Parameters determining yield of field crops in relation to the amount of nitrogen absorbed

Several field crops were grown at different nitrogen levels during 6 y, and under combinations of nitrogen levels and plant density . Then the parameters which determine the economic yield (Ye) were evaluated by using the following formula . Ye=Yb × HI(DM), Ye=Yb(N) × HI(N)/Nc(h .o.) × 100, and Ye=Gn × Gw, where Yb is the biological yield ; HI(DM) is the harvest index of dry matter; HI(N) is the harvest index of nitrogen ; Yb(N) is the amount of nitrogen accumulated in plants; Nc(h.o.) is the nitrogen content of harvesting organs; Gn is the number of grains or tubers ; and Gw is the one-grain weight or one-tuber weight. As the parameters showed a close relationship with Yb(N) with few exceptions, they were expressed by the function of Yb(N) as follows . HI(DM)= a,Yb(N)+b,, HI(N)=a2Yb(N)+b2 7 Nc(h.o.)=a3Yb(N)+b3, Gn=a4ln(Yb(N))+ b4, Gw=a5,Yb(N)+b5 , where, a1, a2, a3, a4, a5, b1, b2, b3, b4, and b5, were constants. The HI(DM) and HI(N) were significantly constant in rice, maize, soybean, potato, and sugar beet because the a1, and a2 values were nearly zero, and HI(N) decreased with the increase of Yb(N) only in wheat . As Nc(h .o.) increased with the increase of Yb(N), Nc(h .o.) was the main factor determining the decrease of Ye when Yb(N) increased. As the value of a4 in all the crops was significantly stable, unlike the value of a5, in some crops, Ye was mainly determined by Gn which was affected by Yb(N). Thus, the Yb, HI(DM), III(N), Nc(h .o.) parameters related to Yb(N) were useful for analyzing Ye.