RELATING PHOSPHORUS QUANTITY, INTENSITY, AND BUFFER CAPACITY TO PHOSPHORUS UPTAKE

The short-term (25 days) phosphorus (P) uptake by maize has been repor ted to be most strongly correlated with measurements of P intensity in soil. Correlations of P uptake with bicarbonate-extractable P (a meas ure of the quantity factor) were improved when indices of P buffer cap acity were included, but not to the extent obtained with the direct me asure of P intensity. Thus, one might infer that measurements of the q uantity factor and P buffer capacity were less satisfactory for descri bing P availability. It is now shown that this conclusion results enti rely from the model fitted to the data. By using a multiplicative rath er than additive model, it is shown that bicarbonate-extractable P in combination with measures of P buffer capacity can describe the P upta ke data equally as well as a direct measurement of P intensity.