Nitrogen leaching and indirect nitrous oxide emissions from fertilized croplands in Zimbabwe

Agricultural efforts to end hunger in Africa are hampered by low fertilizer-use-efficiency exposing applied nutrients to losses. This constitutes economic losses and environmental concerns related to leaching and greenhouse gas emissions. The effects of NH4NO3 (0, 60 and 120 kg N ha-1) on N uptake, N-leaching and indirect N2O emissions were studied during three maize (Zea mays L.) cropping seasons on clay (Chromic luvisol) and sandy loam (Haplic lixisol) soils in Zimbabwe. Leaching was measured using lysimeters, while indirect N2O emissions were calculated from leached N using the emission factor methodology. Results showed accelerated N-leaching (3–26 kg ha-1 season-1) and N-uptake (10–92 kg ha-1) with N input. Leached N in groundwater had potential to produce emission increments of 0–94 g N2O-N ha-1 season-1 on clay soil, and 5–133 g N2ON ha-1 season-1 on sandy loam soil following the application of NH4NO3. In view of this short-term response intensive cropping using relatively high N rate may be more appropriate for maize in areas whose soils and climatic conditions are similar to those investigated in this study, compared with using lower N rates or no N over relatively larger areas to attain a targeted food security level

Closing maize yield gaps in sub-Saharan Africa will boost soil N2_{2}O emissions

In sub-Saharan Africa (SSA), the most important staple crop is maize; the production of which is dominated by smallholder farming systems using low external inputs (<10 kg N ha$^{−1}$) resulting in low crop yields and large yield gaps (difference between actual and potential yields). To assess increases in soil N$_{2}$O emissions when closing maize yield gaps by increased fertilizer use, we reviewed the literature, developed a relationship between yield gaps and soil N$_{2}$O emissions, and used it to scale across SSA. According to our analysis, N$_{2}$O emissions from maize production will increase from currently 255 to 1755 ± 226 Gg N$_{2}$O-N year$^{−1}$ (+589%) if existing maize yield gaps are closed by 75%, increasing total anthropogenic N$_{2}$O emissions for SSA by c. 50%

GREENHOUSE GAS EMISSIONS FROM SAVANNA (MIOMBO) WOODLANDS: RESPONSES TO CLEARING AND CROPPING

Natural vegetation represents an important sink for greenhouse gases (GHGs); however, there is relatively little information available on emissions from southern African savannas. The effects of clearing savanna woodlands for crop production on soil fluxes of N2 O, CO2 and CH4 were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in Zimbabwe. Maize ( Zea mays L.) was the test crop. Gas samples were measured from undisturbed, cleared and cultivated woodlands using the static chamber methodology involving gas chromatography for ample air analysis. Site and climatic variables were particularly important determinants of GHG emissions. Over an average of 154 days emissions of O.8 \u2013 2.5 kg N2O-N ha-1, 1146 \u2013 2847 kg CO2-C ha-1 and 7.4 \u2013 38.5 kg CH4-C ha-1 were estimated during a season that followed a relatively drier one. Fertiliser-N significantly increased GHG emissions on cropped plots (clay soil). The undisturbed woodland with a relatively higher tree density (loamy sand) was an important GHG source. The high CH4 fluxes from woodlands provide ground based validation of satellite observations of CH4 hotspots in sub-Saharan Africa, and have considerable implications on regional GHG balance.La v\ue9g\ue9tation naturelle repr\ue9sente une source importante de gaz \ue0 effet de serre (GES) ; Par ailleurs, il existe relativement peu d\u2019informations disponibles sur les \ue9missions dans les savanes sud africaines. Les effets du d\ue9boisement de la savane pour la production agricole sur le flux du sol de N2O, CO2 et de CH4 ont \ue9t\ue9 \ue9tudi\ue9s sur les sols argileux (luvisol chromique) et sablo limoneux (acrisol ferrique) au Zimbabwe. La plante test consid\ue9r\ue9e \ue9tait ma\uefs ( Zea mays L.). Des \ue9chantillons de gaz \ue9taient collect\ue9s des for\ueats non perturb\ue9es, d\ue9frich\ue9es et cultiv\ue9es en utilisant la m\ue9thode de la Chambre statique impliquant le gaz chromatographie pour l\u2019analyse de l\u2019air. Le site et les variables climatiques \ue9taient particuli\ue8rement des d\ue9terminants importants des \ue9missions de gaz \ue0 effets de serre. Sur une moyenne de 154 jours des \ue9missions de O.8 \u2013 2.5 kg N2O-N ha-1, 1146 \u2013 2847 kg CO2 -C ha-1 et 7.4 \u2013 38.5 kg CH4-C ha-1 \ue9taient estim\ue9es au cours d\u2019une saison qui a suivi celle relativement la plus s\ue8che. L\u2019engrais N significativement augment\ue9 les \ue9missions de gaz \ue0 effets de serre sur les parcelles cultiv\ue9es (sol argileux). Le sol (sablo-limoneux) sous for\ueats non perturb\ue9es avec relativement une plus grande densit\ue9 d\u2019arbres \ue9tait une source importante de gaz \ue0 effets de serre. Les flux \ue9lev\ue9s de CH4 en condition de v\ue9g\ue9tation naturelle fournit une base de validation des observations satellitaires du CH4 en Afrique subsaharienne, et ont une des implications sur la balance r\ue9gionale des gaz \ue0 effets de serre

