Define the term - soil heterogeneity

The ratings seem rather arbitrary and empirical but are meant to get a reasonable yield. Outputs for different doses of fertilizers are obtained from the response.

On the basis of costs of input and outputs, the following parameters  may be derived,   

        
(i) maximum yield

(ii) maximum profit per hectare

(iii) maximum rate of return per rupee of investment

(iv) minimum profitable application, and used by a farmer to make his choice. Recommendations of fertilizers  are valid to the  extent that the soil sample collected for testing represents the soil of the area of operation. In case of doubt or wide soil heterogeneity, a large number of soil samples should be tested.