Limits of agricultural greenhouse gas calculators to predict soil N2O and CH4 fluxes in tropical agriculture

Acknowledgements This work was undertaken as part of the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), which is a strategic partnership of CGIAR and Future Earth. This research was carried out with funding by the European Union (EU) and with technical support from the International Fund for Agricultural Development (IFAD). The UN FAO Mitigation of Climate Change in Agriculture (MICCA) Programme funded data collection in Kenya and Tanzania. The views expressed in the document cannot be taken to reflect the official opinions of CGIAR, Future Earth, or donors. We thank Louis Bockel of the UN FAO Agricultural Development Economics Division (ESA) for his comments on an earlier draft of the manuscript.Peer reviewedPublisher PD

Limits of agricultural greenhouse gas calculators to predict soil N\u3csub\u3e2\u3c/sub\u3eO and CH\u3csub\u3e4\u3c/sub\u3e fluxes in tropical agriculture

Demand for tools to rapidly assess greenhouse gas impacts from policy and technological change in the agricultural sector has catalyzed the development of \u27 GHG calculators\u27-simple accounting approaches that use a mix of emission factors and empirical models to calculate GHG emissions with minimal input data. GHG calculators, however, rely on models calibrated from measurements conducted overwhelmingly under temperate, developed country conditions. Here we show that GHG calculators may poorly estimate emissions in tropical developing countries by comparing calculator predictions against measurements from Africa, Asia, and Latin America. Estimates based on GHG calculators were greater than measurements in 70% of the cases, exceeding twice the measured flux nearly half the time. For 41% of the comparisons, calculators incorrectly predicted whether emissions would increase or decrease with a change in management. These results raise concerns about applying GHG calculators to tropical farming systems and emphasize the need to broaden the scope of the underlying data

Independent and combined effects of improved water, sanitation, and hygiene, and improved complementary feeding, on child stunting and anaemia in rural Zimbabwe: a cluster-randomised trial.

BACKGROUND: Child stunting reduces survival and impairs neurodevelopment. We tested the independent and combined effects of improved water, sanitation, and hygiene (WASH), and improved infant and young child feeding (IYCF) on stunting and anaemia in in Zimbabwe. METHODS: We did a cluster-randomised, community-based, 2 × 2 factorial trial in two rural districts in Zimbabwe. Clusters were defined as the catchment area of between one and four village health workers employed by the Zimbabwe Ministry of Health and Child Care. Women were eligible for inclusion if they permanently lived in clusters and were confirmed pregnant. Clusters were randomly assigned (1:1:1:1) to standard of care (52 clusters), IYCF (20 g of a small-quantity lipid-based nutrient supplement per day from age 6 to 18 months plus complementary feeding counselling; 53 clusters), WASH (construction of a ventilated improved pit latrine, provision of two handwashing stations, liquid soap, chlorine, and play space plus hygiene counselling; 53 clusters), or IYCF plus WASH (53 clusters). A constrained randomisation technique was used to achieve balance across the groups for 14 variables related to geography, demography, water access, and community-level sanitation coverage. Masking of participants and fieldworkers was not possible. The primary outcomes were infant length-for-age Z score and haemoglobin concentrations at 18 months of age among children born to mothers who were HIV negative during pregnancy. These outcomes were analysed in the intention-to-treat population. We estimated the effects of the interventions by comparing the two IYCF groups with the two non-IYCF groups and the two WASH groups with the two non-WASH groups, except for outcomes that had an important statistical interaction between the interventions. This trial is registered with ClinicalTrials.gov, number NCT01824940. FINDINGS: Between Nov 22, 2012, and March 27, 2015, 5280 pregnant women were enrolled from 211 clusters. 3686 children born to HIV-negative mothers were assessed at age 18 months (884 in the standard of care group from 52 clusters, 893 in the IYCF group from 53 clusters, 918 in the WASH group from 53 clusters, and 991 in the IYCF plus WASH group from 51 clusters). In the IYCF intervention groups, the mean length-for-age Z score was 0·16 (95% CI 0·08-0·23) higher and the mean haemoglobin concentration was 2·03 g/L (1·28-2·79) higher than those in the non-IYCF intervention groups. The IYCF intervention reduced the number of stunted children from 620 (35%) of 1792 to 514 (27%) of 1879, and the number of children with anaemia from 245 (13·9%) of 1759 to 193 (10·5%) of 1845. The WASH intervention had no effect on either primary outcome. Neither intervention reduced the prevalence of diarrhoea at 12 or 18 months. No trial-related serious adverse events, and only three trial-related adverse events, were reported. INTERPRETATION: Household-level elementary WASH interventions implemented in rural areas in low-income countries are unlikely to reduce stunting or anaemia and might not reduce diarrhoea. Implementation of these WASH interventions in combination with IYCF interventions is unlikely to reduce stunting or anaemia more than implementation of IYCF alone. FUNDING: Bill & Melinda Gates Foundation, UK Department for International Development, Wellcome Trust, Swiss Development Cooperation, UNICEF, and US National Institutes of Health.The SHINE trial is funded by the Bill & Melinda Gates Foundation (OPP1021542 and OPP113707); UK Department for International Development; Wellcome Trust, UK (093768/Z/10/Z, 108065/Z/15/Z and 203905/Z/16/Z); Swiss Agency for Development and Cooperation; US National Institutes of Health (2R01HD060338-06); and UNICEF (PCA-2017-0002)

