Effect of enhanced efficiency fertilisers on nitrous oxide emissions in a sub-tropical cereal cropping system

Abstract

Abstract.To meet the global food demand in the coming decades, crop yields per unit area must increase. This can only be achieved by a further intensification of existing cropping systems and will require even higher inputs of N fertilisers, which may result in increased losses of nitrous oxide (N 2 O) from cropped soils. Enhanced efficiency fertilisers (EEFs) have been promoted as a potential strategy to mitigate N 2 O emissions and improve nitrogen use efficiency (NUE) in cereal cropping systems. However, only limited data are currently available on the use of different EEF products in sub-tropical cereal systems. A field experiment was conducted to investigate the effect of three different EEFs on N 2 O emissions, NUE and yield in a sub-tropical summer cereal cropping system in Australia. Over an entire year soil N 2 O fluxes were monitored continuously (3 h sampling frequency) with a fully-automated measuring system. The experimental site was fertilised with different nitrogen (N) fertilisers applied at 170 kg N ha -1 , namely conventional urea (Urea), urea with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), polymer-coated urea (PCU), and urea with the nitrification inhibitor nitrapyrin (Nitrapyrin). Nitrous oxide emissions were highly episodic and mainly controlled by heavy rainfall events within two months of planting and fertiliser N application. Annual N 2 O emissions in the four treatments amounted to 2.31, 0.40, 0.69 and 1.58 kg N 2 O-N ha -1 year -1 for Urea, DMPP, PCU and Nitrapyrin treatments, respectively, while unfertilised plots produced an average of 0.16 kg N 2 O-N ha -1 year -1 . Two of the tested products (DMPP and PCU) were found to be highly effective, decreasing annual N 2 O losses by 83% and 70%, respectively, but did not affect yield or NUE. This study shows that EEFs have a high potential to decrease N 2 O emissions from sub-tropical cereal cropping systems. More research is needed to assess if the increased costs of EEFs can be compensated by lower fertiliser application rates and/or yield increases.

Comparison of grain yields and N2O emissions on Oxisol and Vertisol soils in response to fertiliser N applied as urea or urea coated with the nitrification inhibitor 3,4-dimethylpyrazole phosphate

“…Notably, the substantial rainfall events later in the cropping season (178 mm fell from mid-February to mid-April 2014 at the Oxisol site) did not generate high N 2 O emissions, indicating that by then most of the applied N was probably taken up by plants, immobilised by microbes, lost to the environment or deeper in the soil profile. These observations of the majority of N 2 O emissions being recorded within 90 days from fertilisation are in good agreement with the results of other studies on Australian subtropical summer cropping systems on Vertisols and Oxisols (Scheer et al 2013(Scheer et al , 2016bDe Antoni Migliorati et al 2014).…”

“…These were 160 and 120 kg N ha -1 on the Vertisol and Oxisol respectively. These rates were~30% higher than standard farmer practice (~120 and 90 kg N ha -1 respectively), but considered appropriate due to the preceding very wet summer with large denitrification losses Scheer et al 2016b) and the use of winter forage crops to ensure low starting profile N. * Urea (UREA-R): in both soils conventional urea was applied at a reduced rate (80 kg N ha -1 ) that was more comparable to standard farming practice in each region. The N rate was reduced to assess crop response and N 2 O emissions at suboptimal N rates.…”

Greenhouse gas (N2O and CH4) fluxes under nitrogen-fertilised dryland wheat and barley on subtropical Vertosols: risk, rainfall and alternatives

“…Soil sampling conducted 1 month after sowing found less mineral N in the soil than would be expected from the amount added in fertiliser, indicating substantial N loss from the surface soil through denitrification and nitrate leaching. Because the N-fertilised soil did not affect postharvest N 2 O emissions, the critical period for N 2 O loss was the first 2-3 months after application of N fertiliser (Scheer et al 2016). By contrast, the N fertiliser applied at the 2011 sowing remained largely intact as soil mineral N for the next 2 months due to below-average moisture conditions (Fig.…”

Agronomic responses of grain sorghum to DMPP-treated urea on contrasting soil types in north-eastern Australia

“…A contradiction therefore exists between how DMPP can decrease N 2 O emission by over 60% De Antoni Migliorati et al 2015;Scheer et al 2016), but only nominally increases grain yield. The explanation may partly lie in the higher N application rates.…”

“…The effectiveness of nitrification inhibitors (and other EEFs) have been demonstrated to be strongly dependent on site-specific conditions, soil texture and climate (Irigoyen et al 2003). Reduction in N 2 O emissions over the summer period from the use of DMPP-treated urea has been substantial De Antoni Migliorati et al 2015;Scheer et al 2016); however, there are no published studies evaluating the agronomic impacts of DMPP-treated urea on grain sorghum production in subtropical environments. Our study found that DMPP had a nominal grain yield advantage when considered over all the research sites in this study and this was only apparent at the higher fertiliser N application rates (Fig.…”