Disentangling the effect of environmental factors on yield and nitrogen uptake of irrigated rice in Asia

Rice yield is the result of the interaction between genotype (cultivar characteristics), environment (climate and soil conditions), and management. Few studies have attempted to isolate the contribution of each of these factors. Here the rice growth model ORYZA2000 was used to analyse the variation in yield, nitrogen (N) uptake, and internal N use efficiency (INUE, grain yield per unit total crop N uptake) of rice in different environments. First, ORYZA2000 was calibrated and evaluated using an empirical data set that spanned three varieties, three years, and eight locations in Asia. Next, we used the model to investigate the relative contribution of indigenous soil N and external N supply and of the weather factors temperature and radiation to observed variation in yield. With normalized root mean square errors (RMSEn) of 6-16%, ORYZA2000 satisfactorily simulated crop biomass, yield, N uptake, and INUE, that strongly varied among genotypes and locations. Environmental factors contributed differentially to yield, N uptake, and INUE, and their contributions were modified by N management. Indigenous soil N supply affected yield and INUE more strongly than weather conditions at low fertilizer N rates, but its influence was less pronounced at higher fertilizer N rates. Under both, low and high fertilizer N rates, indigenous soil N supply affected N uptake more than weather conditions did. Temperature contributed more than radiation to the variation in yield, N uptake, and INUE. Results suggest that N fertilizer management should take into account indigenous soil N supply, while temperature is the major factor in the selection of genotypes and sowing dates in maximizing rice yield.