Physiological, biochemical and soil microbial responses of green gram (Vigna radiata L.) to foliar nutrition of nano- fertilizers

A field experiment was conducted at Tamil Nadu Agricultural University, Coimbatore, during the summer of 2024 to determine the physiological, biochemical, and microbial responses of green gram to foliar nutrition of nano-fertilizers. The experiment was carried out in black heavy clay soil (Vertisol). Treatments included recommended doses of fertilizer (RDF) at 100%, 75%, and 50%, each combined with two rounds of foliar sprays using nano urea and nano DAP (first spray and a second spray 15 days later), along with conventional urea and DAP sprays, and a TNAU Pulse Wonder spray. Ten treatments were tested, each replicated three times in a randomized block design (RBD). Physiological (chlorophyll content), biochemical (soluble proteins, nitrate reductase activity), and microbiological (nodule number, microbial population) parameters were recorded at critical growth stages. The combination of 100% RDF with two nano DAP sprays resulted in significantly higher total chlorophyll concentration (increases of 21.4%, 10.7%), soluble protein content (increases of 30.5%, 15.7%), and nitrate reductase activity (increases of 30.1%, 14.7%), with values at par with 75% RDF + nano DAP foliar sprays twice, as well as 100% RDF + TNAU Pulse Wonder in comparison to 100% RDF with conventional DAP sprays, respectively observed after 1st spray. Notably, the 50% RDF + nano DAP significantly increased nodule number and microbial population at critical stages. Overall, the data demonstrated that 75% RDF + foliar spray of nano DAP (twice) has improved physiological and biochemical changes in green gram plants, indicating a potential saving of phosphorus fertilizers by up to 25%. Physiological responses were more pronounced with nano DAP than conventional DAP, likely due to its rapid absorption, quick assimilation and improved use efficiency.