Ammonia emissions from urea, stabilized urea and calcium ammonium nitrate: insights into loss abatement in temperate grassland

Abstract

Fertiliser nitrogen (N) contributes to ammonia (NH 3 ) emissions, which European Union member states have committed to reduce. This study evaluated NH 3 -N loss from a suite of N fertilisers over multiple applications, and on gaining insights into the temporal and seasonal patterns of NH 3 -N loss from urea in Irish temperate grassland using wind tunnels. The fertilisers evaluated were: calcium ammonium nitrate (CAN), urea, and urea with the N stabilisers N-(n-butyl) thiophosphoric triamide (NBPT), dicyandiamide (DCD), DCD+NBPT, and a maleic and itaconic acid polymer (MIP). 200 (and 400 for urea only) kg N/ha/yr was applied in five equal applications over the growing season at two grassland sites (one for MIP). Mean NH 3 -N losses from CAN were 85% lower than urea which had highly variable loss (range 45% points). The effect of DCD on NH 3 emissions was variable. MIP did not decrease loss but NBPT caused a 78.5% reduction, and when combined with DCD, a 74% reduction compared with urea alone. Mean spring and summer losses from urea were similar, although spring losses were more variable with both the lowest and highest loss levels.Maximum NH 3 -N loss usually occurred on the second day after application. These data highlight the potential of stabilised urea to alter urea NH 3 -N loss outcomes in temperate grassland, the need for caution when using season as a loss risk guide and that urea hydrolysis and NH 3 -N loss in temperate grassland is rapid. Micrometeorological measurements focused specifically on urea are needed to determine absolute NH 3 -N loss levels in Irish temperate grassland.

Can the agronomic performance of urea equal calcium ammonium nitrate across nitrogen rates in temperate grassland?

“…() detected an N offtake advantage for AN over urea. The use of NBPT has been shown to reduce ammonia losses from urea in temperate grassland (Watson et al ., , ; Forrestal et al ., ). Treatment of urea with NBPT resulted in N offtake and AFNR which consistently equalled CAN across N rates (Figure b,c), indicating that urea can give a consistent agronomic performance at least equal to CAN when it is treated with NBPT.…”

“…Wind tunnel experiments to measure ammonia loss from urea in UK grasslands have reported mean emissions of 30% for urea (Chambers & Dampney, ). Similar mean annual values of 25.1 and 30.6% were reported for JC14 and HB14, respectively, in wind tunnel experiments (Forrestal et al ., ) run in parallel to the current study to test the comparative ammonia loss performance of several fertilizer N types. Nitrogen offtake data from the current study can be used to provide a coarse comparison with the losses measured by the wind tunnels and of ammonia loss in temperate maritime grassland.…”

“…The dominant grass species in the sward at each location was perennial ryegrass ( Lolium perenne L.). Parallel studies also measured nitrous oxide emissions at all site‐years (Harty et al ., ) and ammonia emissions at two site‐years (HB14 and JC14) (Forrestal et al ., ).…”

“…Urease inhibitors such as N‐(n ‐ butyl) thiophosphoric triamide (NBPT) present an opportunity to overcome the uncertainty associated with ammonia losses from urea. Treatment with NBPT effectively reduces ammonia loss from urea applied to grassland soils (Watson et al ., ; Chambers & Dampney, ; Forrestal et al ., ) because, in soil, NBPT rapidly converts to its oxygen analog, NBPTo (Engel et al ., ) which inhibits the urease enzyme.…”

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

“…This study was carried out in a glass-house setup with soil samples representative of New Zealand pastures. Urea fertilizer with Agrotain has also been found to reduce the loss of ammonia by 24-70% compared to unaltered urea fertilizer when applied to ryegrass (Suter et al 2013), and a 78% reduction in ammonia emissions was observed when urea was applied with NBPT to the grassland (Forrestal et al 2016).…”