Short-term responses of selected soil properties to clearing and cropping of miombo woodlands in central Zimbabwe

Clearing and cultivation of indigenous woodlands for agriculture may be among the most important mechanisms of physical, chemical and biological land degradation in Zimbabwe, and southern Africa in general. The objective of the study was to determine the effects of clearing miombo woodland and converting the land to maize (Zea mays L.) cropping on selected soil properties on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in central Zimbabwe. Soil samples were collected from undisturbed, cleared and cultivated woodlands after four cropping seasons and analyzed for soil organic C, total N and P, exchangeable bases, cation exchange capacity, infiltration rate, aggregate stability and microbial biomass C and N at 0–5, 6–10 and 11–20 cm depths. Results showed that clearing and conversion of miombo woodlands to croplands reduced soil nutrients, cation exchange capacity (range: 9.6–21.0 cmolc kg−1 in clay; 7.0–15.5 cmolc kg−1 in loamy sand), and microbial C (range: 0.06–0.54% in clay; 0.02–0.37% in loamy sand). The extent and nature of change was variable, depending on the soil type and depth. Clearing of trees and leaving soil surface covered with grass did not always translate to a significant decline in soil organic C after four seasons (range: 0.69–2.24% in clay; 0.24–1.43% in loamy sand), unless the clearing was followed by successive cultivation and cropping without N fertilization. The reduced soil quality under cultivation was attributed to a potential pulse in decomposition and mineralization processes caused by soil disturbance, followed by leaching of released nutrients to lower horizons. This could be aided by nutrient removal in crop parts during harvest, without adequate soil nutrient replenishment. Under the woodland ecosystem, litter-fall may help to maintain steady-state infiltration rate (range: 45–126 cm h−1 in clay; 32–97 cm h−1 in loamy sand) by protecting the soil surface from damage and ensuring the formation of stable aggregates which preserve pore continuity. It was recommended that when miombo woodlands are to be cleared, management decisions that reduce tillage intensity and maximize residue retention should be put into practice; otherwise the clearing is strongly discouraged

Greenhouse gas emissions from savanna (miombo) woodlands. Responses to clearing and cropping

ABSTRACT Natural vegetation represents an important sink for greenhouse gases (GHGs); however, there is relatively little information available on emissions from southern African savannas. The effects of clearing savanna woodlands for crop production on soil fluxes of N 2 O, CO 2 and CH 4 were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in Zimbabwe. Maize (Zea mays L.) was the test crop. Gas samples were measured from undisturbed, cleared and cultivated woodlands using the static chamber methodology involving gas chromatography for ample air analysis. Site and climatic variables were particularly important determinants of GHG emissions. Over an average of 154 days emissions of 0.8 -2.5 kg N 2 O-N ha -1 , 1146 -2847 kg CO 2 -C ha -1 and 7.4 -38.5 kg CH 4 -C ha -1 were estimated during a season that followed a relatively drier one. Fertiliser-N significantly increased GHG emissions on cropped plots (clay soil). The undisturbed woodland with a relatively higher tree density (loamy sand) was an important GHG source. The high CH 4 fluxes from woodlands provide ground based validation of satellite observations of CH 4 hotspots in sub-Saharan Africa, and have considerable implications on regional GHG balance. Key Words: Carbon dioxide, methane, nitrous oxide, Zimbabwe RÉSUMÉ La végétation naturelle représente une source importante de gaz à effet de serre (GES) ; Par ailleurs, il existe relativement peu d&apos;informations disponibles sur les émissions dans les savanes sud africaines. Les effets du déboisement de la savane pour la production agricole sur le flux du sol de N 2 O, CO 2 et de CH 4 ont été étudiés sur les sols argileux (luvisol chromique) et sablo limoneux (acrisol ferrique) au Zimbabwe. La plante test considérée était maïs (Zea mays L.). Des échantillons de gaz étaient collectés des forêts non perturbées, défrichées et cultivées en utilisant la méthode de la Chambre statique impliquant le gaz chromatographie pour l&apos;analyse de l&apos;air. Le site et les variables climatiques étaient particulièrement des déterminants importants des émissions de gaz à effets de serre. Sur une moyenne de 154 jours des émissions de 0.8 -2.5 kg N 2 O-N ha -1 , 1146 -2847 kg CO 2 -C ha -1 et 7.4 -38.5 kg CH 4 -C ha -1 étaient estimées au cours d&apos;une saison qui a suivi celle relativement la plus sèche. L&apos;engrais N significativement augmenté les émissions de gaz à effets de serre sur les parcelles cultivées (sol argileux). Le sol (sablo-limoneux) sous forêts non perturbées avec relativement une plus grande densité d&apos;arbres était une source importante de gaz à effets de serre. Les flux élevés de CH 4 en condition de végétation naturelle fournit une base de validation des observations satellitaires du CH 4 en Afrique subsaharienne, et ont une des implications sur la balance régionale des gaz à effets de serre

