Ammonium-Based Compound Fertilisers Mitigate Nitrous Oxide Emissions in Temperate Grassland

Abstract

Nitrogen fertiliser application represents the largest anthropogenic source of nitrous oxide (N2O) emissions, and the magnitude of these emissions is dependent on the type of fertilisers applied in the agroecosystems. Despite N-P-K compound fertilisers being commonly used in agricultural soils, a lack of information exists regarding their effects on N2O emissions. This study aims at examining the effects of different commonly used N-P-K compound fertiliser formulations with contrasting nitrate to ammonium ratios (0.05 to 0.88) on N2O emissions, yield, and nitrogen use efficiency (NUE) in temperate grassland and to compare these variables with common straight N fertilisers. Compound fertilisers with varying NPK inclusion rates (18-6-12, 10-10-20, 24-2.2-4.5, and 27-2.5-5), and calcium ammonium nitrate (CAN) and urea + N-(n-butyl) thiophosphoric triamide (NBPT) were applied at 80 kg N ha−1 to experimental plots in managed grassland on two occasions in a growing season. Fluxes of N2O during the experiment period, yield and NUE following two harvests were measured. The cumulative N2O emission from urea + NBPT, 18-6-12, 10-10-20, and 24-2.2-4.5 treatments were significantly reduced by 44%, 43%, 37%, and 31% compared with CAN treatment under conducive soil moisture condition. Under the same soil condition, 18-6-12 and 10-10-20 treatments showed higher yield, N uptake, and NUE although did not significantly differ from the other fertiliser treatments. Our results suggest that ammonium-based compound fertilisers have a potential to reduce N2O emissions while maintaining yields. Further long-term study is needed to capture the full magnitude of variations in N2O emissions, including ammonia (NH3) volatilization from nitrate and ammonium-based compound fertiliser applications from multiple soil types and under different climatic conditions.

Optimising soil P levels reduces N2O emissions in grazing systems under different N fertilisation

“…Cumulative N 2 O was significantly greater in P0 soils receiving KNO 3 and (NH 4 ) 2 SO 4 treatments than in P30 soils. N 2 O emissions have frequently been reported to be higher from nitrate‐containing fertilisers compared to urea or ammonium fertilisers due to the immediate availability of the nitrate substrate for denitrification in wet temperate grassland soils (Cowan et al, 2020; Gebremichael et al, 2021; Harty et al, 2016; Krol et al, 2020; Rahman et al, 2021). Interestingly, although the current study was carried out under comparable conditions, our results contrasted with these studies, with the ammonium treatment ((NH 4 ) 2 SO 4 ) yielding numerically (although not statistically significant) greater levels of N 2 O than the KNO 3 treatment (Figure 3).…”

“…The fresh grass cut from each plot was weighed and oven dried at 70°C for dry matter determination (by dividing dry weight by the fresh weight). Grass dry matter yield (DMY) was expressed as g ha −1 and was computed using fresh weight from the collar area and the dry matter content (Gebremichael et al, 2021). N‐uptake was calculated by multiplying the dry matter yield by the N content of the dry matter sample: Nitrogen use efficiency (NUE %) was calculated by dividing the difference between N‐uptake of treatment and control by the applied rate of N and expressing as a percentage: …”

Ammonium Fertilizer Reduces Nitrous Oxide Emission Compared to Nitrate Fertilizer While Yielding Equally in a Temperate Grassland

“…The EFs generated in previous work for urea and CAN do not best represent these compound fertilizers with differing nitrate to ammonium ratios. A recently published short-term study by Gebremichael et al [17] with artificial watering to promote emissions showed nitrate to ammonium ratios (NO 3 − :NH 4 + = 0.05, 0.53, 0.80, 0.88) for the commonly used compound fertilizers (10-10-20, 18-06-12, 27-2.5-5 and 24-2.2-4.5). Emission measurements conducted in July and August 2021 showed an average N 2 O loss of 1.8% from ammonium-based (NO 3 − :NH 4 + = 0.05 and 0.53) and 2.37% from nitrate-based (NO 3 − :NH4 + = 0.80 and 0.88) compound fertilizers.…”

“…This is a significant knowledge gap for the development of abatement strategies, for our understanding of the relative weighting of the NO 3 − -N and the NH 4 + -N portions in driving N 2 O losses from ammonium nitrate or compound fertilizers. For emission inventory calculations it is clear that N 2 O losses from several blended/compound products are not best characterized by either CAN/AN or urea emission factors which are abundant [17]. The direct comparison of fully ammonium with fully nitrate fertilizers is very scarce.…”

“…The direct comparison of fully ammonium with fully nitrate fertilizers is very scarce. In a recent work, Gebremichael et al [17] performed a shortterm experiment of three months, and the authors make the case that ammonium-based compound fertilizers have the potential to reduce N 2 O emissions compare to nitrate-based fertilizers and suggested a long-term study to capture the yearly N 2 O-EF. In the present study, an ammonium and a nitrate N 2 O-EF is measured which can be used to provide new information to characterize differences in N 2 O emissions between NO 3 − -N and NH 4 + -N in temperate grassland.…”