.05) greater than the no-protease control, with increases ranging from 82.4 to 168.8, 35.3 to 52.3, 10.9 to 21.9, and 107.1 to 173.9%, respectively. Soil organic matter and pH of treatments with added protease were lower than the no-protease control. Without straw incorporation, protease amendments only affected the soil protease activity itself, not other soil properties. In an orthogonal experiment designed to test the effects of temperature (15-35 degrees C), pH (5.5-7.5), water content (40% field capacity to submerged), and protease concentration (1-3%), fuzzy comprehensive evaluation was used for overall consideration of soil fertility, the optimum conditions are as follows: temperature 35 degrees C, pH 7.5, protease concentration 1%, and 100% field capacity. When protease was added to soil under conditions similar to rice field conditions, soil fertility was only slightly lower than that under optimal conditions. It is concluded that protease can reduce N deficiency, the effects of protease are influenced by environmental conditions, and exogenous protease may be used in field operations. (C) 2010 Elsevier Masson SAS. All rights reserved.