Influence of rainfall in summer fallow period on water and nitrogen use efficiency of winter wheat on Loess plateau

Abstract: Due to low rainfall, intense runoff, deep loess deposits, low water tables as well as poor land management, soil is often dry on the Loess Plateau. Precipitation is very important for crops, especially the winter wheat. However, it is unknown about the impacts of rainfall in summer fallow period on soil water replenishment and growth of following crops. To clarify this problem, this study carried out field experiments from 2006 to 2010 in Changwu city of Shanxi province. Winter wheat was Chanhan 58. The field plots were 4 m in width and 4 m in length. 6 irrigation treatments were designed including 0, 75, 150, 225, 300 and 375 mm and 6 N fertilization rates were used including 0, 75, 150, 225, 300 and 375 kg/hm2. A total of 27 irrigation-fertilizer coupling treatments were designed. Each treatment had 4 replications. Meteorology data were collected from meteorological station 100 m away from the experimental field. Soil water content was measured after harvest and before sowing of winter wheat. Yield and its component of winter wheat were measured. The results showed that the amount of soil water recharge was significantly affected by the precipitation in summer fallow period (P<0.01). Different irrigation and N fertilizer coupling treatments had great effects on the recharge of soil water in summer fallow period of winter wheat (P<0.05). The coefficient of soil water recharge decreased with the increase of fertilizer application rate and then increased and finally decreased under the irrigation treatments of 0, 225, and 375 mm. At same time soil water recharge coefficient for the treatment of N fertilizer application rate of 225 kg/hm2 was highest. In the same way, it presented a decrease-increase-decrease trend when N fertilizer application changed from 0, 150, to 375 kg/hm2, and the soil water recharge coefficient was highest for the irrigation treatment of 225 mm. The deficit of soil water was exponentially related with soil water recharge, and soil water recharge coefficient was best when the water deficit was 43.68%-52.63%. The soil water recharge coefficient and the contribution rate of soil water recharge coefficient to water consumption of winter wheat were in a relationship of power function. The effect of water supplement to soils was best when the coefficient of soil water recharge was 52.2%-62.4%. The power function was also found between the soil water recharge coefficient and indicators such as yield, spikelet number, spike grain number and thousand seed weight of winter wheat in the following year. Different from the positive relationships between the others and the soil water recharge coefficient, a negative correlation was observed between thousand seed weight and the soil water recharge coefficient. As the soil water recharge coefficient ranged from 25% to 40%, the variation of yield, spikelet number, spike grain number and thousand seed weight was minimal, and this was good for use of precipitation during summer fallow period to increase water use efficiency and yield of winter wheat. The results lay the foundation of soil water and agriculture management, and guide farmers to irrigate with high efficiency for high crop yield.