The Effects of Improved Fallows and Tillage Management on Soil and Water Conservation in a Sandy Soil.

Research on improved fallows has concentrated on soil fertility benefits neglecting possible benefits to soil and water conservation. The objective of this study was to determine changes in infiltration rates, water and nutrient losses, hydraulic conductivity, soil porosity, water retention, aggregate stability and maize yields during the cropping phase in a maize-fallow rotation, under conventional tillage (CT) and no tillage (NT). The study was carried out on plots where a 2-year planted fallow-maize rotation was practiced since 1992/93 cropping season. Soil and water conservation were investigated using simulated rainfall at an intensity of 35 mm h–1, infiltration rates were measured using double rings and hydraulic conductivity and porosity were measured using a tension infiltrometer. Soil samples for the measurement of soil water retention and aggregate stability were collected and measurements were done in the laboratory. Treatments evaluated were planted fallows of Acacia angustissima (A. angustissima) and Sesbania sesban (S. sesban),, natural fallow (NF) and continuous maize (Zea Maize). Improved fallows resulted in significantly higher (P35 mm h–1. Two years after fallow termination (October 2002) steady state infiltration rates averaged 21, 14 and 5 mm h–1, for NF, S. sesban and continuous maize. Runoff losses from the same simulation measurements were significantly lower (P<0.05) in fallows than in continuous maize. These losses were 44% in continuous maize compared to 22% in S. sesban and none in A. angustissima and NF plots after 30 minutes at fallow termination (October 2000). After one year, the average runoff loss across conventionally and NT plots increased to 57% for continuous maize, 30% for S. sesban and no losses for A. angustissima and NF. In October 2002, runoff losses were 63%, 61% and 45% for continuous maize, S. sesban and NF. In A angustissima there were no runoff losses throughout the of study. Aggregate stability using the water stable aggregation method, the macroaggregation index (Ima) was 550, 480, 450 and 300 for NF, A. anguistissima, S. sesban and continuous maize respectively. In October 2002 Ima in CT plots had decreased to 270, 390 and 260 in for NF, A. angustissima and S. sesban respectively. Ima in NT plots also decreased to 290, 450 and 270 for NF, A. angustissima and S. sesban respectively. There were no changes in Ima in continuous maize for either tillage systems. Cumulative kinetic energy required to rapture aggregates also declined from 859, 568 and 395 joules g-1 of aggregate at fallow termination (October 2000) to 231, 395 and 236 for NF, A. angustissima and S. sesban respectively for CT plots and 372, 491 and 268 joules g-1 of aggregate for NT plots two years after fallow termination. There were no changes in the amount of energy required to break aggregates in continuous maize, ranging from 80-100 joules g-1 of aggregate over the two-year period. Using the different assessment methods, aggregate stability was significantly higher (P<0.05) in fallows relative to continuous maize. No till resulted in significantly (P<0.05) more stable aggregates than CT. Improved fallowing also resulted in significantly higher (P<0.05) soil water retention, hydraulic conductivity and an increase in the proportion of larger pore sizes one year after fallow termination. Hydraulic conductivity at 5 cm tension was between 0.7 and 0.9 cm h-1, in improved fallows relative to 0.5 cm h-1 in continuous maize. Pores were significantly higher (P <0.05) in fallows. At 5cm tension the number of pores m-2 varied from 285-443, whilst in continuous maize they were less than 256 pores m-2. At 10cm tension the number of pores m-2 varied from 4500-8900 in fallows relative to 3900 pores m-2 in continuous maize. There were no significant tillage effects (P<0.05) on water retention, hydraulic conductivity and porosity. Maize yields were significantly higher (P<0.05) in improved fallows than in continuous maize and NF for both 2001 and 2002. In 2001 maize yields were 1.8, 1.2, 0.7 and 0.5 t ha-1 for A. angustissima, continuous maize, S. sesban and NF respectively under CT. Under NT yields were 1.3, 0.8, 0.7 and 0.2 t ha-1 for A. angustissima, continuous maize, S. sesban and NF respectively. In 2002 yields under CT were 1.7, 1.3, 1.2 and 0.5 t ha-1 for S. sesban, continuous maize, and NF and A. angustissima respectively. Corresponding yields under NT were 1.5, 0.6, 0.3 and 0.25 for S. sesban, continuous maize, NF and A. angustissima respectively. Generally CT out yielded NT (P<0.05) during both cropping seasons irrespective of fallow treatment. These results showed that fallowing resulted in reduced water and soil losses during the cropping phase compared to continuous maize cropping. Reduced water and soil losses were a result of increased infiltration rates and aggregate stability during fallowing. However these benefits decreased with the introduction of tillage as shown by the decline in infiltration rates and aggregation from fallow termination (October 2000) to October 2002. Therefore fallowing can improve soil and water conservation relative to continuous maize cropping. Among the fallows, A.angustissima and NF had the least soil and water losses, compared to S. sesban. However improved fallows proved superior to NF in maize yields because they fixed nitrogen, which is used during crop growth. The benefits of improved soil physical properties accrued during fallowing did not translate to improved yields in NF because the chemical fertility was more limiting than soil physical properties. This study demonstrated that fallowing improved soil and water conservation thereby emphasising the need for inclusion of improved fallows by farmers in their crop rotations

