The objective of this investigation was to compare extracting procedures which might be superior to the Morgan method for predicting the phosphorus status of soils in Pennsylvania.
The first experiment involved the Ap horizons of 161 soil types. Of these, 44 soils were selected for additional experiments. Some of the soils tested either very high or very low in P by all methods, some tested high by one or more methods but not by other methods, and some fixed either high or low percentages of the added P against extraction by one or more of the methods.
With respect to the amounts of P removed from soils, the extractants ranked in the order Purdue > Bray no. 1 > Morgan > Experimental > CaCl2. The respective extractants removed about 52, 38, 8, 4, and 1% of the P which was added and allowed to react with the soils. In general, the test values obtained by one method were not very closely related to values obtained by other methods for these soils.
The Bray no. 1 method was most accurate for predicting plant uptake of P while the Purdue method proposed by Al-Abbas and Barber was least accurate.