Exploring options to grow rice using less water in northern China using a modelling approach - I. Field experiments and model evaluation

China's grain basket in the North China Plain is threatened by increasing water scarcity and there is an urgent need to develop water-saving irrigation strategies. Water savings in rice can be realized by alternate wetting and drying (AWD) under lowland conditions, or by aerobic rice in which the crop is grown under nonflooded conditions with supplemental irrigation. Field experimentation and simulation modelling are a powerful combination to understand complex crop-water interactions and to extrapolate site-specific empirical results to other environments and conditions. In this paper, we present results from 4 years of field experiments on AWD and aerobic rice in 2001-2004 near Kaifeng, Henan Province, China. The experimental data were used to parameterize and evaluate the rice growth model ORYZA2000. A subsequent paper reports on the extrapolation of the experimental results using ORYZA2000 and on farmer-participatory testing of aerobic rice. In the lowland area of the study site, rice yields under flooded conditions were around 8000 kg ha(-1) with 900 mm total (rain, irrigation) water input. Irrigation water savings were 40-70% without any yield loss by applying AWD. In the upland area of the study site, aerobic rice yielded 2400-3600 kg ha(-1), using 750-1100 mm total water input. ORYZA2000 satisfactorily reproduced the dynamics in measured crop variables (biomass, leaf area, N uptake) and soil water variables (ponded water depth, soil water tension). The root mean square error of predicted yield was 11% for lowland rice and 19% for aerobic rice, which was only one and a half times the error in the measured values. We concluded that ORYZA2000 is sufficiently accurate to extrapolate our results on AWD and aerobic rice to different management and environmental conditions in our study area. (c) 2006 Elsevier B.V. All rights reserved.