N mineralization process of the surface soils under shifting cultivation in northern Thailand |
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| Authors: | Sota Tanaka Shinya Funakawa Thammanoon Kaewkhongka Koyo Yonebayashi |
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| Institution: | 1. Faculty of Agriculture , Kochi University , Nankoku , 783-8502 , Japan;2. Faculty of Agriculture , Kyoto Prefectural University , Kyoto , 606-8522 , Japan;3. Faculty of Agriculture , Kyoto University , Kyoto , 606-8502 , Japan;4. Department of Agriculture , Bangkok , 10900 , Thailand;5. Faculty of Agriculture , Kyoto Prefectural University , Kyoto , 606-8522 , Japan |
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| Abstract: | N mineralization process (ammonification plus nitrification) in the surface 0-5 cm soil layers under shifting cultivation in northern Thailand was studied. Labile pool of organic matter extracted with a K2S04 solution at 1l0°C in an autoclave (fraction A) or by shaking at room temperature (fraction B) was used as factor to evaluate the N mineralization process which was examined in an incubation experiment. In the soils, in which the N mineralization pattern was fitted to a first order kinetics model, the content of (organic + NH4 +)-N in fraction B determined the initial rate of N mineralization. The soils, which showed a short lag time of less than 7 d both in the N mineralization and nitrification processes, had a high ratio of organic C to (organic + NH4 +)-N in fraction B, exceeding the value of 7. The soils, which showed a long lag time of more than 7 d only in the nitrification process, had a low pH(KCI) (less than 4.2). Thus, the rate of N mineralization was affected by the labile pool in fraction B or soil pH. On the other hand, there was a correlation between the N 0 + N max (inorganic N at 0 d + maximum amount of mineralizable N) value and the labile pool in the fraction A, suggesting that the N 0 + N max value depended on the contents of the labile pool. |
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| Keywords: | labile pool of organic matter nitrification N mineralization shifting cultivation |
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