Influence of distillery sewage sludge application placement methods on microbial community functions in sorghum rhizosphere: Focus on nitrogen and phosphorus cycling

Abstract

The effect of different fertilization methods using distillery sewage sludge (DSS) on the functional potential of soil microorganisms involved in nutrient cycling is largely unknown. This study used metagenomic sequencing to investigate the effects of two basic DSS application placement methods on soil microbial nitrogen (N) and phosphorus (P) cycling in sorghum rhizosphere soil. The treatments applied were mix powder application (MF), spherical deep application (further classified as vertical (VF) and lateral (LF) placement methods), and no fertilization control (CK). The results showed that microbial diversity is highly correlated with soil AN and Ex-Na. The VF treatment revealed a high abundance of phnA, phnM, appA, and phnJ genes responsible for organic P mineralization. LF treatment significantly increased the abundance of hao and amoA/B/C genes involved in nitrification. MF treatment significantly enhanced the abundance of phnA, phoD, phnM, TC.PIT, and phoB genes, increasing the genetic potential for P cycling. Moreover, the abundance of N denitrification-related genes rose considerably during the MF treatment, increasing the risk of N loss. Network analysis showed that VF and LF treatments reduced the complexity and stability of soil microbial networks while modularity increased. The partial least squares path model demonstrated that N (including available N, ammonium N, and nitrate N), available P, and available potassium (K) directly influence N and P cycling. In contrast, changes in soil organic matter indirectly affect this cycling. This study offers comprehensive insights into the distinct microbial functional potentials associated with various DSS fertilization methods. The findings could potentially impact soil nutrient cycling in agroecosystems, particularly effective solid waste recycling from the distillery industry.