Fig. 7 (a) Chloroform-released P and (b) exchangeable PO₄–P in the soil of channels receiving inputs of either no P, the intermediate P level, or the highest P level. Solid points represent Site 1 and hollow points represent Site 2. Lines connect the average of the values for the two sites. Points are plotted for the 0- to 3-, 6- to 9-, 12- to 15-, and 21- to 24-cm depth increments