Integrated application of inorganic fertilizer with fulvic acid for improving soil nutrient supply and nutrient use efficiency of winter wheat in a salt-affected soil

Establishing better nitrogen (N) management strategies is of great significance for sustaining crop production and reducing environmental pollution. However, there is limited knowledge about N fertilizer management practices with soil nutrient supply, N leaching, crop productivity and nutrient use efficiency (NUE) reaching the desired level simultaneously. In this study, pot experiment was conducted to evaluate the effects of N fertilizer and in combination with fulvic acid (FA) on NUE and nutrient supply in a moderate-salinized soil (with total salt content 3.30 g kg- 1 and EC1:5 1.18 dS m-1). Ten treatments were included: treatment without any addition (CK); 100%, 85% and 70% of the conventional inorganic N fertilizer addition rate (100% CF, 85% CF and 70% CF); 100% CF, 85% CF and 70% CF combined with 75 kg ha-1 FA (100% CF + F1, 85% CF + F1, and 70% CF + F1), respectively; and 100% CF, 85% CF and 70% CF combined with 150 kg ha- 1 FA (100% CF + F2, 85% CF + F2, and 70% CF + F2), respectively. In order to further investigate the effects of combining N fertilizer and FA applications on soil N leaching losses, part of the fertilizer management practices were selected to conduct a soil leaching experiment. The results demonstrated that the Olsen-P for the upper 20 cm of soil was significantly affected by N fertilization (P <= 0.01). In the treatments with inorganic fertilization alone, the concentration of soil mineral N at 0-10 cm soil depth decreased with decreasing level of fertilizer N, while Olsen-P content and alkaline phosphatase activity decreased with increasing N fertilizer application rate. The application of FA significantly increased alkaline phosphatase activity. Overall, the total mineral N leaching losses increased exponentially with increasing annual fertilizer N application rates, while the addition of FA decreased the total mineral N leaching factor (TLFN). Furthermore, the results of multiple regression analysis revealed that wheat grain yield, plant P uptake, plant N uptake, harvest index of applied fertilizer N (HIN), partial factor productivity of applied fertilizer P (PFPP), recovery efficiency of P (REP) and recovery efficiency of N (REN) reached >= 85% of their maximum concurrently, when the application amounts of N fertilizer and FA varied from 300 to 370 kg ha- 1 and from 164 to 250 kg ha- 1, respectively. These results of this study provide a basis for appropriate nitrogen (N) management in salt-affected soils and for the improvement of the sustainability of agricultural development in China.