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CO2 flux was measured continuously using the eddy covariance technique in a wheatmaize rotation system in the North China Plains from October 2002 to October 2006. The annual and seasonal variation of ecosystem respiration and the bio-environmental controls on them were investigated. The results show that ecosystem respiration (Rec) in the cropland increased exponentially with soil temperature at 5 cm depth. The temperature sensitivity coefficient (Q10) for ecosystem respiration varied from 3.5 to 5.4 for wheat and from 2.4 to 4.5 for maize. In the wheat growing season, monthly average R0 (ecosystem respiration at 0°C) increased linearly with soil temperature and logarithmically with leaf area index (LAI). Monthly average Q10 decreased logarithmically with R0. Residual Rec was significantly correlated with LAI. After considering LAI, the modified Q10 model could estimate Rec better than before. The simulation results show that annual ecosystem respiration in the wheat-maize rotation system in the North China Plains was 1327, 1348, 1040 and 1171 gC m-2 yr-1 for the 4 years of the study. As a 4-year average, seasonal mean ecosystem respiration in wheat (2.60 gC m-2 day-1) was much lower than in maize (6.09 gC m-2 day-1). However, integrated ecosystem respiration for the wheat growing season (566 gC m-2) was slightly higher than that for maize (520 gC m-2). These account for 46.4 and 42.6% of the annual values, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Limited precipitation restricts crop yield in the North China Plain, where high level of production depends largely on irrigation. Establishing the optimal irrigation scheduling according to the crop water requirement (CWR) and precipitation is the key factor to achieve rational water use. Precipitation data collected for about 40 years were employed to analyze the long-term trend, and weather data from 1984 to 2005 were used to estimate the CWR and irrigation water requirements (IWR). Field experiments were performed at the Luancheng Station from 1997 to 2005 to calculate the soil water consumption and water use efficiency (WUE). The results showed the CWR for winter wheat and summer maize were similar and about 430mm, while the IWR ranged from 247 to 370mm and 0 to 336mm at the 25% and 75% precipitation exceedance probabilities for winter wheat and summer maize, respectively. The irrigation applied varied in the different rainfall years and the optimal irrigation amount was about 186, 161 and 99mm for winter wheat and 134, 88 and 0mm for summer maize in the dry, normal and wet seasons, respectively. However, as precipitation reduces over time especially during the maize growing periods, development of water-saving management practices for sustainable agriculture into the future is imperative. [Copyright &y& Elsevier]