Greenhouse gas emissions from cultivated dambos from Central Zimbabwe

Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) are potent greenhouse gases (GHGs) which cause climate change. The major anthropogenic sources of these GHGs are industrial production, burning of fossil fuel and agriculture, while the major natural sources include wetlands. However, the contribution of tropical wetlands, particularly seasonal wetlands (dambos) which occupy an estimated 20% of the elevated central African plateau towards GHG emissions are currently unknown as there has been few measurements in the region. Dambos contain large stocks of soil organic carbon (SOC), and they are a potential source of GHGs in their natural state. When dambos are disturbed through practices such as burning, or when vegatation is removed through clipping or clearing and cultivation with the application of both organic and inorganic fertilisers, there is likely to be a change in the SOC and GHG emissions, but currently there is little data on the effect of these various practices on SOC dynamics and GHG emissions. The objective of this study was to quantify SOC and GHG emissions from dambos in their natural state and determine how dambo distubances, and fertiliser application affect SOC and GHG emissions. Soil samples were collected from; a dambo transect, farmers’ gardens, plots that were subjected to different disturbance regimes, and plots that were planted to rape (Brassica napus). Soil organic carbon was determined using Walkely-Black procedure, while GHG emissions were measured using static chambers. Along the transect, the average SOC stocks were 3.3, 4.5, 30,4, 7.2 and 4.4 Mg ha-1 for the upland, margin, mid-slope and bottom catena positions respectively for the 0-40 cm depth. Methane emissions were -0.3, 29.5 and -1.3 mg m-2 hr-1, N2O emissions were 40.1, 3.9, and 5.5 μg m2 hr-1, while CO2 emissions were 2648.9, 896.2, 590.1 mg m-2 hr-1 for upland, mid-slope and bottom catena positions respectively. The average emissions for dambos alone (mid-slope and bottom catena) were 14.6 mg m-2 hr-1 for CH4, 4.7 μg m2 hr-1 for N2O and 744 mg m-2 hr-1 for CO2. Dambo cultivation, clearing and clipping resulted in a 32%, 25 and 16% reduction in dambo SOC, though burning resulted in a 28% increased SOC. Burning significantly (p<0.05) increased CH4 emissions, compared to cultivation, clipping and clearing. Methane emissions were 10.1, 7.0, 7.6, 6.7 and 5.5 mg m-2 hr-1, CO2 emissions were 2541, 3543, 4209, 6081 and 2425 mg m-2 hr-1, while N2O emissions were 30.7, 56.6, 1.8, 23.9 and 57.4 μg m-2 hr-1 for burning, cleared, control, clipping and ploughing respectively. The application of fertilisers in cultivated dambos planted to rape resulted in increased N2O and CO2 emissions. The results showed that the application of cattle manures resulted in N2O emissions that ranged between 218-894 μg m-2 hr-1, while with inorganic N fertilizers N2O