CARBON-NITROGEN INTERACTION IN FIELD CROP PRODUCTION

A carbon-nitrogen interaction model during growth was developed as follows: DM=DM0e(CNIxN) for Gramineae (rice, wheat, and maize) and root crops (potato, sweet potato, and sugar beet) and DM = DM0 + CNI'X N for Leguminosae (soybean, field bean, and adzuki bean), where, DM is the dry weight of plant, N is the amount of nitrogen accumulated in plant, DM0 is the initial amount of dry weight (obtained by the regression method), and CNI or CNI' is the carbon-nitrogen index. The CNI or CNI'-value changed with the amount of nitrogen absorbed at the time of harvest (N(h)), indicating that the relationship between the CNI or CNI'-value and N(h) fitted to a hyperbolic curve as follows: CNI=1/(aN(h)+b), where, a and b are the coefficients of the equation. As the coefficient a of Leguminosae (soybean, field bean, and adzuki bean) was nearly zero, the CNI' value of Leguminosae was almost constant regardless of N(h). The coefficient a was very similar among rice, maize, potato, and sugar beet. Thus, it is assumed that the carbon-nitrogen interaction was significantly different between Leguminosae and other crops (Gramineae and root crops).