Winter Wheat Yield Gaps Across the Loess Plateau of China

The Loess Plateau is among the major winter wheat (Triticum aestivum L.) production areas of China. However, wheat production is uncertain across the Loess Plateau, and its potential for yield improvement remains unknown. In the present study, we divided winter wheat growing areas on the Loess Plateau into four climatic zones: arid (zone I), semi-arid (zone II), semi-humid (zone III), and humid (zone IV). Then, we used the validated Agricultural Production Systems Simulator (APSIM) to model Y (potential yield) and attainable yield (water-limited yield, Y; nitrogen-limited yield, Y) of winter wheat on the Loess Plateau from 1961 to 2016. The simulated means for weighted Y, Y, and Y were 8.87, 6.49, and 5.42 t ha, respectively. Y reached only 57% of Y, which represents the amount of room available for yield improvement. Across the Loess Plateau, the yield gap caused by water limited (YGw) and nitrogen restricted (YGn) were 27% and 39% of potential wheat production. The difference between YGw (3.54 t ha) and YGn (3.87 t ha) was not significant in the semi-arid climate (zone II), due to low precipitation rates. Compared with irrigation, nitrogen deficiency was the key factor causing the winter wheat yield gap. However, the yield gap caused by nitrogen restriction varies regionally. Irrigation in arid (zone I) was more important than in the other climates, whereas these climate regions required nitrogen more pressing. Areas with a large potential for increased winter wheat yield on the Loess Plateau were mainly distributed in the semi-arid climate (zone II).