报告题目：Changes in the soil C and N contents, and their mineralization potentials in a rice paddy after long-term application of inorganic fertilizers and organic matters

　　报 告 人：Dr. Weiguo Cheng

　　单 位：日本山形大学农学部

　　报告时间：2016年01月21日上午09:30

　　报告地点：LAPC和融楼二楼会议室

　　Abstract

　　A long-term experiment on combined inorganic fertilizer and organic matters management in paddy rice cultivation began in May 1982 in Yamagata, northeastern Japan. After the 31st harvest, soil samples were collected from five types of fertilization treatments [1) PK, 2) NPK, 3) NPK + 6 Mg ha-1 rice straw (RS), 4) NPK + 10 Mg ha-1 rice straw compost (CM1), and 5) NPK + 30 Mg ha-1 rice straw compost (CM3)], at 5 soil depths (0-5, 5-10, 10-15, 15-20 and 20-25 cm), to assess the changes in soil chemical properties including the soil organic C and C decomposition potential, total N and N mineralization potential resulting from long-term organic matter addition. The C decomposition potential was assessed based on the CH4 and CO2 produced while the N mineralization potential was determined from the KCl-extractable NH4-N, after 2, 4, 6 and 8 weeks of anaerobic incubation at 30 oC in the laboratory. The pH decreased significantly only at the higher compost rate of 30 Mg ha-1, while EC increased in all the OM treatments. Available P significantly increased in the CM1 and CM3 treatments by 55.1 and 86.4%. Compared to NPK treatment, SOC in the 0-25-cm soil layer increased by 67.3, 21.0 and10.8% and TN increased by 64.2, 19.7 and 10.6%, in CM3, RS, and CM1 respectively, and SOC and TN showed a slight reduction in the PK treatment by 5.2 and 5.7%, respectively. Applying rice straw compost (10 Mg ha-1) instead of rice straw (6 Mg ha-1) to rice paddies reduced methane production by about 19% after the soils were measured under 8 weeks of anaerobic incubation at 30 oC. Soil C decomposition potential (Co) and N mineralization potential (No) were highly correlated with the SOC and TN contents. The mean ratio of Co/No was 4.49, lower than the mean ratio of SOC/TN (13.49) for all treatments, which indicated that the easily decomposed organic matter was from soil microbial biomass and soil proteins.