Cleaner production technologies for the amelioration of soil health, biomass and secondary metabolites in Ocimum basilicum L. under Indian Western Himalaya

Abstract

Ocimum basilicum L. and its derived products are primarily consumed by humans; hence, agrochemical use seems inappropriate for its cultivation. However, farmers are accustomed to using rampant inorganic fertilizers to augment crop productivity, which has unintendedly engendered severe environmental perturbations. Concomitantly, farmers will soon have to confront the challenges of growing crops under suboptimal conditions driven by global climate change. Consequently, to develop a clean, sustainable, and resilient production technology, field experiments spanning over two years (2020 and 2021) were conducted, comprising three biostimulants, viz., vermicompost (0, 4, and 8 Mg ha−1), biofertilizer (uninoculated and inoculated), and liquid seaweed extract (without and at 7 ml L−1) in the Indian western Himalaya for the first time. Soil health indicators, leaf photosynthetic pigments, gaseous exchange, mineral contents, essential oil (EO) quantity, and composition were evaluated. Soil microbial respiration (SMR), microbial biomass carbon (MBC), organic carbon (OC), dehydrogenase (DHA), alkaline phosphatase (ALP), and β-glucosidase activities were increased by 36.23, 83.98, 30.61, 42.69, 34.00, and 40.57%, respectively, when compared with the initial soil status. The net photosynthetic rate (Pn) was significantly increased with the highest (8 Mg ha−1) and moderate (4 Mg ha−1) vermicompost dosages by 13.96% and 4.56%, respectively, as compared with the unfertilized control (0 Mg ha−1). Likewise, the biofertilizer and seaweed extract also enhanced Pn by 15.09% and 10.09%, respectively. The crop’s key EO constituents, viz., methyl chavicol and linalool, were significantly improved with the highest and moderate vermicompost rates of 2.71, 9.85%, and 1.18, 5.03%, respectively. Similarly, biofertilization and seaweed application also boosted methyl chavicol and linalool by 3.29, 8.67%, and 1.93, 3.66%, respectively. In both years, significantly higher herbage (8.86 and 11.25 Mg ha−1) and EO yield (113.78 and 154.87 kg ha−1) were recorded with a congregate treatment of the highest vermicompost dose, biofertilizer, and liquid seaweed extract. In conclusion, the integrated use of biostimulants having complementary properties can sustainably maximize the quantity and quality of O. basilicum and concomitantly ameliorate soil health. This study can inspire scientific communities and industries to develop second-generation biostimulant products, delivering better sustainability and resilience for a renaissance in agriculture.

Comparative Genomics and Physiological Investigations Supported Multifaceted Plant Growth-Promoting Activities in Two Hypericum perforatum L.-Associated Plant Growth-Promoting Rhizobacteria for Microbe-Assisted Cultivation

“…The earthen pots (diameter, 15 cm; capacity, 3 kg) were filled with the sterile potting mixture and then irrigated with sterile distilled water (SDW) for a week before the transplantation of seedlings. Isolates were grown in a sterile nutrient broth medium in an incubator shaker (20 ± 1°C; 120 rpm) for 48 to 72 h. Afterward, the cultures were centrifuged at 6000 × g to settle the cells, followed by resuspension in sterile normal saline (0.9%) by keeping the final concentration of cells at about 1 × 10 8 CFU mL −1 (optical density at 600 nm [OD 600 ], 1) ( 76 ).…”

“…After transplantation, 10 mL of the respective bacterial inoculum was poured into every pot close to the roots, whereas for the mock-inoculated pots, 10 mL SDW was used. Additionally, a second inoculation (booster) was delivered 15 days after the first inoculation by pouring another 10 mL of corresponding bacterial inoculums (1 × 10 8 CFU mL −1 ) in the vicinity of roots to ensure PGPR colonization in the newly emerging roots and to fasten bacterial growth ( 76 ). Watering was suspended for 24 h before and after inoculation procedures to preclude washing.…”

“…The photosynthetic pigments, viz. , Chl a and Chl b , including carotenoids, were estimated as described earlier by Raj et al ( 76 ) at 90 days after booster treatment by collecting fully expended healthy leaves. Additionally, the fluorescence characteristics of chlorophyll (Chl) were evaluated in vivo with a portable pulse amplitude modulation fluorometer (Junior PAM, Walz, Effeltrich, Germany) using Wincontrol-3 software.…”

“…A light dependence curve was established with the application of a series of nine saturating pulses, with rising actinic irradiance ranging from 0 to 820 μmol photons m −2 s −1 to determine the electron transport rate (ETR = ΦPSII × PAR × 0.5 × leaf absorptivity coefficient ([0.85]), photochemical quenching (qP = [F m′ − F s ]/]F m′ − F 0′ ]), and PSII operating efficiency (ΦPSII = [F m′ − F s′ ]/F m′ ) ( 60 ). Additionally, the leaf gaseous exchange-related attributes were recorded with a portable infrared gas analyzer (IRGA) having a portable leaf chamber of 2 cm by 3 cm (6 cm 2 ) and a red-blue LED light source (LICOR-6400 XT, LICOR Biosciences, Lincoln, NE, USA) ( 76 ). Three individual plants, the same used for Chl fluorescence, were selected per treatment for the measurement.…”