Soil carbon-nutrient cycling, energetics, and carbon footprint in calcareous soils with adoption of long-term conservation tillage practices and cropping systems diversification.

Calcareous soils, comprising vast areas in northern and eastern parts of India, are characterized by low soil organic carbon (SOC) with high free CaCO3 that results in low nutrient bioavailability with poor soil structure. Improvement of this soil can be achieved with conservation tillage with residue retention coupled with diversification of cropping system including legumes, and oilseeds in the system. Concerning all these, a long-term experiment was carried out in the calcareous soils having low organic carbon and high free CaCO3 (∼33 %) with varied tillage practices, viz. permanent bed with residue (PB), zero tillage with residue (ZT), and conventional tillage without residue (CT); and cropping systems viz. maize-wheat-greengram (MWGg), rice-maize (RM), and maize-mustard-greengram (MMuGg) during 2015-2021. From this study, it was observed that PB and ZT resulted in ∼25-30 % increment in SOC compared to the initial SOC, while CT showed a 4 % decrease in the SOC. Conservation tillage practices also resulted in better soil aggregation and favourable bulk density of the soil. Furthermore, PB and ZT practice exhibited 10-13 %; 15-18 %; 11-15 %; 40-60 %, 20-36 %, and 23-45 % increments in the soil available N, P, K, soil microbial biomass carbon, dehydrogenase activity, and urease activity, respectively over those under CT. Crop diversification with the inclusion of legume and oilseed crops (MMuGg, and MWGg) over cereal-dominated RM systems resulted in better soil health. Maize equivalent yield and energy use efficiency (%) were also found to be the maximum under PB, and ZT, in combination with the MMuGg system. ZT and PB also reduced the carbon footprint by 465 and 822 %, respectively over CT by elevating SOC sequestration. Hence, conservation tillage practices with residue retention coupled with diversification in maize-based cropping systems with mustard and greengram can improve soil health, system productivity, and energetics, and reduce the carbon footprint in calcareous soils.

Microbial biosurfactants: Multifarious applications in sustainable agriculture.

Agriculture in the 21st century faces grave challenges to meet the unprecedented food demand of the burgeoning population as well as reduce the ecological footprint for achieving sustainable development goals. The extensive use of harsh synthetic surfactants in pesticides and the agrochemical industry has substantial adverse impacts on the soil and environment due to their toxic and non-biodegradable nature. Biosurfactants derived from plant, animal, and microbial sources can be an eco-friendly alternative to chemical surfactants. Microbes producing biosurfactants play a noteworthy role in biofilm formation, plant pathogen elimination, biodegradation, bioremediation, improving nutrient bioavailability, and can thrive well under stressful environments. Microbial biosurfactants are well suited for heavy metal and organic contaminants remediation in agricultural soil due to their low toxicity, high activity at fluctuating temperatures, biodegradability, and stability over a wide array of environmental conditions. This green technology will improve the agricultural soil quality by increasing the soil flushing efficiency, mobilization, and solubilization of nutrients by forming metal-biosurfactant complexes, and through the dissemination of complex nutrients. Such characteristics help it to play a pivotal role in environmental sustainability in the foreseeable future, which is required to increase the viability of biosurfactants for extensive commercial uses, making them accessible, affordable, and economically sustainable.