The peak output of rice can be calculated from the basic fertility of soil with an equation proposed by the authors.In this paper,an additional equation to calculate the requirement of N for the predicted maximum yield of rice are proposed as follows:
N_R=(0.018(Y-1.05X)/E_F
where X is the yield of rice on certain rice field without fertilization,Y,the maximum obtainable yield of rice on the same field well fertilized.N,nitrogen requirement for yield Y,E_r,efficiency of the fertilizer applied.Experiments has shown that the eqation a practicable.