Fig. 4. The decline in Mehlich-3 extractable soil P of a mixture of 5 g of 0- to 5-cm and 15 g of 5- to 20-cm depth samples (i.e., 1:3 ratio) compared with 0- to 5-cm samples as a function of P sorption maximum of soil from the 5- to 20-cm depth for the 18 Oklahoma and Pennsylvania profiles.