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

Abstract

Fertiliser 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, NH 3-N and N 2 ON 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, NH 3-N emissions were significantly reduced under the IU treatment, by 48-65%. No significant differences in cumulative N 2 O 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.

An evaluation of four years of nitrous oxide fluxes after application of ammonium nitrate and urea fertilisers measured using the eddy covariance method

“…Field site and management Measurements were made at the permanent Easter Bush field site in the Easter Bush Estate (Midlothian, UK, 55°51'57.4"N 3°12'29.3"W) (Cowan et al, 2016;Jones et al 2017Jones et al ) during 2012Jones et al , then in 2016Jones et al , 2017Jones et al and 2018. The site consisted of a small enclosed area in which a permanently stationed, temperature controlled cabin with access to mains power was located directly between two similarly managed grazed grasslands (North and South fields, each approximately 5.4 ha, Figure 1).…”

Application of Bayesian statistics to estimate nitrous oxide emission factors of three nitrogen fertilisers on UK grasslands

“…The EB field had historically been used to graze sheep (0.7 LSU ha −1 ) The UJ field had predominantly been used for silage harvest with occasional grazing during winter. The HF and NW sites were managed similarly, predominantly used for silage harvest with occasional grazing during winter months (Carswell et al, 2018).…”

“…Gas samples were stored in pre-evacuated 20 ml glass vial, which were flushed with 50 ml of air from the syringe using a double needle. Samples were analysed for N 2 O concentration using a Perkin Elmer 580 Gas Chromatograph (linked to a TurboMatrix 110 Headspace Autosampler) (Carswell et al, 2018). At the HF and NW sites manual static chamber measurements were carried out following fertilisation at three times weekly for weeks one and two, twice weekly for weeks three and four, and once weekly thereafter.…”

“…Microbial inhibitors and compounds which block enzymes of microbially mediated pathways are also in development (Sanz-Cobena et al, 2016; Ni et al, 2014; Singh et al, 2013; Rose et al, 2017; Ruser and Schulz, 2015). Although there are many positive studies, which promote the pollution-reducing capabilities of these inhibitors, especially the reduction of NH 3 losses, some questions remain over the overall effectiveness of the inhibitors, which face claims that reduction of NH 3 losses may increase N 2 O emissions (Lam et al, 2016; Carswell et al, 2018).…”

Plant-Dependent Soil Bacterial Responses Following Amendment With a Multispecies Microbial Biostimulant Compared to Rock Mineral and Chemical Fertilizers

“…In grassland systems where the aim is to promote plant biomass, application of fertilizers is the most common and important management practice ( Ikoyi et al, 2018 ; Carswell et al, 2019 ). However, the use of biostimulants to compliment fertilizers is gaining interest ( Caradonia et al, 2019 ).…”