emissions ranged from 555 -5186 μg m-2 hr-1. However, for integrated nutrient management, where low amounts of inorganic fertilizers are mixed with cattle manures, N2O emissions ranged from 106 to 2826 μg m-2 hr-1. The use of inorganic fertilisers resulted in higher N2O emissions per kg yield obtained (6-14 g N2O kg-1 yield), when compared to 0.7-4.5 g N2O kg-1 yield and 1.6-4.6 g N2O kg-1 yield for organic manures and for mixtures of organic and inorganic N. Dambos planted to rape were weak sources of CH4 and average annual emissions were between -0.02-0.9 mg m-2 hr-1. It was concluded that dambos exhibit high variability in emissions depending on catenal position along a transect, nature of disturbance and the type of GHG. High inorganic N fertiliser application in cultivated dambos increased N2O emissions, while organic manures and integrated nutrient management resulted in lower emissions and are thus recommended for mitigating GHG emissions in cultivated dambos.,International Foundation of Science (IFS), DAAD Fellowship, Climate Food and Farming (CLIFF) network of the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) and Bindura University of Science Education Block Allocation

Effects of different disturbance regimes on grass and herbaceous plant diversity and biomass in Zimbabwean dambo systems

This study examined the species richness, diversity, biomass of grasses and herbaceous plants and seed germination in plots with contrasting disturbance regimes established in a dambo garden, in Chiota, Zimbabwe. The disturbance regimes were burning, clipping, clearing and conventional tillage and were applied annually to each subplot from 2010 to 2012. It was hypothesised that burning increases biomass, species richness and diversity of plants while reducing seed bank diversity. Clearing, clipping and conventionally tilling negatively affect biomass, species richness and diversity. The Shannon–Wiener Index was used to estimate species diversity and the average values obtained ranged 0.53, 0.85, 0.91, 1.3 and 1.70, for the undisturbed, burnt, conventionally tilled, clipped and cleared plots, respectively. The biomass in the experiment ranged from 0.92t ha–1 for the ploughed plot to 20.92t ha–1 for the undisturbed plot. The species richness for the plants decreased in the following order; clearing>conventional tillage>burning>clipping>undisturbed. These results show that disturbance regimes increased species richness but however decreased plant biomass. It is apparent that the management practice that ensures maximum biomass of grasses and herbs in dambos is maintaining them in their natural state. However, clearing seemed to improve species diversity compared to maintaining the dambo in its natural state.EDITED BY Alexander van Oudenhoven and Patricia Balvaner

Opportunities for optimization of in-field water harvesting to cope with changing climate in semi-arid smallholder farming areas of Zimbabwe

