Particle Size Impacts Of Subsurface-Banded Urea On Nitrogen Transformation In The Laboratory

Replacing commercial urea granules (0.01-0.02 g) with urea pellets (1.5 g) could improve crop yield and reduce nitrogen (N) losses into the environment. Since urea particle size affects N transformations and, subsequently, N-loss pathways, laboratory studies were conducted to study the effects of subsurface-banded urea. particle size or specific surface area (SSA) effects on dissolution; mechanism of dissolved urea movement, and N mineralization (urea hydrolysis and nitrification). To simulate subsurface banding, urea treatments were applied in a plane beneath the soil to Ross loam soil at volumetric soil moisture content (0,) of 31.4% (34 chars) in all studies. At 50% dissolution, granules dissolved eight times faster than 1.5-g pellets. Molecular diffusion was likely the predominant mechanism of dissolved urea movement in both pellets and granules. Urea hydrolysis was significantly lower by 3.1% in 1.5-g pellets than in granules after 7 d. At 35 d, nitrification rate of the applied-N was 11% (significantly) lower in 1.5-g pellets than granules. Compared with granules, pellets dissolved slower and inhibited both urease and nitrifier activity to a greater extent; however, nitrification inhibition was likely the predominant mechanism that reduced nitrate availability for both uptake and loss. Hence, when granules and 1.5-g pellets are both subsurface-banded in the soil, slower nitrification in pellets could reduce the potential for N losses. However, greater benefits in terms of increased crop yield and N uptake and, potentially, reduced N losses are likely when surface-broadcast urea granules are replaced with subsurface-applied urea pellets.