Combined effects of dry-wet irrigation, redox changes and microbial diversity on soil nutrient bioavailability in the rice field

Sustainable development goals (SDGs) by United Nations are some of the high-priority areas of research and this article established the sustainable agronomic practices converging soil chemistry, crop productivity and soil microbial involvement in nutrient modulation. Alternate wetting-drying (AWD) cultivation with implications 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 irrigation in pre-monsoon and flooded irrigation in monsoon on soil microbiota and the nutrient pool has been studied. Nutrient-less pond water has been used to avoid any external nutrient input from irrigation water to ensure the sole elemental flux within the soil itself. The release of soil nutrients into the soil-aqueous system, influencing microbial populations and modulating the redox status was explored. Results indicated an increase in total concentration 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 with the plant growth and elemental uptake continuum. Crop plant measurements were improved and grain yields were found to be 5.2–6.46% increased under AWD and microbial activity. 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 was 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 some specific groups of soil microbes on macro-micro nutritional availability in soil and enhanced plant quality.