Gaseous emissions and soil fertility of homegardens in the Nuba Mountains, Sudan

Abstract

Intensification of homegardens in the Nuba Mountains may lead to increases in C and nutrient losses from these small-scale land-use systems and potentially threaten their sustainability. This study, therefore, aimed at determining gaseous C and N fluxes from homegarden soils of different soil moisture, temperature, and C and N status. Emissions of CO 2 , NH 3 , and N 2 O from soils of two traditional and two intensified homegardens and an uncultivated control were recorded biweekly during the rainy season in 2010. Flux rates were determined with a portable dynamic closed chamber system consisting of a photo-acoustic multi-gas field monitor connected to a PTFE coated chamber. Topsoil moisture and temperature were recorded simultaneously to the gas measurements. Across all homegardens emissions averaged 4,527 kg CO 2 -C ha -1 , 22 kg NH 3 -N ha -1 , and 11 kg N 2 O-N ha -1 for the observation period from June to December. Flux rates were largely positively correlated with soil moisture and predominantly negatively with soil temperature. Significant positive, but weak (r s < 0.34) correlations between increasing management intensity and emissions were noted for CO 2 -C. Similarly, morning emissions of NH 3 and increasing management intensity were weakly correlated (r s = 0.17). The relatively high gaseous C and N losses in the studied homegardens call for effective management practices to secure the soil organic C status of these traditional land-use systems.

Soil Gaseous Emissions and Partial C and N Balances of Small-Scale Farmer Fields in a River Oasis of Western Mongolia

“…Compared with studies applying a similar method for capturing soil gaseous emissions, CO 2 -C, N 2 O-N, and NH 3 -N were within the range of reported values for irrigated farmland under arid and semi-arid climate conditions (27 CO [10,11,20]. Thereby, CO 2 -C emission maxima were up to 2.5 times lower than those of intensively managed peri-urban gardens in Niamey, Niger [10] and organic vegetable production systems of the coastal lowlands of Oman [11], but comparable to values measured in small-scaled low input systems in the Nuba Mountains of Sudan [20]. However, maximum N emissions rates were up to 23 times (N 2 O-N) and five times (NH 3 -N) lower in Bulgan sum center compared with values in the previously mentioned studies.…”

“…CO 2 -C, N 2 O-N, and NH 3 -N emissions were measured by a dynamic closed chamber system. The portable system consisted of a polytetrafluoroethylene (PTFE) coated cylindrical polyvinyl chloride (PVC) chamber (0.11-m height and 0.30-m diameter), which was connected with a photoacoustic multi-gas monitor (INNOVA 1312-5, LumaSense Technologies A/S, Ballerup, Denmark) through two 1-m long inlet and outlet PTFE tubes [20]. The outside of the chamber was covered with a layer of aluminum to diminish irradiation-derived temperature increases in the interior.…”

“…Data were collected during the coolest (between 05:00-08:00) and hottest (between 13:00-15:00) daytime to take diurnal variations of soil temperature and soil moisture into account, which both effect gaseous emissions [37]. The emission rates have been computed by dividing the difference in gas concentrations between the first and the 123rd second (data record every 61 seconds) of the measurement period by the elapsed time span of 122 seconds [20]. In rare cases of negative NH 3 and N 2 O emission rates, values were set to zero [20].…”

“…The emission rates have been computed by dividing the difference in gas concentrations between the first and the 123rd second (data record every 61 seconds) of the measurement period by the elapsed time span of 122 seconds [20]. In rare cases of negative NH 3 and N 2 O emission rates, values were set to zero [20]. A linear increase of gas concentrations in the chamber was assumed [38], which was supported by strong bivariate Pearson correlations between gas concentration and accumulation time [39].…”

“…Besides increasing the statistical power [13] and avoiding the negative effects of long chamber closure time on gas diffusion and microclimate [14,15], this would address the observed high spatial heterogeneity and variability of soil properties in the floodplain [16]. A dynamic closed chamber system that is connected to a portable photoacoustic multi-gas monitor [17,18] meets these requirements and had previously shown its suitability for soil emission measurements in remote areas [19][20][21]. However, the accuracy and precision of (particularly N 2 O) measurements made by the photoacoustic monitor were the subject of earlier discussions [22,23] and should be considered during the interpretation of study results.…”