The relationship between N2O, NO, and N2 fluxes from fertilized and irrigated dryland soils of the Aral Sea Basin, Uzbekistan

Abstract

Microbial respiratory reduction of nitrous oxide (N 2 O) to dinitrogen (N 2 ) via denitrification plays a key role within the global N-cycle since it is the most important process for converting reactive nitrogen back into inert molecular N 2 . However, due to methodological constraints, we still lack a comprehensive, quantitative understanding of denitrification rates and controlling factors across various ecosystems. We investigated N 2 , N 2 O and NO emissions from irrigated cotton fields within the Aral Sera Basin using the He/O 2 atmosphere gas flow soil core technique and an incubation assay. NH 4 NO 3 fertilizer, equivalent to 75 kg ha −1 and irrigation water, adjusting the water holding capacity to 70, 100 and 130% were applied to the incubation vessels to assess its influence on gaseous N emissions. Under soil conditions as they are naturally found after concomitant irrigation and fertilization, denitrification was the dominant process and N 2 the main end product of denitrification. The mean ratios of N 2 /N 2 O emissions increased with increasing soil moisture content. N 2 emissions exceeded N 2 O emissions by a factor of 5±2 at 70% soil water holding capacity (WHC) and a factor of 55±27 at 130% WHC. The mean ratios of N 2 O/NO emissions varied between 1.5±0.4 (70% WHC) and 644±108 (130% WHC). The magnitude of N 2 emissions for irrigated cotton was estimated to be in the range of 24±9 to 175±65 kg-N ha −1 season −1 , while emissions of NO were only of minor importance (between 0.1 to 0.7 kg-N ha −1 season −1 ). The findings demonstrate that for irrigated dryland soils in the Aral Sera Basin, denitrification is a major pathway of N-loss and that substantial amounts of Nfertilizer are lost as N 2 to the atmosphere for irrigated dryland soils.

Emission factors for estimating fertiliser-induced nitrous oxide emissions from clay soils in Australia’s irrigated cotton industry

“…The latter value is at the upper level of N 2 O emissions from the limited amount of data available for irrigated cotton reported from other countries (Mahmood et al 2008;Scheer et al 2008;Liu et al 2010;Watts et al 2015) and of a similar magnitude to that reported by Grace et al (2004) at the same site. Scheer et al (2008) reported a comparable response to N in irrigated cotton in Uzbekistan (6.5 kg N 2 O-N ha -1 ) after application of 250 kg N ha -1 . The Australian cotton studies were all undertaken on alkaline heavy black clays that rapidly become anaerobic, producing ideal conditions for prolonged periods of denitrification (Rochester 2003) compared with the relatively free-draining sandy loams and loams studied in other countries.…”

NOX fluxes from several typical agricultural fields during summer-autumn in the Yangtze Delta, China

“…Accordingly, the reported fertilizer-induced NO emission ratios varied from 0.003% to 11% (Yan et al, 2003). Although many studies have investigated the exchange of NO X between various agricultural fields and the atmosphere Stohl et al, 1996;Veldkamp and Keller, 1997;Zheng et al, 2003a,b;Mu, 2006, 2007;Scheer et al, 2009;Yu et al, 2008), the available data are still limited to accurately estimate NO emissions from agricultural fields. In the empirical model of Yienger and Levy (1995), 2.5% of the fertilizer N applied to soil was assumed to be emitted as NO (based on the arithmetic mean of eight reports).…”

Effect of soil saturation on denitrification in a grassland soil

“…Davidson et al (1991) provided a WFPS threshold for determination of source process, with a value of 60 % WFPS as the borderline between nitrification and denitrification as source processes for N 2 O production. The WFPS in all treatments in our study was larger than 70 %, above this 60 % threshold, and referred to as the "optimum water content" for N 2 O by Scheer et al (2009), so we can be confident that denitrification was likely to have been the main Table 7 source process in our experiment. In addition, Bateman et al (2004) observed the largest N 2 O fluxes at 70 % WFPS on a silty loam soil, lower than the 80 % value for the largest fluxes from the clay soil in our study (Fig.…”