Arnab Majumdar, Munish Kumar Upadhyay, Pradeep Kumar Dubey, Biswajit Giri, Ashish Kumar Srivastava, Sudhakar Srivastava

Alternate wetting-drying (AWD) cultivation with implication on soil microbiome, nutritional dynamics and rice yield during pre-monsoon (boro) and monsoon (aman) season are not well studied. In the present 4-year field study the impact of AWD (in pre-monsoon season) is compared with conventional mode of irrigation (i.e. flooded field in monsoon season). The release of soil nutrients into the soil-aqueous system, influencing microbial populations and modulating the redox status were explored. Results indicated an increase in total content as well as bioavailability of selected nutritional elements (N, P, K, Fe, Ca, Mg, Cu and Zn) by 16-54% in the pre-monsoon cultivation relative to monsoon cultivation. Three plant growth phases (developing, milking and harvest) were considered to check the nutrient modulations in soil and plant tissues along the continuum plant growth and elemental uptake. Krona charts, relative abundance, rarefaction curve and multivariate analysis of metagenomics data showed that the pre-monsoon soil was more enriched and maintained a balance between soil pH and microbial biomass than the monsoon soil. Microbial community diversity associated with plant growth phases also found to be different depending on the seasonal alterations. Bacillus sp., Acidothiobacillus sp., Pseudomonas sp., Rhizobium sp., Burkholderia sp. were predominant in pre-monsoon soil releasing pulses of N, P, K, Ca and Mg whereas Verrucomicrobia was found to be dominant in monsoon soil where Fe was released. This study is a first of its kind that showed the combined effect of season and soil microbes on macro-micro nutritional availability in soil and enhanced plant quality.
Keywords: Soil quality; Metagenomics; Nutrient availability; Pre-monsoon irrigation; Resource conservation; Soil microbiome