Statistical analysis of nitrous oxide emission factors from pastoral agriculture field trials conducted in New Zealand

Abstract

Between 11 May 2000 and 31 January 2013, 185 field trials were conducted across New Zealand to measure the direct nitrous oxide (N2O) emission factors (EF) from nitrogen (N) sources applied to pastoral soils. The log(EF) data were analysed statistically using a restricted maximum likelihood (REML) method. To estimate mean EF values for each N source, best linear unbiased predictors (BLUPs) were calculated. For lowland soils, mean EFs for dairy cattle urine and dung, sheep urine and dung and urea fertiliser were 1.16 ± 0.19% and 0.23 ± 0.05%, 0.55 ± 0.19% and 0.08 ± 0.02% and 0.48 ± 0.13%, respectively, each significantly different from one another (p < 0.05), except for sheep urine and urea fertiliser. For soils in terrain with slopes >12°, mean EFs were significantly lower. Thus, urine and dung EFs should be disaggregated for sheep and cattle as well as accounting for terrain.

Nitrous oxide emission factors for urine and dung from sheep fed either fresh forage rape (Brassica napus L.) or fresh perennial ryegrass (Lolium perenne L.)

“…However, a number of previous studies have suggested that the majority of emissions occur during the first 3 or 6 months after application of animal urine or dung, respectively (e.g. Kelliher et al, 2013;Luo et al, 2013;van der Weerden et al, 2013).…”

“…This was probably owing to the differences in CP levels in the two different diets (Table 1). Kelliher et al (2013) found that there was a direct relationship between the concentration of N in livestock feed and the proportion of N excreted as urine.…”

“…However, a number of previous studies have suggested that the majority of emissions occur during the first 3 or 6 months after application of animal urine or dung, respectively (e.g. Kelliher et al, 2013;Luo et al, 2013;van der Weerden et al, 2013).Gas samples were analysed using a gas chromatograph equipped with a 63 Ni-electron capture detector. Hourly N 2 O fluxes were calculated for each chamber from the increase in headspace N 2 O concentration over the sampling time (associated measurements showed that this occurred at a linear rate).…”

“…This was probably owing to the differences in CP levels in the two different diets (Table 1). Kelliher et al (2013) found that there was a direct relationship between the concentration of N in livestock feed and the proportion of N excreted as urine.The forage rape contained more readily fermentable and less structural carbohydrates than ryegrass (Table 1). Thus, animals on the forage rape diet would be expected to retain a greater proportion of their ingested N than on a ryegrass…”

Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

“…Superimposed on this variation are the further impacts associated with soil type such as differences in physical characteristics, such as texture and bulk density (which impact WFPS), chemical characteristics such as soil C, N and pH, and biological properties such as the proportion of fungi and bacteria (van der Weerden et al, 2012, Kelliher et al, 2014.…”