Potassium fertility of Thai soils and management practices for agricultural sustainability
1996
Amnat Suwanarit (Kasetsart Univ., Bangkok (Thailand). Faculty of Agriculture. Dept. of Soil Science)
Soils of most of the areas in Thailand have kaolinite as the dominant clay mineral suggesting that soils of most of the areas are low in K. Results of chemical analyses of sample soils also support this. Regosols and Hydromorphic Regosols generally have the lowest total-K and available-K contents and Gley Podzolic and Hydromorphic Gley Podzolic soils have the second lowest K contents. Alluvial soils generally have the highest K contents. Results of studies with different crops in most cases showed no responses in crop yields to K fertilization. This was presumably due to the farmers' selection of crops according to fertility of the soils. Results of studies showed that peanut gave the lowest critical level of K in soils (35 mg NH4OAc-extractable K/kg) whereas cotton gave the highest one (around 120 mg NH4OAc-extractable K/kg). Soybean, cassava and kenaf gave rather similar critical levels (45-55 mg NH4OAc-extractable K/kg). Rice and corn also gave similar critical levels (around 74 mg NH4OAc-extractable K/kg). Besides K status of soils, balance of nutrients, crop cultivar and time of application are shown to affect responses of crops to K fertilizer. It is also pointed out that other factors may also affect the responses. In the general fertilizer recommendations, K application is recommended for all crops grown on sandy soils. On loamy soils, K fertilization is recommended for all of the crops except corn and sorghum. On black clayey soils K fertilizer is recommended for snow pea, string bean, chili, all vegetables, tobacco and fruit trees but not for rice, corn sorghum and cotton. On red clayey soils, K fertilizer is recommended for sugarcane, cotton, snow pea, string bean, all vegetables, tobacco and fruit trees but not for rice, corn sorghum, soybean and mungbean.
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