Exploration of spray-dried micronutrients based nanosuspension concentrate for foliar application to improve banana cropping

Banana Shakti (BS) is a conventional physical mixture of micronutrients containing zinc sulfate, manganese sulfate, ferrous sulfate, copper sulfate, and borax, which has made banana plantations more productive in southern India. The present study used nanotechnology to make BS more soluble and more stable. Initially, the micronutrients were converted into nanoparticles by optimizing the spray-drying process and then formulated into a nanosuspension concentrate, namely ‘Nano Banana Shakti’ (NBS), by stabilizing it with different surfactants at different concentrations (1.5%–3% v/v; NBS1–NBS9). The spray-dried particles were 600 nm on average, with a polydispersity index of 0.54 and a surface charge of 2.78 mV, indicating a moderate size distribution and colloidal stability. The particles were nano-sized, with high surface area, solid-state transition, and elemental identity, and were chemically and thermally stable. Based on initial assessments of their physicochemical properties, NBS2, NBS4, NBS5, and NBS9 were shortlisted and tested at four concentrations (0.25, 0.5, 1, and 2%, w/v) on tissue-cultured banana plants raised in pots. NBS2, containing 3% surfactant-1, showed enhanced dry-matter production (14.5 g/plant, 43.6% greater than that in the control) and higher uptake of macro- and micronutrients at 1% concentration than that recorded either in normal BS at 2% or in the control. The nanosuspension, because it was more soluble and stable and because it led to greater nutrient uptake, proved as effective as the commercial product but at half the dose.