Effects of nitrogen input and climate trends on provincial rice yields in China between 1961 and 2003: quantitative evaluation using a crop model

Analyses of the technological and climatic factors that influence regional yield can provide insights into how production systems can be improved in the future. We analyzed the effects of changes in climate and nitrogen input on the time course of rice yields of nine rice-producing provinces in China for the period between 1961 and 2003. We developed a regional-scale model that considered both climate and nitrogen flow in the rice paddy. Observed yields (Y (obs)) tripled during the period, of which 65 % of the increase was accounted for by the estimated yield (Y (est)) based on changes in nitrogen input and climate. The remaining 35 % was attributed to other technological factors (alpha = Y (obs)/Y (est)), which include improvements in cultivars and pest management, for example. Contribution of alpha became pronounced after 1980 and accounted for 69 and 90 % of the yield increases in the 1980s and 1990s, respectively. Nitrogen input had much greater impacts on Y (est) (90 %) than did climate, but Y (est)/nitrogen input dropped substantially. Significant positive effects were observed for CO2 fertilization effects, which differed significantly among provinces; their relative contribution to the increase in Y (est) ranged from 1.0 to 7.4 %. The effect of temperature change on Y (est) was negative and significant in three provinces, but not for the overall average. To meet future rice demand and to improve nitrogen use efficiency, full use of possible positive interactions among cultivars, nitrogen management, and climate is required.