Abstract
The comparison were made on R^2 value of the regressions of the various plant parameters (Panicum maximum cv. Gatton) against P-levels obtained in the acid soil and in the alkali soil with six P-tests ; Bray-1, Bray-2, Truog, Truog modified, Olsen, and Ion exchange resine methods. The P-tests which showed higher R^2 value in the regressions of P-levels against rates of P-fertilizer applications, relative plant top DM yields, and relative plant P-uptake were Bray-2, Truog, Truog modified and IER methods, Truog, Truog modified and IER methods, and Bray-2, Truog modified and IER methods, respectively. With the above results, Truog, Truog modified and IER methods were judged as suitable methods for estimating available-P in the soils of South-Western Islands of Japan. However, in view of the range and coefficients of covariation of soil available-P obtained with above three methods, Truog modified method was considered to be the most convinient for evaluating P-response of various pasture plants and for predicting a precise rate of P-application required for the optimum plant growth.
