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Use of soil nonexchangeable potassium by paddy rice with clay structural changes under long-term fertilizer management
Authors:Junta Yanai  Nanami Inoue  Atsushi Nakao  Masahiro Kasuya  Kaori Ando  Toshiya Oga  Takayuki Takayama  Hiroyuki Hasukawa  Kunihiko Takehisa  Akira Takamoto  Kazuki Togami  Tomoki Takahashi
Institution:1. Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto, Japan;2. Environment and Farm Management Division, Aichi Agricultural Research Center, Nagakute, Japan;3. Agricultural Technology Promotion Center of Shiga Prefecture, Omihachiman, Japan;4. Daisen Research Station, Tohoku Agricultural Research Center, National Agriculture and Food Research Organization, Daisen, Japan
Abstract:To prove the hypothesis that paddy rice utilizes soil nonexchangeable potassium (neK) and causes associated structural changes in clay minerals, K status and clay mineralogy of 22 surface soils from three paddy fields under long-term fertilizer management for 51–93 years were investigated. Soil neK content was determined as the difference between 1 mol L?1 hot HNO3 extractable K and 1 mol L?1 ammonium acetate exchangeable K. Clay mineralogy was identified by X-ray diffraction (XRD). The radiocesium interception potential (RIP), an index of frayed edge sites in the interlayer sites of 2:1 type clay minerals, was also determined. The neK contents under the -K and NPK treatments were considerably lower than those under the unfertilized treatment in all the fields, indicating the exploitation of soil neK by rice. XRD analysis of the clay samples revealed 7% shift from the 1.0 peak to 1.4 nm one under the -K treatment compared with the unfertilized one, and the amounts of neK were negatively correlated with those of RIP (p < .01), suggesting the expansion of interlayer spaces of the 2:1 type phyllosilicates such as mica due to the release of neK. In addition, the neK content positively correlated with K balance of the long-term experiments (p < .05). The differences of neK between unfertilized K and -K treatments corresponded to 22–157 kg K ha?1, or 0.42–1.68 kg K ha?1 year?1. In conclusion, utilization of considerable amount of soil neK under K depleted conditions should be considered to establish sustainable K management for paddy rice.
Keywords:mica  nonexchangeable potassium (neK)  paddy soils (soils of the paddy field)  radiocesium interception potential (RIP)  X-ray diffraction (XRD)
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