If Soil Test Results for P Are Available,the Optimum Amount

If soil test results for P are available,the optimum amount of P fertilizer to apply to a crop can be best recommended by __________.

A) comparing the cost of P fertilizer to the yield responses measured in the past when P was applied to similar soils with similar soil test P levels
B) subtracting the available soil test P from the total P uptake for the desired yield goal
C) subtracting the soil test P level measured from the soil test P level considered to be on the border of "high" and "very high"
D) calculating the amount of P needed to bring the ratios of soil test P to N,P to K,and P to Mg into balance with the proper ratio for the type of soil in question
E) these days,all four of the above a done,in order,by a computer program