Effect of long-term nutrient managements on biological and biochemical properties of semi-arid tropical Alfisol during maize crop development stages

Understanding the influence of organic or inorganic nutrient management on soil biology and biochemistry during crop growth may help to develop more sustainable fertilization strategies. Hence, the biological variables including soil organic carbon (SOC), microbial biomass carbon (MBC), six cultivable microbial communities, five hydrolytic enzymes activity and soil respiratory indices from a long-term fertility experiment field (>100 years) were assessed at different growth stages of maize. The samples were taken from four long-term treatments viz., control (no fertilization), balanced inorganic fertilizers (IC), organic amendments (OM) and integrated nutrient management (INM, organic manure plus chemical fertilizers) at five different stages of maize cropping (S1, pre-cropping; S2, five days after sowing; S3, vegetative; S4, flowering; S5, after harvesting). Responses of most of the assessed parameters to organic fertilization (OM and INM) were significantly higher than those from inorganically managed and control soils. There was significant difference in SOC due to long-term nutrient managements (OM>INM>IC>control) but not due to growth stages of maize. MBC was also higher in OM and INM compared to IC and control and found significantly different at growth stages of maize. Values of microbial counts and assessed enzyme activities were highest at vegetative stage of maize following a declined trend at later stages. The respiration studies indicate a difference between the responses of substrate induced respiration rate (SIR) and metabolic quotient (qCO2). SIR was more significantly influenced by long-term nutrient managements than crop stages, while qCO2 was by early stage of maize growth (S2) alone. The principal component analysis (PCA) identifies MBC, qCO2, SIR, dehydrogenase, phosphatase and aryl sulphatase and counts of Actinobacteria and diazotrophs as major drivers for the variability among the samples. PCA discriminated OM and INM samples from IC and control and vegetative stage of maize from other stages. The interaction effects of long-term nutrient managements and maize growth stages were found significant to MBC, counts of Actinobacteria and diazotrophs and activities of dehydrogenase, acid phosphatase and aryl sulphatase. However, the resilience of semi-arid tropical soil, independent of long-term nutrient management adoptions, was not affected due to maize growth. The present study thus provides some reliable biological indicators to monitor the semi-arid tropical soils, those influenced by nutrient managements.