Influence of urea fertiliser formulation, urease inhibitor and season on ammonia loss from ryegrass

Abstract

This paper reports the results of experiments to determine whether ammonia (NH 3) loss can be reduced and nitrogen (N) use efficiency improved by using two relatively new commercial urea formulations rather than granular urea and urea ammonium nitrate. Four nitrogen treatments were applied at a rate of 40 kg N ha-1 : granular urea, "Green Urea 14™" [containing 45.8% nitrogen (N) as urea and "Agrotain®" (N-(n-butyl) thiophosphoric triamide) @ 5 L t-1 of urea as a urease inhibitor], "Nhance", a fine particle spray [containing 46% N as urea, "Agrotain" @ 1 L t-1 of urea and gibberellic acid (applied at a rate of 10 g ha-1)] and urea ammonium nitrate in solution (UAN) surface applied. Ammonia loss was determined in autumn and spring using a micrometeorological method. In autumn, use of the Green Urea and Nhance reduced NH 3 loss from the 30% of applied N lost from the granular urea to 9% and 23% respectively. Loss from all treatments in spring was very small (less than 2% of applied N), because 4 mm of rain fell within 24 hours of application onto an already wet site. The use of the Nhance and Green Urea instead of granular urea did not result in increased agronomic efficiency or recovery efficiency of the applied N, and this is most likely due to the presence of sufficient available N from both fertiliser application and the soil. A 15 N study recovered 72.8% of the applied N in the plants and soil, and showed that 30% of the total N taken up by the plant was derived from the fertiliser, and 70% from the soil.

Influence of enhanced efficiency fertilisation techniques on nitrous oxide emissions and productivity response from urea in a temperate Australian ryegrass pasture

“…The agronomic efficiency (kg pasture increase per kg N applied) and apparent recovery of N (net kg N taken up per kg N applied) were significantly (P < 0.05) greater in spring (September to October) and December than in autumn and winter, reflecting the seasonal pattern of pasture production for the region as reported by Suter et al (2013) (Table 2). The lowest response to N occurred in July (average 7.7 AE 0.3 kg DM per kg of N for fertiliser treatments) where pasture was cut at 42 DAF (Table 2) due to low mineral N available for pasture growth (Fig.…”

“…Details of the site characteristics are described in Suter et al (2013). Briefly, the Chromosol soil (Isbell 1996) has a topsoil (0-10 cm) with a silty loam texture (22% clay, 38% silt, 40% sand, from 0-25 cm depth), a pH CaCl 2 of 4.6, 0.2% total N, 2.7% total C, a bulk density of 1.23 g cm -3 , and a cation exchange capacity (CEC) of 4.98 cmol (+) kg soil À1 .…”

“…This results from decreased NH 3 loss, leading to greater N remaining in the soil. A concurrent study of NH 3 loss at the site found that using NBTPT decreased N loss as NH 3 in autumn to 3.7 kg N from 12 kg N with urea (Suter et al 2013). However, in July and September 2010 the higher rainfall and soil moisture (Figs 1 and 2) would lower the potential for NH 3 loss from urea so no additional N would be 'saved' in the urease inhibitor treatment, indicating no benefit from using the urease inhibitor at this time.…”

“…The greatest impact of elevated emissions from the urease inhibitor occurred after the 16 July 2010 application. This was unexpected because in July NH 3 loss was assumed to be low, based on winter climatic conditions, and in September the measured NH 3 loss was low (Suter et al (2013). So, the applied N remaining in the soil for the U and GU treatments should have been similar, but for GU the urea 23 December C 58 ± 9a 667 ± 42a 545 ± 40a 419 ± 15a U 116 ± 22b 1079 ± 149a 859 ± 150a 661 ± 146a DMPP 97 ± 9ab 764 ± 55a 575 ± 58a 431 ± 63a GU 115 ± 6b 1711 ± 265b 1480 ± 250b 1228 ± 230b FPA 94 ± 15ab NA NA NA would have been released more slowly making the substrate for nitrification and N 2 O production available for longer compared with urea.…”

“…A review of the literature shows that across a range of crops and pastures, use of a urease inhibitor led to a 20% to 88% decrease in NH 3 volatilisation compared with urea (Watson et al 1990;Rawluk et al 2001;Turner et al 2010;Suter et al 2013). Due to the impacts on NH 3 volatilisation, it is expected that N 2 O emissions may increase relative to urea because of greater N in the system, but some studies have reported decreases in N 2 O with the urease inhibitor (Zaman et al 2009;Singh et al 2013;Ding et al 2014).…”