Soil Nutrient Retention and Yield Effect of Nitrogen, Phosphorus Synergists on Wheat/Maize Rotation in Brown Soil

The aim was to improve the fertilizer utilization efficiency and alleviate environmental pollution risk under a wheat-maize rotation system. Here, the combinations of different nitrogen stabilizers and phosphorus activators were used to reduce nitrogen loss and phosphorus fixation in the field experiment. Compared to the control, the combination of 1.5%HQ + 0.5%DMPP + biochar showed the most significant effect on the retention of alkali-hydrolysable nitrogen (Nah), the highest with an increase of 22.6% at the 0 similar to 20 cm layer soil; and the combination of 1.5%HQ + 3.5%DCD + CMFs (compound microbial fertilizers) showed the most significant effect on the maintenance of available phosphorus (Pa), with the highest increase of 41.3%. N, P synergists combined with a basal fertilizer could effectively slow down the transformation from NH4+, NHO3- to and keep NH4+ at an increase of 7.38%similar to 19.6%. Moreover, the N, P synergists could efficiently lock the available nutrients around the roots, preventing the migration of NO3-, NH4+, Nah, and Pa to the deeper layers. Especially for NO3-, the total accumulation at 0 similar to 60 cm decreased by 32.1%, and the activation of Pa was mainly concentrated at 0 similar to 40 cm. Under the same nutrient inputs, the combination of 0.3%NBPT + 0.5%DMPP + CMFs obtained the highest wheat yield. The combination of 1.5%HQ + 0.5%DMPP+ biochar gained the highest maize yield. Overall, the application of N, P synergists could increase the effective duration of Nah, Pa, and NH4+ in the surface soil, and reduce the accumulation of NO3- in the 0 similar to 60 cm soil layer. The capacity of holding and keeping nutrients from leaching rose obviously; simultaneously, the assimilative capacity of crops for nitrogen and phosphorus increased distinctly, which could lower the eutrophia risks from nitrogen and phosphorus.