LAND-USE AND LAND-USE CHANGE EFFECTS ON NITROUS OXIDE EMISSIONS IN THE SEASONALLY DRY ECOSYSTEMS OF ZIMBABWE: A REVIEW

Nitrous oxide (N2O) is a greenhouse gas (GHG) with a considerable warming potential and involvement in the destruction of stratospheric ozone. The conversion of savannas to agricultural land has the potential of changing the characteristics and gas exchange of the ecosystems dramatically. The savanna woodlands cover over 95% of Zimbabwe\u2019s forest area, and are divided into five woodland types: Acacia, miombo, mopane, teak Baikiaea Plurijuga and Terminalia Combretaceae . This review is aimed at exploring the effects of land-use changes and land management practices on N2O emissions in Zimbabwe. Available data on N2O emission were collected from standing and deforested miombo woodlands, grasslands and agricultural lands. Estimated mean annual N2O emissions from savanna ecosystems in Zimbabwe were 17.1 Gg N2O, while annual fluxes from arable land (cultivated and fallow) was 3.19 Gg N2O. Biogenic N2O emissions were mainly concentrated in the wet season as N2O production is strongly enhanced by high soil moisture. During the dry season pyrogenic emissions were also important sources of N2O, contributing, an estimated 6.7 Gg N2O annually. Land use change in the form of biomass burning and conversion to grassland or arable land may be considerable source of N2O, whereas current agricultural practices do not seem to provide a large source of N2O in Zimbabwe. Seasonally dry savanna ecosystems, thus, constitute an important source of N2O, which should not be ignored in national and regional estimates of emissions of N2O. Land-use change from savanna to agricultural production results in an immediate increase in N2O emissions. However, the emissions will decrease with time. The current estimates are associated with large uncertainties, thus, there is need for more detailed studies on the effects of land-use change on N2O emissions and on spatial and temporal variations in N2O emissions from the different savanna ecosystems.L\u2019oxyde nitreux (N2O) est un gaz \ue0 effet de serre (GES) avec un potentiel de r\ue9chauffement et une implication dans la destruction de la couche stratosph\ue9rique d\u2019ozone. La conversion des savanes en terres agricoles induit le changement radicales des caract\ue9ristiques et \ue9changes gazeux des \ue9cosyst\ue8mes. Les savanes bois\ue9es couvrent plus de 95% de la couverture foresti\ue8re au Zimbabwe et sont subdivis\ue9es en cinq types de boisements : Acacia, miombo, mopane, teak ( Baikiaea Plurijuga ) et Terminalia Combretaceae . Cet article visait \ue0 examiner la contri- bution potentielle des \ue9cosyst\ue8mes \ue0 savanes non perturb\ue9es et les effets des changements dans l\u2019utilisation des terres sur les \ue9missions de N2O. Les donn\ue9es disponibles sur les \ue9missions de N2O \ue9taient collect\ue9es des r\ue9gions bois\ue9es de Miombo, r\ue9gions de bois\ue9es de miombo, les prairies et des terres agricoles. La moyenne des flux de N2O des \ue9cosyst\ue8mes \ue0 savane estim\ue9e \ue0 17.1Gg pendant que les flux annuels \ue0 partir des terres arables (cultiv\ue9es et en jach\ue8re) \ue9tait de 13.9Gg. Les flux \ue9taient principalement concentr\ue9s dans la saison humide du fait que les \ue9missions de N2O sont fortement influenc\ue9es par l\u2019humidit\ue9 \ue9lev\ue9e du sol. Les \ue9missions pyrog\ue9niques de la saison s\ue8che constituaient d\u2019importantes sources de N2O, avec un niveau annuel d\u2019\ue9mission de 6.7Gg. Les \ue9cosyst\ue8mes de savane en saison s\ue8che constituent ainsi une importante source de N2O \ue0 ne pas n\ue9gliger dans des estimations nationales et r\ue9gionales des \ue9missions de gaz. Les estimations actuelles sont associ\ue9es \ue0 de grandes incertitudes, ainsi, la n\ue9cessit\ue9 d\u2019\ue9tudes plus d\ue9taill\ue9es sur les variations spatiales et temporelles des \ue9missions produites dans diff\ue9rents \ue9cosyst\ue8mes \ue0 savane, et les effets du changement dans l\u2019utilisation des terres sur les \ue9missions de N2O

