Induced decline of alkali and sodium content in the rhizosphere by applying ammonium containing fertilization can increase the adaptation and yield of crops to salt-affected soil

It is of great significance to improve the green productivity of saline-alkali soil by changing the cultivation mode to stimulate the potential of crop resistance to salt and alkali, and achieve the goal of increasing the yield and efficiency of crops by planting suitable soil. In this experiment, the winter wheat-summer maize rotation system in coastal saline-alkali land was used as the research object. Using the field positioning experiment, the treatment includes the following six: AS0 (100% urea, phosphorus fertilizer reduction), AS50 (50% urea +50% ammonium sulfate, phosphorus fertilizer reduction), AS75 (25% urea +75% ammonium sulfate, phosphorus fertilizer reduction), AS50 (100% ammonium sulfate, phosphorus fertilizer reduction), FP (farmers over fertilization, 100% urea, control 1) and P0 (no phosphorus fertilizer, 100% urea, control 2). The changes in yield, nutrient uptake, nitrogen and phosphorus fertilizer utilization efficiency, and rhizosphere soil pH, salinity and sodium adsorption ratio (SAR) of winter wheat and summer maize were analyzed under different ammonium sulfate replacement urea ratio treatments. The results of the 2-year field experiment showed that the yields of wheat and maize treated with P0 were the lowest, indicating that the soil lacked phosphorus. There was no significant difference in yield between all phosphorus reduction treatments and FP treatment. Under the condition of iso-nitrogen and phosphorus, the AS50 treatment resulted in an average yield increase of 5.4% for winter wheat and 1.5% for summer maize compared to AS0. Compared with AS0 treatment, increased application of ammonium sulfate (AS50, AS75, AS100) reduced the pH of wheat rhizosphere soil by 0.08 to 0.24 units, and the pH of corn rhizosphere soil by 0.06 to 0.35 units. With the increase of ammonium sulfate ratio, the content of available phosphorus in rhizosphere soil increased first and then decreased, and the content of available phosphorus in AS50 treatment was the highest. The content of Ca²⁺, Na⁺ and SAR in rhizosphere soil decreased. Compared with FP treatment, rhizosphere pH, SAR and Na⁺ contents of AS50 and AS75 treatment were significantly reduced, and nitrogen and phosphorus fertilizer utilization efficiency were significantly improved. Moreover, the treatment effect of maize season was more significant than that of wheat season. In coastal saline-alkali cultivated lands, compared to the FP treatment, substituting 50% of urea with ammonium sulfate under reduced phosphorus application can promote the reduction of SAR and Na⁺ content and the increase of available phosphorus and Ca²⁺ content by inducing a decrease in rhizosphere pH. This created a more suitable rhizosphere environment with lower salt, lower alkali, and higher nutrient content for crops, thereby enhancing yield and fertilizer utilization efficiency. Based on the above understanding, the technical principle of adding ammonium, reducing alkali, mobilizing phosphorus and increasing calcium to induce the separation of fertilizer and salt distribution at the root-soil interface was put forward to achieve the increase of crop yield and efficiency in light to medium saline-alkali soil.