Long Term Fertilization on Soil Nutrient Dynamics, Soil Quality and Soil Bacterial Community Structure in an Inceptisol Under Semi-arid Tropics of Finger Millet (Eleusine coracana) - Maize (Zea Mays) Cropping Sequence

The main aim of this study is to assess the long-term effect of continuous fertilizer and manure addition, as well as intensive cropping, on nutrient availability, major nutrient forms, soil quality, and the composition of soil eubacterial communities over a span of five decades.

Nutrient dynamics involving nitrogen (N), phosphorus (P), and sulphur (S) were analysed using standard procedures. The eubacterial community structure was investigated through Illumina next-generation sequencing with HiSeq 2500 PE250, focusing on the V4 region of bacterial genes. Principal component analysis was employed as a suitable method for identifying specific key indicators for assessing soil health and sustainability in long-term fertilizer experiments.

Application of NPK fertiliser along with 10 t ha^− 1 of FYM led to improvements in nutrient fractions of N, P, and S, as well as soil enzyme activities such as urease (URE), acid phosphatase (ACP), alkaline phosphatase (ALP), dehydrogenase (DHA), and aryl sulphatase (AS). It also enhanced nutrient availability and soil organic carbon (SOC) dynamics, which includes SOC content, SOC stock, SOC sequestration, soil microbial biomass carbon (SMBC), and soil microbial biomass nitrogen (SMBN). These improvements were observed in a sandy clay loam Inceptisol over a five-decade period. According to Illumina sequencing of the 16 S rRNA gene, the relative abundance of various bacterial domains such as Proteobacteria, Actinobacteria, Firmicutes, Gemmatimonadetes, Acidobacteria, Bacteroidetes, and Verrucomicrobiae changed based on the different nutrient management techniques.

Through the use of principal component analysis (PCA), specific critical indicators for soil health were identified, with key limiting parameters including soil fractions of P, S, zinc (Zn), and the enzymes like URE and DHA activities, as well as SOC and SMBN. The composition of the eubacterial community varied based on different nutrient management practices, with a more balanced bacterial community observed in NPK + FYM plots compared to mineral-fertilized plots. In conclusion, the study suggests that integrated nutrient management practices can significantly improve sustainability and maintain soil health, as compared to relying solely on chemical fertilizer application, even over a period of five decades of intensive cultivation.