Strategic tillage has no longer term effect on soil microbial communities

Occasional strategic tillage (ST) is an effective tool for managing weeds and crop diseases in no-till farming systems. However, there is a limited understanding of the impacts of ST on soil microbial communities and their catabolic activity, particularly in dryland agriculture. The study aimed to quantify the effect after three years of one-off ST on soil microbial community structure and function in a long-term no-till farming system under varied crop stubble and fertilization management practices. ST significantly affected the abundance of Actinobacteria, Firmicutes, Verrucomicrobia, Basidiomycota and Ascomycota, with marginal effects on microbial richness and diversity, enzyme activities and catabolic function shown by substrate-induced respiration (SIR). Stubble retention regardless tillage and fertilization management mainly increased the abundance of copiotrophs such as Proteobacteria (e.g., Rhizobiales) and Actinobacteria (e.g., Streptomyces and Micromonosporaceae), and affected Ascomycota and Basidiomycota. Among the varied management practices, stubble retention was the main factor that contributed to increased richness and diversity of the soil bacterial and fungal community structure, as well as catabolic utilization of amino acid. Fertilization regardless tillage and stubble management decreased bacterial richness and diversity but had minimal effects on enzyme activity and catabolic function. The variation in bacterial community structure was influenced mainly by soil pH (i.e., 10%), while only a small but significant effect (i.e., < 7%; P = 0.001) was attributed to the experimentally manipulated management practices of tillage and stubble management. In contrast, the variation in fungal community structure was affected by stubble management only. Wheat grain yield ranged between 5 and 5.3 t ha-1, which was not affected by tillage, stubble, or fertilizer management practices. Similarly, these management practices did not influence total soil carbon (C) or nitrogen concentrations. Our findings show that strategic tillage, when used to address specific constraints in no-till systems in dryland agriculture, does not have a long-term effect on total soil C, microbial diversity, or catabolic function.