Effect of biofertilizer addition on soil physicochemical properties, biological properties, and cotton yield under water irrigation with different salinity levels in Xinjiang, China

Saline water irrigation is extensively employed in many arid regions due to its capacity to effectively alleviate the scarcity of freshwater resources. However, this practice can result in an escalation of soil salinity and a decline in crop yield. Hence, it is necessary to explore measures to improve edaphic properties during saline water irrigation. This study aimed to explore the impact of biofertilizer application on soil physicochemical and biological characteristics, nitrogen use efficiency, and yield under irrigated conditions with water of different salinities and to establish the relationship between them. A two-year field experiment was conducted in 2021 and 2022 in film-mulched drip-irrigated cotton fields. Three types of irrigation water with different salinity levels of 0.48–1 g L−1 (W1, fresh water), 3 g L−1 (W2, brackish water), and 7 g L−1 (W3, salt water) and two fertilizer types of chemical fertilizer (F1) and chemical fertilizer+biofertilizer (F2) were assigned. Nitrogen, phosphorus, and potassium applications were maintained at the same amount for all treatments. The addition of biofertilizers resulted in a significant increase in lint cotton yield by 6.45–11.79 % (W1F2) and 6.69–15.51 % (W2F2) in two years under fresh and brackish water irrigation conditions when compared to conventional fertilization. Partial least squares path analysis revealed that the amplified cotton yield primarily stemmed from heightened soil nutrient effectiveness, increased soil microbial biomass, and enhanced nitrogen utilization efficiency (aNUE) facilitated by the application of biofertilizers. The addition of biofertilizers significantly lowered the soil specific gravity, improved water-salt distribution, reduced plant Na+ uptake, and alleviated the impact of salt stress under freshwater and brackish water irrigation, in contrast to conventional fertilization. Furthermore, the application of biofertilizers markedly elevated urease and invertase activities, increased soil microbial biomass (C and N), promoted nutrient uptake by crops, and increased nitrogen accumulation by plants. However, the efficacy of biofertilizer application was found to be less pronounced in saltwater irrigation. Biofertilizers can effectively improve the soil conditions under fresh and brackish water irrigation, promote nutrient absorption in crops, and significantly increase aNUE while simultaneously reducing internal nitrogen use efficiency (iNUE). An optimal combination of bio-fertilizers and chemical fertilizers can be employed to increase crop yields while effectively minimizing the application of nitrogen fertilizer under fresh and brackish water irrigation conditions.