Optimizing a three-way pact comprising crop yields, fertility inputs and greenhouse gases may minimize the contribution of croplands to global warming. Fluxes of N 2 O, CO 2 and CH 4 from soil were measured under maize (Zea mays L.) grown using 0, 60 and 120 kg N hm -2 as NH 4 NO 3 -N and composted manure-N in three seasons on clay (Chromic luvisol) and sandy loam (Haplic lixisol) soils in Zimbabwe. The fluxes were measured using the static chamber methodology involving gas chromatography for ample air analysis. Over an average of 122 days we estimated emissions of 0.1 to 0.5 kg N 2 O-N hm −2 , 711 to 1574 kg CO 2 -C hm −2 and−2.6 to 5.8 kg CH 4 -C hm −2 from six treatments during season II with the highest fluxes. The posed hypothesis that composted manure-N may be better placed as a mitigation option against soil emissions of GHG than mineral fertilizer-N was largely supported by N 2 O fluxes during the wet period of the year, but with high level of uncertainty. Nitrogen addition might have stimulated both emissions and consumption of CH 4 but the sink or source strength depended highly on soil water content. We concluded that the application of mineral-N and manure input may play an important role with reference to global warming provided the season can support substantial crop productivity that may reduce the amount of N 2 O loss per unit yield. Confidence in fluxes response to agricultural management is still low due to sporadic measurements and limited observations from the southern African region.
Abstract. Nitrous oxide emissions from a network of agricultural experiments in Europe were used to explore the relative importance of site and management controls of emissions. At each site, a selection of management interventions were compared within replicated experimental designs in plot-based experiments. Arable experiments were conducted at Beano in Italy, El Encin in Spain, Foulum in Denmark, Logården in Sweden, Maulde in Belgium, Paulinenaue in Germany, and Tulloch in the UK. Grassland experiments were conducted at Crichton, Nafferton and Peaknaze in the UK, Gödöllö in Hungary, Rzecin in Poland, Zarnekow in Germany and Theix in France. Nitrous oxide emissions were measured at each site over a period of at least two years using static chambers. Emissions varied widely between sites and as a result of manipulation treatments. Average site emissions (throughout the study period) varied between 0.04 and 21.21 kg N2O-N ha−1 yr−1, with the largest fluxes and variability associated with the grassland sites. Total nitrogen addition was found to be the single most important determinant of emissions, accounting for 15% of the variance (using linear regression) in the data from the arable sites (p < 0.0001), and 77% in the grassland sites. The annual emissions from arable sites were significantly greater than those that would be predicted by IPCC default emission factors. Variability of N2O emissions within sites that occurred as a result of manipulation treatments was greater than that resulting from site-to-site and year-to-year variation, highlighting the importance of management interventions in contributing to greenhouse gas mitigation.
Land used for agricultural production can contribute significantly to greenhouse gas (GHG) emissions; however, there is very little information on the role of management and land use change in influencing these emissions in Africa. Thus, exploring GHG emissions that occur at the soil-atmosphere interface is an essential part of the effort to integrate land management strategies with climate change mitigation and adaptation in southern Africa. We measured soil emissions of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) from rain-fed perennial tropical grassland, wastewater-irrigated perennial tropical pastureland, recently cleared woodland, miombo woodland, a Eucalyptus plantation, regular cropland and recently cleared-and-cropped land, on two contrasting soils at five sites in one cropping season in Zimbabwe. Gas samples were collected using static chambers and analysed by gas chromatography. Considerably high GHG emissions were found on sewage effluent-irrigated pastureland (means, 190 mg CO 2 -C m −2 hour −1 , 102 μg CH 4 -C m −2 hour −1 and 6 μg N 2 O-N m −2 hour −1 from sandy soil) and altered woodlands (mean ranges, 38-70 CO 2 -C m −2 hour −1 , 12-43 μg CH 4 -C m −2 hour −1 and 20-31 μg N 2 O-N m −2 hour −1 from deforested and cultivated woodland on clay and sandy soils). Relatively low and less variable emissions were found among the rain-fed perennial tropical grasslands, regular croplands and Eucalyptus plantations (mean ranges, 19-39 mg CO 2 -C m −2 hour −1 , −9.4-2.6 μg CH 4 -C m −2 hour −1 and 1.0-4.7 μg N 2 O-N m −2 hour −1 ). Variability in CO 2 , CH 4 and N 2 O emissions from soils was to the greatest extent influenced by soil temperature, but soil moisture, mineral-N and pH were also important. The increased N 2 O emissions from cleared woodland on clay soil were attributed to increased mineralization and N availability when no tree could take up that N, while the N mineralized on the sandy soil could have been largely leached due to the soil's poor nutrient holding capacity, resulting in a relatively lower N 2 O emission response to clearing. We concluded that the alteration of woodlands by deforestation and cultivation increased soil temperature, resulting in increased soil respiration, while the establishment of Eucalyptus plantations may provide an option for reduction in soil emissions of CO 2 and N 2 O and a sink for CH 4 .
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