Ammonia volatilization following surface application of urea to tilled and no-till soils: A laboratory comparison

Abstract

Broadcasting of urea to agricultural soils can result in considerable losses by NH 3 volatilization. However, it is unclear if the impact of this practice on NH 3 emissions is further enhanced when performed on no-till (NT) soils. The objective of this study was to compare NH 3 volatilization following broadcasting of urea to NT and moldboard plowed (MP) soils. Intact soil cores were taken shortly after harvest from NT and MP plots of three long-term tillage experiments in Québec (Canada) and stored for 4.5 months prior to incubation. Urea (14 g N m −2) was applied at the soil surface and NH 3 volatilization was measured for 30 d using an open incubation system. Mean cumulative NH 3 losses were greater ( P < 0.001) in NT (3.00 g N m −2) than in MP (0.52 g N m −2). Several factors may have contributed to the higher emissions from the NT soils. Urease activity in the top 1 cm of soils was on average 4.2 times higher in NT than in MP soils. As a result, hydrolysis of urea occurred very rapidly in NT soils as indicated by enhanced NH 3 emissions 4 h after application of urea. The presence of crop residues at the surface of NT soils also decreased contact of the urea granules with the soil, possibly reducing adsorption of NH 4 + on soil particles. Lower volatilization on the MP soils may also have partly resulted from a fraction of urea granules falling into shallow cracks. Field trials are needed to confirm our finding that NT soils bear greater potential for NH 3 volatilization following surface application of urea than MP soils.