It has long been concerned how crop water use efficiency (WUE) responds to climate change. Most of existing researches have emphasized the impact of single climate factor but have paid less attention to the effect of developed agronomic measures on crop WUE. Based on the long-term field observations/experiments data, we investigated the changing responses of crop WUE to climate variables (temperature and precipitation) and agronomic practices (fertilization and cropping patterns) in the semi-arid area of northern China (SAC) during two periods, 1983–1999 and 2000–2010 (drier and warmer). Our results suggest that crop WUE was an intrinsical system sensitive to climate change and agronomic measures. Crops tend to reach the maximum WUE (WUEmax) in warm-dry environment while reach the stable minimum WUE (WUEmin) in warm-wet environment, with a difference between WUEmax and WUEmin ranging from 29.0%-55.5%. Changes in temperature and precipitation in the past three decades jointly enhanced crop WUE by 8.1%-30.6%. Elevated fertilizer and rotation cropping would increase crop WUE by 5.6–11.0% and 19.5–92.9%, respectively. These results indicate crop has the resilience by adjusting WUE, which is not only able to respond to subsequent periods of favorable water balance but also to tolerate the drought stress, and reasonable agronomic practices could enhance this resilience. However, this capacity would break down under impact of climate changes and unconscionable agronomic practices (e.g. excessive N/P/K fertilizer or traditional continuous cropping). Based on the findings in this study, a conceptual crop WUE model is constructed to indicate the threshold of crop resilience, which could help the farmer develop appropriate strategies in adapting the adverse impacts of climate warming.

SUMMARY: A cropping system is the consequence of environmental and socio-economic conditions that determine the intensity of agricultural land use. Accurate information on regional land use intensity and changes in land use intensity is important for food security and sustainable resource management in China. Therefore, a better understanding of the spatial and temporal changes in arable land use intensity (ALUI) based on the cropping system used is essential to comprehend the changes in land use and the sustainability of the food system. The purpose of the present study was to investigate the spatial difference in ALUI and how it has changed in China by comparing data on cropping systems from 1985 and 2005. The basic cropping system data were acquired from the 1985 reference book and the 2005 national land use investigation. The ALUI was defined by the application of inputs (irrigation water and fertilizer) to arable land and the duration of disturbances (the duration of cultivation and the frequency of cropping), and it was calculated using the information entropy approach at the cropping region scale (cropping region being defined by the geographical and climatic conditions at the beginning of the 1980s). Spatial and temporal changes in the ALUI in China over the past two decades were observed and analysed. The results indicated a clear pattern in ALUI, increasing from the north to the south in 2005. Furthermore, the ALUI significantly increased after the 1980s, but the rate of increase was lower in the south than in the north. The most intensive land use in 1985 was in the area of the lower reach of the Yangtze and Huai Rivers, and it expanded northwards towards the Huang-Huai-Hai plain in 2005. The large increase in intensity in the northern single-cropping regions was strongly associated with a rapid increase in inputs and longer duration of cultivation. Decreases in duration of cultivation and planting area helped slow the ALUI increase in multiple cropping regions, which were concentrated in coastal and economically developed regions where more fertile soil and suitable climates existed, allowing the growth of multiple crops. These results suggested that a decrease in the planting area and a slow increase in the ALUI in the lower reaches of the Yangtze River, South China, Southeast China and Northeast China should be of concern, but land use in some western regions should maintain the land production capacity to build sustainable cropping. In the future, it will be necessary to produce more food in a more sustainable way.