Optimal Drip Fertigation Regimes Improved Soil Micro-Environment, Root Growth and Grain Yield of Spring Maize in Arid Northwest China

Understanding the spatial distributions of soil water, temperature and nutrients as well as their effects on maize growth and grain yield is vital for optimizing drip fertigation regimes. In this study, a 2 year field experiment was conducted on drip-fertigated spring maize with plastic mulching in arid northwestern China in 2015 and 2016. Four irrigation levels were set: as I-60 (60% ETc; ETc is crop evapotranspiration), I-75 (75% ETc), I-90 (90% ETc) and I-105 (105% ETc) in 2015; and as I-60 (60% ETc), I-80 (80% ETc), I-100 (100% ETc) and I-120 (120% ETc) in 2016. Two fertilization rates of N-P2O5-K2O were set: as F-180 (180-90-90) and F-240 (240-120-120). The results showed that the average soil water content in the deeper soil layer (80-120 cm) increased with the increase in irrigation level, and the lowest average soil water content in the 0-80 cm soil layer occurred under I-95 in 2015 and under I-100 in 2016. The irrigation level more significantly influenced the soil temperature at 5 cm than at the other depths. With the decrease in the irrigation level and progression of the growth period, the soil temperature increased. The soil nitrate nitrogen content in the root zone decreased with increasing irrigation level. The largest soil nitrate nitrogen content at the 0-100 cm depth occurred under I-60 in both 2015 and 2016. Significant differences were observed for root length density in the 0-20 cm soil layer at various lateral locations. In deeper (60-100 cm) soil layers, the root length density under I-75 (2015) and I-80 (2016) was greater than at other depths. Grain yield, water use efficiency (WUE) and partial factor productivity (PFP) increased with the increase in irrigation level in 2015, while it increased and then decreased in 2016. I105F180 achieved the maximum grain yield (18.81 t ha(-1)), WUE (3.32 kg m(-3)), and PFP (52.26 kg kg(-1)) in 2015, while I100F180 achieved the maximum grain yield (20.51 t ha(-1)), WUE (3.99 kg m(-3)), and PFP (57.02 kg kg(-1)) in 2016. The optimal drip fertigation regimes for spring maize in arid northwest China were recommended as 90-100% ETc and 180-90-90 (N-P2O5-K2O) kg hm(-2).