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

Enhancing nitrogen and rainwater use efficiency through rainwater harvesting in semi-arid smallholder sorghum (Sorghum bicolor) farming systems

AbstractNitrogen and rainwater use efficiency in semi-arid smallholder farming systems is low due to low soil fertility and unreliable rainfall. The objective of this study was to evaluate the effect of rainwater harvesting and mineral nitrogen fertilizer on nitrogen and rainwater use efficiency under two sorghum (Sorghum bicolor) varieties. A split-split plot experiment, replicated three times, was conducted in Mt Zonwe smallholder farming area from 2016/17 to 2018/19. The results showed that water content under tied contour (TC) and infiltration pits (IP) had significantly higher water content compared to standard contour (SC) and moisture content significantly decreased with an increase in distance from RWH practices. TC and IP had higher agronomic efficiency than SC across all nitrogen applications, distance from RWH practice, and seasons. Sorghum variety Macia had higher nitrogen use efficiency indices than Sc Sila at nitrogen application of 50 and 70 kg N/ha while nitrogen application >100 kg N/ha had no difference in nitrogen use in both varieties. A decreasing trend in nitrogen productivity with an increase in nitrogen application was shown in both varieties. Mineral nitrogen fertilizer application increased rainwater productivity up to 100 kg N/ha beyond which there was no significant difference. Regardless of sorghum variety and season, TC and IP had higher rainwater use efficiency than SC at each distance from RWH practice. This study recommends the integrated use of TC and IP rainwater harvesting practices and mineral nitrogen fertilizer sustainably to improve N and rainwater productivity in semi-arid smallholder sorghum farming systems

Effect of contour rainwater-harvesting and integrated nutrient management on sorghum grain yield in semi-arid farming environments of Zimbabwe

The application of insufficient amounts of mineral fertiliser, coupled with unreliable precipitation, has caused a drastic reduction in the yield of sorghum in the smallholder-farming areas of Zimbabwe. This calls for innovative interventions to improve production under changing climatic conditions. This study evaluated the effect of contour-based rainwater-harvesting methods and the use of cattle manure + N nutrient amendment on sorghum yield. A split-split plot experiment was conducted where rainwater-harvesting practice, sorghum variety, cattle manure + N and distance from rainwater-harvesting structure were treatment factors. The results showed that the yield of sorghum was significantly higher under the tied contour and infiltration pits than standard contour at all distances from rainwater-harvesting practices and seasons. In all seasons sorghum varieties Macia and Sc Sila showed higher yield under the tied contour and infiltration pits than standard contour. However, regardless of the distance from rainwater-harvesting practice and season the sorghum variety, Macia showed a higher grain yield than Sc Sila. At each incremental level of N application to cattle manure, Macia had a higher grain yield than Sc Sila, and no significant grain yield benefits were shown in each variety at N application to cattle manure above 50 kg N ha−1

The effects of catena positions on greenhouse gas emissions along a seasonal wetland (dambo) transect in tropical Zimbabwe

Wetlands are major natural sources of greenhouse gases (GHGs). In central and southern Africa, one of the most extensive wetlands are dambos (seasonal wetlands) which occupy 20–25% of land area. However, there are very little data on GHG methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) emissions from dambos, and this study presents the first estimates from dambos in Zimbabwe. The objective was to evaluate the effects of catena positions; upland, dambo mid-slope and dambo bottom, on GHG emissions along an undisturbed dambo transect. Methane emissions were −0.3, 29.5 and −1.3 mg m−2 hr−1, N2O emission were 40.1, 3.9 and 5.5 µg m2 hr−1, while CO2 emissions were 2648.9, 896.2 and 590.1 mg m−2 hr−1 for upland, mid-slope and bottom catena, respectively. Our results showed that uplands were important sources of N2O and CO2, and a sink for CH4, while the dambo mid-slope position was a major source of CH4, but a weak source of CO2 and N2O. Dambo bottom catena was weak source GHGs. Overall, dambos were major sources of CH4 and weak sources of N2O and CO2.We concluded that, depending on catenal position, dambos can be major or minor sources of GHGs