where is profit ($ ha -1 crop -1 ); GP is the
average farm-gate price of rice ($ kg -1 ); Y is
the grain yield with nutrient applied (kg ha -1 );
Y 0 is the grain yield without nutrient applied
(kg ha -1 ); P F is the market price of fertilizer
nutrient ($ kg -1 ); and F is the amount of fertilizer
nutrient applied (kg ha -1 ).
Profits for different combinations of N, P, and
K fertilizer can be calculated and compared
using