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.

Climate change has resulted in increased vulnerability of smallholder farmers in marginal areas of Zimbabwe where there is limited capacity to adapt to changing climate. One approach that has been used to adapt to changing climate is in-field water harvesting for improved crop yields in the semi- arid regions of Zimbabwe. This review analyses the history of soil and water conservation in Zimbabwe, efforts of improving water harvesting in the post independence era, farmer driven innovations, water harvesting technologies from other regions, and future directions of water harvesting in semi arid marginal areas. From this review it was observed that the blanket recommendations that were made on the early conservation method were not suitable for marginal areas as they resulted in increased losses of the much needed water. In the late 1960 and 70s’, soil and water conservation efforts was a victim of the political environment and this resulted in poor uptake. Most of the water harvesting innovations which were promoted in the 1990s’ and some farmer driven innovations improved crop yields in marginal areas but were poorly taken up by farmers because they are labour intensive as the structures should be made annually. To address the challenges of labour shortages, the use of permanent in-field water harvesting technologies are an option. There is also need to identify ways for promoting water harvesting techniques that have been proven to work and to explore farmer-led knowledge sharing platforms for scaling up proven technologies.

Aim We test the hypothesis that land use and climate are important controls of nitrous oxide (N 2 O) emissions from savanna ecosystems, and that these emissions can be represented by a mechanistic model of carbon (C) and nitrogen (N) transformations.Location Miombo woodlands in Zimbabwe are part of widespread woody savanna formations in southern and central Africa that cover more than 2.7 million km 2 . The rainfall in this region is around 800 mm and is concentrated in the period between November and March.Methods Losses of N 2 O were measured along transects in two field areas using static chambers over a period of 1 year. The vegetation in both areas was dominated by Julbernardia globiflora and Brachystegia spiciformis, but had differing management systems (burned and unburned), soil properties and site characteristics (slope and drainage). The effects of simulated rainfall and fertilizer additions were studied in laboratory incubations.Results Patterns of N 2 O emissions were strongly linked to rainfall. The highest fluxes at both sites were measured within 18 days of the onset of the first rains in November, with fluxes of up to 42 lg N m )2 h )1 . During the dry season, fluxes were lower, but a large proportion (R 2 values between 0.8 and 0.95, P < 0.001) of the N 2 O flux could be predicted by variations in soil moisture. Soil columns were set up in the laboratory to which simulated rainwater was added, and the amounts and timing of rainwater addition were varied. Losses of N 2 O were highest within the first week of the laboratory study. Altering the amount of rainwater addition did not significantly affect N 2 O loss; however, a continuous addition of water resulted in higher losses of N 2 O (up to 79 lg N m )2 h )1 ) than periodic addition of the same amount. A model (denitrification-decomposition) was used to simulate N 2 O release over a 12 month period, using meteorological data recorded in the vicinity of the field site. The simulations and field data suggest that nitrification was the main process responsible for N 2 O release during the dry season but that denitrification was more important during the wet season.Main conclusions The release of N 2 O from dryland savannas was shown to constitute an important nutrient flux, and emissions were strongly linked to patterns of rainfall; however, there was evidence to suggest that the magnitude of fluxes is also influenced locally by differences in soil organic matter concentration and drainage.

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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.