Long-term combined organic and inorganic fertilization enhances soil quality and crop yield by regulating bacterial diversity and soil physicochemical properties

Abstract

Introduction Soil microorganisms are widely recognized as a key indicator of soil quality. However, how the application of organic fertilizers drives soil quality and crop yield through microbial pathways is still unclear. Methods A long-term field experiment conducted on the Loess Plateau evaluated the effects of different fertilization treatments on soil properties, microbial communities, and crop yields. The treatment groups included no fertilization (CK), inorganic nitrogen (N), inorganic phosphorus (P), organic fertilizer alone (M), nitrogen-phosphorus compound fertilizer (NP), and a combination of organic fertilizer and nitrogen-phosphorus compound fertilizer (MNP). Results Both MNP and M treatments significantly increased the soil quality index (SQI) and grain yield, with the MNP treatment showing a more pronounced effect than the M treatment. SOC and TN were identified as the main factors influencing SQI. Compared with CK, the MNP treatment increased wheat and maize yields by 208.04 and 103.19%, respectively. Under the MNP treatment, the relative abundance of dominant bacterial phyla and genera increased, among which the increases in Pseudomonadota and Chthoniobacter were significantly correlated with soil properties. Furthermore, the MNP treatment also led to an increase in bacterial alpha diversity. Regression analysis indicated that bacterial alpha diversity was positively correlated with the contents of SOC, TN, MBN, MBC, and NH₄+-N, but negatively correlated with soil pH. Both bacterial community composition and diversity positively contributed positively to SQI. The main factors driving the increase in bacterial alpha diversity included pH, WFPS, NO₃−-N, Olsen-P, and NH₄+-N. Discussion In conclusion, the long-term combined application of organic and inorganic fertilizers can improve soil quality, enhance bacterial diversity, and maintain crop yields.