Search

Agricultural land occupies nearly half of the earth's surface, and farming activities account for nearly 60% of total anthropogenic N2O emissions. The manufactured nitrogen (N) fertilizers applied to soils are major sources of N2O emissions from agricultural systems. Among the synthetic N fertilizers, urea has the highest nitrogen content of all solid nitrogenous fertilizers and accounts for 66% of global synthetic N fertilizer use. Hence, efficient urea-N management is imperative for global N2O abatement. This review provides an update on advances in N2O-generating pathways, microbial mechanisms, abiotic and biotic regulating factors, and mitigation strategies. Nitrification inhibitors have been extensively studied as strategies to mitigate soil N2O emissions by decreasing nitrification and denitrification processes. Controlled/slow-release fertilizer formulations have been used widely to enhance fertilizer N use efficiency by regulating the release rates of N from fertilizer. Additionally, biochar, microbial inoculation with arbuscular mycorrhizal fungi (AMF), biological nitrification inhibitors (BNIs) and biological denitrification inhibitors (BDIs) may enable the development of novel and environment‐friendly strategies for practicable N2O mitigation in future. [ABSTRACT FROM AUTHOR]

Nitrous oxide ([N.sub.2]O) emissions from sugarcane cropped soils are usually high compared with those from other arable lands. Nitrogen-efficient management strategies are needed to mitigate [N.sub.2]O emissions from sugarcane farming whilst maintaining productivity and profitability. A year-long field experiment was conducted in wet tropical Australia to assess the efficacy of polymer-coated urea (PCU) and nitrification inhibitor (3,4-dimethylpyrazole phosphate)-coated urea (NICU). Emissions of [N.sub.2]O were measured using manual and automatic gas sampling chambers in combination. The nitrogen (N) release from PCU continued for >5-6 months, and lower soil N[O.sub.3.sup.-] contents were recorded for ≥ 3 months in the NICU treatments compared with the conventional urea treatments. The annual cumulative [N.sub.2]O emissions were high, amounting to 11.4-18.2 kg [N.sub.2]O-N [ha.sup.-1]. In contrast to findings in most other cropping systems, there were no significant differences in annual [N.sub.2]O emissions between treatments with different urea formulations and application rates (0, 100 and 140 kg N [ha.sup.-1]). Daily variation in [N.sub.2]O emissions at this site was driven predominantly by rainfall. Urea formulations did not significantly affect sugarcane or sugar yield at the same N application rate. Decreasing fertiliser application rate from the recommended 140 kg N [ha.sup.-1] to 100 kg N [ha.sup.-1] led to a decrease in sugar yield by 1.3t [ha.sup.-1] and 2.21 [ha.sup.-1] for the conventional urea and PCU treatments, respectively, but no yield loss occurred for the NICU treatment. Crop N uptake also declined at the reduced N application rate with conventional urea, but not with the PCU and NICU. These results demonstrated that substituting NICU for conventional urea may substantially decrease fertiliser N application from the normal recommended rates whilst causing no yield loss or N deficiency to the crop. Further studies are required to investigate the optimal integrated fertiliser management strategies for sugarcane production, particularly choice of products and application time and rates, in relation to site and seasonal conditions. Additional keywords: controlled-release fertiliser, DMPP, greenhouse gas, [N.sub.2]O, nitrification inhibitor, urea., Introduction The efficiency of fertiliser nitrogen (N) use by sugarcane (Saccharum officinarum L.) crops is generally low, with ~40-60% of the applied N lost from the plant-soil system (Vallis el [...]

In sugarcane cropping systems, high rates of N fertiliser are typically applied as sub-surface bands creating localised zones of high mineral N concentrations. This in combination with high levels of crop residue (trash) retention and a warm and humid climate creates conditions that are known to promote soil denitrification, resulting in high emissions of the potent greenhouse gas N2O. These losses illustrate inefficient use of N fertilisers but total denitrification losses in the form of N2 and N2O remain largely unknown. We used the 15N gas flux method to investigate the effect of cane trash removal and the use of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N2 and N2O emissions on a commercial sugarcane farm at Bundaberg, Australia. High gaseous N losses were observed under the standard grower practice where cane trash retention and N fertiliser application (145 kg N ha−1 as urea) resulted in N2 and N2O emissions (36.1 kg N ha−1) from the subsurface N fertiliser band, with more than 50% of these losses emitted as N2O. Cane trash removal reduced N2 emission by 34% and N2O emission by 51%, but had no effect on the N2O/(N2 + N2O) ratio. The use of DMPP lowered N2 and N2O emission by 35% and 98%, respectively, reducing the percentage of these losses (N2 + N2O) emitted as N2O to only 4%. We conclude that the use of DMPP is an effective strategy to reduce N losses, minimise N2O emissions, while keeping the benefits of cane trash retention in sugarcane cropping systems. [ABSTRACT FROM AUTHOR]

The Water and Nitrogen Management Model (WNMM) was applied to simulate nitrous oxide (N20) emissions from a wheat-cropped Vertosol under long-term management of no-till, crop residue retention, and nitrogen (N) fertiliser application in southern Queensland, Australia, from July 2006 to June 2009. For the simulation study, eight treatments of combinations of conventional tillage (CT) or no-till (NT), stubble burning (SB) or stubble retention (SR), and N fertiliser application at nil (ON) or 90 (90N) kg N/ha x year were used. The results indicated that WNMM satisfactorily simulated the soil water content of the topsoil, mineral N content of the entire soil profile (0-1.5 m), and [N.sub.2]O emissions from the soil under the eight treatments, compared with the corresponding field measurements. For simulating daily N20 emissions from soil, WNMM performed best for the treatment CT-SB-90N ([R.sup.2] = 0.48, P Additional keywords: mitigation, N20 emissions, wheat cropping, Vertosol, WNMM simulation., Introduction Nitrous oxide ([N.sub.2]O) is one of the potent greenhouse gases contributing to global warming (IPCC 2006). According to FAO/IFA (2001) and Mosier et al. (1998), ~57% of total global [...]