Evaluating Water and Nitrogen Use Efficiencies At Different Crop Systems Using Crop-Soil System Processes Model in North China.

The objectives of this study were to compare water and nitrogen use efficiencies (WUE, NUE) and their environmental impacts in the North China Plain (NCP) under three different cropping systems: (i) traditional winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system under farmers' practice (FP) and reduced water and fertilizer input (RI), (ii) three harvests in two years (HT): spring maize monoculture system followed by winter wheat-summer maize rotation system under RI treatment and (iii) continuous spring maize monoculture system (CS) under RI treatment. For the FP treatment, the total amounts of irrigation and fertilizer in two years were 820 mm and 1100 kg N ha^-1, respectively, while they are 720 mm and 540 kg N ha^-1 for RI treatment based on monitoring soil water content and N_min in traditional rotation system. After a Water and Nitrogen Management Model (WNMM) was calibrated and validated, the yields, amounts of drainage, N leaching, WUE and NUE for two treatments were all obtained. For traditional rotation system, the results showed that amounts of drainage in two years were 253 mm and 214 mm for FP and RI, respectively,. Amounts of N leaching were 407 and 68 kg N ha^-1 for FP and RI, respectively. The yield, WUE and NUE under the RI treatment were all higher than those under the FP treatment. For three rotation systems, the irrigation amounts were 720, 545 and 265 mm for RI, HT and CS, respectively, While the amounts of fertilizer were 540, 335 and 165 kg N ha^-1,, respectively. Analyzing from the aspect of the drainage, N leaching and WUE and NUE of agricultural crops, CS or HT showed a high potential for water-saving, fertilizer-saving and high use efficiencies. The yield of spring maize could be higher with improving water and nitrogen management, better cultivars and other agricultural management techniques. The yield of spring maize would increased by over 10% when sowing date was delayed to mid or end of May in this region. Once the yield of spring maize reached to a higher level, HT or CS would be water-saving, fertilizer-saving high-use efficiency and high-yield cropping systems, and these cropping systems would be very useful for improving WUE and NUE of agricultural crops and developing a sustainable agriculture in the NCP. These indicated that the water and N management based on the requirement of crops and an improved N_min method was an effective way to save water and N input and increase the WUE and NUE of the crops while the yield was guaranteed.