The Effects Mechanisms of Polymeric Materials Combined with Nitrogen Fertilizer on Soil Biome Features and Microbial Community Metabolism of Drip-Irrigated Wheat in Arid Areas

Polymers can be used as soil water-retention agents to slow down fertilizer nutrient release and improve soil properties. However, the mechanism of combined application of polymer and nitrogen fertilizer influencing soil biocommunity characteristics and nitrogen transformation is still unclear. In this study, the polymer PPM with water retention and slow-release functions was combined with nitrogen fertilizer (N100 treatment: 300 kg/hm2 of nitrogen fertilizer (traditional nitrogen application rate); PN100 treatment: PPM + 300 kg/hm2 of nitrogen fertilizer; PN80 treatment: PPM + 240 kg/hm2 of nitrogen fertilizer) to investigate soil biodiversity, enzyme activities, and metabolomics. The objective was to clarify the effects of combined application of polymer and nitrogen fertilizer on soil characteristics, biocommunity structure, and metabolites in drip-irrigated wheat fields in arid areas. The results showed that under the application of PPM, the contents of soil total nitrogen (TN), alkali hydrolyzable nitrogen (ANS), nitrate nitrogen, organic carbon (SOC), and microbial biomass nitrogen (MBN) increased with the decrease of nitrogen application rate, while soil bulk density, pH, and EC (electrical conductivity) showed an opposite change. The Chao 1 index of soil bacterial and nematode communities of the PN80 treatment increased by 30.63% and 10.68%, respectively, and the Shannon index increased by 2.72% and 2.64%, respectively, compared with those of N100 treatment, but there was no difference in the Pielo e index. The results of RDA (redundancy analysis) and co-occurrence network showed that combined application of PPM and nitrogen fertilizer improved soil physicochemical properties, and soil ammonium nitrogen, TN, SOC, and MBN contents were the key factors affecting the distribution of soil bacterial communities. In addition, in the short term, the addition of PPM affected the structure and composition of soil bacterial and nematode communities. Especially, the relative abundances of omnivorous (Aporcelaimellus) and bacterivorous (Prismatolaimus) nematodes increased significantly compared with those of N100 treatment, actively responding to changes in the soil environment. This regulated the soil microbial communities and metabolites, thereby promoting soil nitrogen transformation. This study will provide a scientific basis for nitrogen reduction, farmland environment protection, and agricultural production efficiency improvement in drip-irrigated wheat planting in arid regions.