Abstract: 【Objective】To explore the effects of different fertilizer combined applications on soil nutrients,photosynthetic physiological indexes and yield formation of foxtail millet in the loess arid farming region of Shaanxi.【Methods】Foxtail millet variety Changsheng 07 was used as experimental material,and random block design was adopted,N 45 kg/hm²（CK）,N 60 kg/hm²+P₂O₅ 30 kg/hm²（G1）,N 90 kg/hm²+P₂O₅ 45 kg/hm²（G2）,N 60 kg/kg/hm²+P₂O₅ 40 kg/hm²+organic fertilizer 2 000 kg/hm²（G3）,N 60 kg/hm²+P₂O₅ 40 kg/hm²+microbial fertilizer 5 kg/hm²（G4） 5 fertilizer treatments were set up to carry out field experiments,the differences of soil nutrients and root morphology,photosynthetic physiological indexes,yield and its components,water use efficiency of foxtail millet under different treatments were analyzed.【Results】In foxtail millet filling stage,G3 treatment had the highest soil organic matter content（5.67 g/kg）,G2 treatment had the highest soil available phosphorus content（11.93 mg/kg）,G4 treatment had the highest soil available potassium content and hydrolyzed nitrogen content（81.00 and 20.07 mg/kg,respectively）. In foxtail millet maturity stage,soil organic matter content in G4 treatment was the highest（6.05 g/kg）,soil available phosphorus content in G2 treatment was the highest（13.47 mg/kg）,and soil hydrolyzed nitrogen content in G3 treatment was the highest（19.40 mg/kg）. Compared with CK,all treatments significantly improved the root length and root surface area of foxtail millet（P<0.05）,G3 treatment showed a significantly increased by 49.25% and 64.28% in root length and root surface area compared with CK,respectively（P<0.05）. In foxtail millet heading stage,the net photosynthetic rate in G2 treatment was significantly increased by 42.67% compared with CK（P<0.05）,and the stomatal conductance,transpiration rate and SPAD value in G1 treatment were increased by 81.00%,57.82% and 10.72% compared with CK,respectively;in foxtail millet filling stage,the net photosynthetic rate of G2 treatment compared with CK was increased by 9.81%,stomatal conductance and transpiration rate of G4 treatment compared with CK were decreased by 19.90% and 23.58%,respectively,and SPAD value of G1 treatment compared with CK was significantly increased by 22.93%（P<0.05）. The weight per ear,ear length and grain weight per ear of G1 treatment were increased by 43.26%,7.76% and 57.33% compared with CK;the ear width of G2 treatment increased by 8.61% compared with CK;the 1 000-grain weight of G4 treatment was significantly increased by 67.84% compared with CK（P<0.05）;foxtail millet yield and water use efficiency of G3 treatment were significantly increased by 123.63% and 123.51% compared with CK（P<0.05）,respectively,followed by G4 treatment.【Conclusion】Reasonable combined application of N and P fertilizer in the loess arid farming region in Shaanxi can effectively improve the soil nutrient structure,regulate the root morphology development and function of foxtail millet,promote the photosynthetic production capacity of foxtail millet,on this basis,the addition of organic fertilizer and microbial fertilizer can stimulate the potential increase of foxtail millet yield and water use efficiency.

Key words: Loess arid farming region, Foxtail millet, Fertilizer combined application, Soil nutrient, Photosynthetic physiological index, Yield, Water use efficiency