Biochar improves water and nitrogen use efficiency of cotton under mulched drip irrigation in arid regions

Soil degradation and water scarcity constitute critical impediments to crop production in arid regions. The innovation of efficient resource utilization technology is necessary for agricultural development in arid regions. While biochar application's effects on enhancing soil quality and promoting crop growth have been well documented, the mechanism of biochar application under mulching drip irrigation in cotton field to improve soil hydrothermal environment and then to promote cotton production is unclear. To explore the effects of different amounts of biochar application on soil hydrothermal characteristics, cotton yield, and water-nitrogen utilization efficiency in cotton field under mulched drip irrigation. The experiment encompassed five rates of biochar applications: B1 (20 Mg ha- 1), B2 (40 Mg ha- 1), B3 (60 Mg ha- 1), B4 (80 Mg ha- 1) and CK (0 Mg ha- 1). Compared to CK, the application of biochar could increase soil water storage, soil accumulated active temperature and soil inorganic nitrogen in the top 40 cm of soil. The crop water productivity, crop N uptake, nitrogen partial factor productivity and cotton yield increased by 2.49-13.39 %, 2.66-15.30 %, 3.43-12.00 % and 3.41-11.98 % in treatments with biochar applications, respectively. Besides, the crop N uptake was closely related to cotton yield, which was stemmed from the improvement of soil water storage and soil active accumulated temperature by biochar application, and therefore an increase of the soil inorganic nitrogen content. According to the dualobjective regression analysis of cotton water productivity and cotton N uptake, the optimal biochar application rate was 42.42 Mg ha- 1. The results highlighted that further increasing water and fertilizer use efficiency is feasible under optimized biochar application rate to promote agriculture development in arid regions.