Land-use and land-use change effects on nitrous oxide emissions in the seasonally dry ecosystems of Zimbabwe: A review

Nitrous oxide (N2O) is a greenhouse gas (GHG) with a considerable warming potential and involvement in the destruction of stratospheric ozone. The conversion of savannas to agricultural land has the potential of changing the characteristics and gas exchange of the ecosystems dramatically. The savanna woodlands cover over 95% of Zimbabwe’s forest area, and are divided into five woodland types: Acacia, miombo, mopane, teak (Baikiaea Plurijuga) and Terminalia-Combretaceae. This review is aimed at exploring the effects of land-use changes and land management practices on N2O emissions in Zimbabwe. Available data on N2O emission were collected from standing and deforested miombo woodlands, grasslands and agricultural lands. Estimated mean annual N2O emissions from savanna ecosystems in Zimbabwe were 17.1 Gg N2O, while annual fluxes from arable land (cultivated and fallow) was 3.19 Gg N2O. Biogenic N2O emissions were mainly concentrated in the wet season as N2O production is strongly enhanced by high soil moisture. During the dry season pyrogenic emissions were also important sources of N2O, contributing, an estimated 6.7 Gg N2O annually. Land use change in the form of biomass burning and conversion to grassland or arable land may be considerable source of N2O, whereas current agricultural practices do not seem to provide a large source of N2O in Zimbabwe. Seasonally dry savanna ecosystems, thus, constitute an important source of N2O, which should not be ignored in national and regional estimates of emissions of N2O. Land-use change from savanna to agricultural production results in an immediate increase in N2O emissions. However, the emissions will decrease with time. The current estimates are associated with large uncertainties, thus, there is need for more detailed studies on the effects of land-use change on N2O emissions and on spatial and temporal variations in N2O emissions from the different savanna ecosystems

Balancing co-benefits and trade-offs between climate change mitigation and adaptation innovations under mixed crop-livestock systems in semi-arid Zimbabwe

Achieving Zimbabwe’s national and international commitments to food systems transformation and climate resilience building is of high priority. Integrated simulation-based research approaches developed under the Agricultural Model Intercomparison and Improvement Project (AgMIP) are important sources of evidence to guide policy decisions towards sustainable intensification. Through the identification of economically viable, socially inclusive and environmentally sustainable development pathways, the analysis in this study evaluates co-benefits and tradeoffs between climate change adaptation and mitigation interventions for vulnerable smallholder crop-livestock holdings in the semi-arid regions of Zimbabwe. We explore how climate effects disrupt the livelihoods and food security for diverse farm types, the extremely vulnerable and those better resource endowed but facing high risks. In an iterative process with experts and stakeholders, we co-developed context specific development pathways. They include market-oriented adaptation and mitigation interventions and social protection mechanisms that would support the transition towards more sustainable intensified, diversified and better integrated crop-livestock systems. We assess the trade-offs associated with adoption of climate-smart interventions aimed at improving incomes and food security but that may have consequences on GHG emissions for the different pathways and farm types. The approach and results inform the discussion on drivers that can bring about sustainable intensification, and the extent to which socio-economic benefits could enhance the uptake of emission reducing technologies thereof. Through this strategy we evaluate interventions that can result in win–win outcomes, that is, adaptation-mitigation co-benefits, and what this would imply for policies that aim at transforming agri-food systems

Nitrous oxide emissions from European agriculture - An analysis of variability and drivers of emissions from field experiments

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 (<i>p</i> < 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