Carbon-nitrogen interaction in field crop production

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Abstract
A carbon-nitrogen interaction model during growth was developed as follows: DM = DM0e(CNI×N) for Gramineae (rice, wheat, and maize) and root crops (potato, sweet potato, and sugar beet) and DM = DM0 + CNI′ × 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 (Nh), indicating that the relationship between the CNI or CNI′-value and Nh fitted to a hyperbolic curve as follows: CNI = l/(aNh+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 CNF value of Leguminosae was almost constant regardless of Nh. 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).