Lessons from Long-term Nutrient Management Adoptions in Semi-arid Tropical Alfisol

Understanding the consequences of adoption of long-term nutrient managements on the fluctuation of soil biological variables is of greater importance in relation to nutrient supplying capacity of the ecosystem and crop requirement. The knowledge of linkage between nutrient management strategies and the soil microbiome and biochemical processes would be useful for soil health sustainability. The results from comprehensive study made on a field experiment comparing the long-term (more than 100 years) effects of organic manures and inorganic chemical fertilizers on soil biological and biochemical properties are reviewed. The soils adopted with three nutrient managements viz., no fertilization (control), inorganic chemical fertilizers (IC) and organic amendments (OM) obtained from long-term fertilizer experiment were assessed for physical, chemical, microbiological and biochemical properties in three successive years. The response of most of the assessed soil variables including soil organic carbon, microbial biomass carbon, humic and fulvic acid fractions, population of different functional bacterial communities, eubacterial community diversity and enzymes’ activity to long-term organic nutrient management was significantly higher than those from inorganic fertilization and control (OM > IC = control). The biological properties and enzymes activity of the soil was unaffected due to long-term use of inorganic chemical fertilizers, as those were on par with control. The culture-independent molecular approaches also revealed that the organic manures encourage the overall biodiversity of eubacteria and to be specific, favour to some of the eubacterial phyla viz., Acidobacteria, Actinobacteria. The functionality of total soil microbiome assessed through respiration indices implies that the metabolic quotient was unaffected due to nutrient management, while OM had highest substrate induced respiration rate compared to IC and control. The principal component analysis of assessed soil variables clearly discriminated the OM from IC and control. The evidence from these observations shows that addition of organic manures is vital to enhance the abundance, diversity and functionality of microbiome of soil and thereby the fertility sustainability. However, it is also observed in our investigations that adoption of balanced inorganic chemical fertilization, which provides instant nutrients to the crop plants, had no harm to the microbial diversity and functionality as well as the soil processes including respiration and enzymes functioning.