Assessing the benefits and wider costs of different N fertilisers for grassland agriculture

Alison Carswell,Rory Shaw,John Hunt,Antonio Rafael Sánchez-Rodríguez,Karen Saunders,Joseph Cotton,Paul W Hill,Dave R Chadwick,Davey L Jones,Tom H Misselbrook

doi:10.1080/03650340.2018.1519251

Alison Carswell, Rory Shaw + Show 8 more

Open Access

https://doi.org/10.1080/03650340.2018.1519251

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Abstract

ABSTRACTFertiliser nitrogen (N) is essential for maintaining agronomic outputs for our growing population. However, the societal, economic and environmental impacts of excess reactive N from fertiliser is rarely assessed. Here the agronomic, economic and environmental efficacy of three N-fertiliser sources, ammonium-nitrate (AN), urea (U), and inhibited-urea (IU; with NPBT) were evaluated at two grassland sites. Dry matter yield and herbage quality were measured at each silage-cut. Additionally, NH3-N and N2O-N losses were measured and used to calculate the effective N source cost and externality costs, which account for associated environmental and societal impacts. We found no effect of different N sources on yield or herbage quality. However, NH3-N emissions were significantly reduced under the IU treatment, by 48–65%. No significant differences in cumulative N2O emissions were observed. Incorporating externality costs increased fertiliser prices by 1.23–2.36, 6.51–16.4, and 3.17–4.17 times the original cost, for AN, U and IU, respectively, transforming U from the cheapest, to the most expensive of the N sources examined. However, with no apparent yield differences between N-fertiliser sources there is no economic incentive for the land-manager to use the more environmentally and socially acceptable option, unless externality costs are incorporated into fertiliser prices at the point of sale.

Highlights

Nitrogen (N) fertilisers are essential for feeding and maintaining our rapidly growing global population
We examined the performance of AN, U and inhibited urea (IU) (NBPT as the urease inhibitor; Agrotain®; from Koch Agronomic Service), along with a control (C; without N addition) at two intensive grassland sites, both managed as three-cut silage systems
There was a significant interaction between fertiliser treatment and harvest, which can be attributed to the performance of C (Figure 1)

Summary

Introduction

Nitrogen (N) fertilisers are essential for feeding and maintaining our rapidly growing global population. Through the production and use of synthesised N fertiliser, the global N cycle has become massively disrupted (Rockström et al 2009). The production of N fertiliser reached 104–113 M tonnes N year−1 (years 2010 – 2014; FAO 2016). Nitrogen fertilisers are reactive and, where they are not efficiently used by the target crop, can quickly be transported out of the agricultural system. A recent estimate of full chain N use efficiency (NUE) across 24 EU countries, where NUE was calculated based on N input as fertiliser and N outputs in the final foodstuff, was just over 30% (Erisman et al 2015)

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