Biochemical properties of Roi Et and Phimai soil receiving organic debris
1999
Patcharee Saenjan (Khon Kaen Univ., Khon Kaen (Thailand). Faculty of Agriculture. Dept. of Soil Science)
Laboratory experiment to determine changes in chemical and biochemical properties of Roi Et and Phimai paddy soil receiving organic debris was conducted for both under field capacity and under submerged condition. The organic debris used were fresh Sesbaia rostrata, rice straw and cow dung. The soil samples were incubated under field capacity and were analyzed for cumulative content of CO2, NH4+ and NO3- in the soil of 0-2.5 and 2.5-5 cm depths. The same treatments were incubated under submerged condition and were analyzed for pH, NH4+, Mn2+, Fe2+ and organic acid. In both soils, incorporation of organic debris increased NH4+ concentration in both aerobic and anaerobic conditions. Decomposition of organic debris increased in this order: Sesbania rice straw cow dung control. The amount of CO2 and HN4+ were higher in Phimai paddy soil than in Roi Et soil. NO3- was increased while NH4+ was decreased in aerobic soil indicated nitrification. After submerging the soil, pH, NH4+, Mn2+ and Fe2+ rose. This occurred more intense in Phimai soil than in Roi Et soil, especially, when organic debris were incorporated. Successive manganous and ferrous formation indicated maganese reduction and ferric reduction in submerged soil. Only acetic acid was detected as an intermediate product of organic matter decomposition. The amount of this acid increased to the maximum of 1.0 mM/100 g soil at 10 days after submergence in Roi Et soil receiving Sesbania and of 1.5 mM/100 g soil at 7 days in Phimai soil with Sesbania treatment, and finally decresed to the lowest amount at 24 days after submergence. This suggests that rice transplanting should begin at 2 weeks after incorporation of organic debris.
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