Vegetable Plant Canopy Inhibits Soil Urease Activity and Reduces NH₃ Losses Under p-Phenylenediamine (PPD)-Coated Urea Application

Nitrogen ( N) losses from agricultural soils deteriorate environment, through NH3 depositions, and limit the agricultural productivity. Urea-N loss is considered to be minimized through urea hydrolysis inhibition by using various synthetic and natural soil urease inhibitors. However, the contribution of vegetable plant canopy towards soil urease inhibition is not well documented. In this study, eight vegetable species, viz., Capsicum annum, Capsicum frutescens, Solanum lycopersicum, Cucumis sativus, Allium cepa, Brassica oleracea, Cucurbita pepo, and Solanum melongena, were investigated for soil urease activity (SUA) at three transplanting intervals (15, 30, and 45 days after transplantation (DAT)) and two sampling depths (0-4.5 cm and 4.5-9.0 cm) under PPD (p-phenylenediamine) 1.0%-coated, HQ (hydroquinone) 2.0%-coated, and/or uncoated urea (pure urea) applications during February-May, 2021. The SUA was found to be reduced by 19%, 21%, 18%, 15%, and 30% in soils cultivated with C. annum, C. frutescens, C. sativus, C. pepo, and S. melongena, respectively, at 15 DAT with respect to 30 DAT. Similarly, except C. pepo, all the vegetable canopies significantly reduced SUA at 4.5- 9.0 cm in comparison to 0- 4.5 cm soil depth. The reduction of SUA, subsequently, reduced NH3 loss by similar to 50%, on an average, under PPD 1.0%-coated urea in comparison to uncoated urea application with fruit yield enhancements in C. annum (238.3 g plant(-1)) and C. frutescens (45.9 g plant(-1)). Altogether, the impact of vegetable plant canopies was found significant in reducing SUA at 15 DAT and 4.5-9.0 cm of sampling depth under PPD 1.0%-coated urea application.