Fig. 4. The proportion of unavailable P (UP) in total P (TP) relative to soil texture and TP. The fields are shown in order of finest to coarsest texture based on sand content; the actual value can be found in Table 1. The data on each of the plots represent the overall mean for the corresponding field for the study period. The regression lines have the following equations: %UP = 91.1 – 0.273(%Sand); %UP = 89.7 – 36.7(TP).