Soil Test Methods and Critical Limits of Potassium in Soil and Plants for Wheat Grown in Typic Ustochrepts

A greenhouse experiment was conducted with wheat (friticum aestivum) in 30 soils (Typic Ustochrepts) of Uttari Series of Kanpur, to evaluate relative efficacy of soil test methods for K and to establish critical limits of K in soil and plants. Multilocation field experiments were also conducted on cultivators fields to verify the differences in responses to added K in relation to soil test values and the critical limits of K in soils established through field and greenhouse experiments. The extraction capacities of the fourteen extractants were different, being highest for boiling HNO₃ and lowest for 0.01M CaCl. The quantities of K desorbed by boiling 1M HNO₃ showed highest degree of correlation with 0.5N acetic acid and lowest with 0.13M HCl. In view of the fact that responses to added K in soils of varying 1M NH₄ OAc (pH 7.0) status were modified by the 1M HNO₃ soluble K content of soils, the critical limits of K were established taking into consideration both exchangeable and non-exchangeable K status of the soils. Under greenhouse conditions responses to K were significant only up to soils testing medium-high in both exchangeable and non-exchangeable K. Responses to K under field conditions were significant on soils testing medium in respect of both exchangeable and non-exchangeable K. Apparently, the critical limit recorded under field conditions is slightly lower than of greenhouse conditions. Critical concentrationofKin 6-week-old plants of wheatwas 2.7 per cent.