Growth, yield, and nitrogen use in the wheat/maize intercropping system in an arid region of northwestern China

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Relay intercropping of spring wheat and maize is practiced on a large scale in northern China. In order to provide information on productivity and nitrogen use for spring wheat/maize intercropping, a two-year experiment under three N levels and three cropping systems (monocultured wheat, monocultured maize, and intercropped wheat and maize) was carried out in the Hetao Irrigation District of the Inner Mongolia Autonomous Region, to quantify and characterize the growth and yield of the wheat and maize and determine the uptake and use efficiency of nitrogen in two crops.The land equivalent ratio (LER) of the wheat/maize intercropping system ranged from 1.01 to 1.19, and thus land use efficiency was significantly enhanced by this intercropping system. The dry-matter yield and LAI (leaf area index) of wheat were higher in border rows than in inner rows and monocultured rows, indicating an effect of border rows in the intercropping system. The LAI was considerably lower for the intercropped than the monocultured maize, indicating that intercropping limited the vegetative growth of maize.The grain yield and nitrogen uptake of both wheat and maize in two cropping systems were significantly improved with increasing amounts of N application. The LER of intercropping system tended to increase at higher N levels.The patterns of maize growth in the monocultures and intercrops were characterized by fitting expolinear growth equations to periodic harvest data. Fitted parameters indicated a growth delay in the intercropped maize ranging from 2.39 to 8.24d relative to the maize monoculture. The growth delays were shortest at the moderate N rate among three N levels (2.39d in 2012 and 2.57d in 2013). This result could be interpreted in terms of the competitive effect of wheat during the seedling phase of maize, which was weakest at the moderate N rate, causing a comparatively short growth delay. The estimated growth rate during the linear growth phase was highest in the intercrop in the high N treatment (417.5kgha−1d−1 in 2012 and 376.7kgha−1d−1 in 2013).The physiological nitrogen use efficiency (IE) was more favorable for monocultured wheat and intercropped maize and decreased as N rates increased. The efficiency of the use of N for the entire system was assessed by comparing the relative nitrogen yield total to the relative yield total. The relative nitrogen yield total ranged from 1.06 to 1.23, while the relative yield total ranged from 1.01 to 1.19, indicating that the intercrop used more nitrogen per unit production than did the monocultures.