Moses M. Tenywa

An evaluation of aerobic and anaerobic composting of banana peels treated with different inoculums for soil nutrient replenishment.

This study sought to evaluate the efficacy of aerobic and anaerobic composting of inoculated banana peels, and assess the agronomic value of banana peel-based compost. Changes in the chemical composition under aerobic and anaerobic conditions were examined for four formulations of banana peel-based wastes over a period of 12 weeks. The formulations i.e. plain banana peel (B), and a mixture with either cow dung (BC), poultry litter (BP) or earthworm (BE) were separately composted under aerobic and anaerobic conditions under laboratory conditions. Inoculation with either cow dung or poultry litter significantly facilitated mineralization in the order: BP>BC>B. The rate of decomposition was significantly faster under aerobic than in anaerobic composting conditions. The final composts contained high K (>100 g kg(-1)) and TN (>2%), indicating high potential as a source of K and N fertilizer.

Managing soils in Sub-Saharan Africa: Challenges and opportunities for soil and water conservation

In this 21st century, agriculture continues to be an important sector for sustainable development and poverty reduction in Sub-Saharan Africa. Research indicates that 1% growth in this sector translates into 2.5% growth in income for the poor people in the region. However, such growth is still low and per capita food production has been insufficient and decreasing over time because it is based on smallholder agriculture that often provides insufficient incentives to use land resources sustainably. Compounding problems include volatility in input prices, markets, and climate, declining farm sizes as a result of rising population pressures, weak extension services, low adoption of improved technologies, and limited government investments. In addition, Sub-Saharan Africa continues to experience destructive extraction, over-exploitation, and inadequate conservation of soil and water. More work needs to be done to demonstrate to policy makers, development partners, and society at large the full contribution that will be made to poverty alleviation by increasing and sustaining agricultural productivity through investments in soil rehabilitation, water harvesting and utilization, and reduction of land degradation. Several success stories of local soil and water conservation activities practiced by farmers in Sub-Saharan Africa exist, but the challenge is to scale these successes to wider implementation.

Aggregate size distribution in a biochar-amended tropical Ultisol under conventional hand-hoe tillage

Highlights • Biochar does not affect soil aggregation on the humid Ultisol within two years.• Biochar, when applied with T. diversifolia, increased soil aggregation.• Mineral fertilizer reduced macro-aggregate stability in the short-term.• SOC increases in the micro-aggregates but reduces in macro-aggregates.

Emissions intensity and carbon stocks of a tropical Ultisol after amendment with Tithonia green manure, urea and biochar

Highlights • Biochar increased CO2 emissions, reduced CH4 soil uptake, and reduced N2O emissions.• N2O decreased the most (42%) where all the three amendments were present.• Decreased in EI with biochar in low fertility soils is mainly through greater net primary productivity.• Biochar alone decreased SOC but increase it when applied together with urea and Tithonia.

CRITICAL SOIL ORGANIC CARBON RANGE FOR OPTIMAL CROP RESPONSE TO MINERAL FERTILISER NITROGEN ON A FERRALSOL

Soil Organic Carbon (SOC) is a major indicator of soil fertility in the tropics and underlies variability in crop response to mineral fertilizers. Critical SOC concentrations that interact positively with N fertilizer for optimal crop yield are less understood. A study was conducted on a Ferralsol in sub-humid Uganda to explore the critical range of SOC concentrations and associated fractions for optimal maize ( Zea mays L.) yield response to applied mineral N fertiliser. Maize grain yield response to N rates applied at 0, 25, 50 and 100 kg N ha −1 in 30 fields of low fertility (SOC 1.2%), medium fertility (SOC = 1.2–1.7%) and high fertility (SOC > 1.7%) was assessed. Soil was physically fractionated into sand-sized (63–2000 µm), silt-sized (2–63 µm) and clay-sized ( 1.2% SOC registered the highest agronomic efficiency (AE) and grain yield. Non-linear regression models predicted critical SOC for optimal yields to be 2.204% at the 50 kg N ha −1 rate. Overall, models predicted 1.9–2.2% SOC as the critical concentration range for high yields. The critical range of SOC concentrations corresponded to 3.5–5.0 g kg −1 sand-sized C and 9–11 g kg −1 for clay-sized C.

Global Boundary Lines of N2O and CH4 Emission in Peatlands

Predicting N2O (nitrous oxide) and CH4 (methane) emissions from peatlands is challenging because of the complex coaction of biogeochemical factors. This study uses data from a global soil and gas sampling campaign. The objective is to analyse N2O and CH4 emissions in terms of peat physical and chemical conditions. Our study areas were evenly distributed across the A, C and D climates of the Koppen classification. Gas measurements using static chambers, groundwater analysis and gas and peat sampling for further laboratory analysis have been conducted in 13 regions evenly distributed across the globe. In each study area at least two study sites were established. Each site featured at least three sampling plots, three replicate chambers and corresponding soil pits and one observation well per plot. Gas emissions were measured during 2–3 days in at least three sessions. A log-log linear function limits N2O emissions in relation to soil TIN (total inorganic nitrogen). The boundary line of N2O in terms of soil temperature is semilog linear. The closest representation of the relationship between N2O and soil moisture is a local regression curve with its optimum at 60–70 %. Semilog linear upper boundaries describe the effects of soil moisture and soil temperature to CH4 best.

Effect of topography on soil erodibility in Kakuuto micro-catchment, Uganda

ABSTRACT Soil erodibility is a property that determines the vulnerability of a soil to erosion processes. Interrill erodibility of 7 soil types, haplic Luvisols, haplic Acrisols, skeletic Luvisols, skeletic Acrisols, rhodic skelectic Acrisols, ferric Acrisols, ferri Rhodic Acrisols of Kakuuto micro-catchment of the Lake Victoria basin was measured, and its toposequence pattern investigated using a portable rainfall simulator in the field. Simulated rainfall of 7 mm/min was applied for 5 min on 0.25 by 0.25 m plots; 16 tests were run on each soil type, under 2 moisture regimes (dry and wet). Results indicated that there were 2 groups of no pairewise significant difference in interill erodibility: haplic Acrisols, haplic Luvisols, Rhodic skeletic Acrisols, and skeletic Acrisols, ferric Acrisols, ferri rhodic Acrisols and skeletic Luvisols (p=0.011) being the second. The first group was more eroded than the second. Significant differences (p=0.05) were observed along the toposequence on interrill erodibility with an increase towards the footslope. The footslope interrill erodibility was 4.13 × 106kg/m2s while values of 1.05 × 106/kgm4s and 1.74 × 106/kg/m2s were observed at the upper and the middle landscape position; respectively.

Multi-stakeholder partnerships in value chain development: A case of the organic pineapple in Ntungamo district, Western Uganda

Purpose The purpose of this paper is to demonstrate that agricultural commodity value chain development using multi-stakeholder partnerships (MSPs) can fast-track improvement in the livelihoods of rural farming households. With the view that such partnerships can raise farmers’ incomes, the study uses the case of the organic pineapple (OP) value chain in Ntungamo, Western Uganda, to understand the governance features that hold the value chain partners together, to analyse the costs and margins to the participating farmers, to identify opportunities for demand-driven upgrading of the farmers’ skills and knowledge, and the role that partnerships play in such upgrading. Design/methodology/approach The study uses the qualitative tools of value chain analysis: value chain maps of stakeholders, processes and support services of the OP value chain, and a quantitative tool to analyse costs and margins to the participating farmers. Interviews were conducted with key informants from the OP innovation platform, and survey data collected for the planting season, February–July, 2014, across three farmer categories of certified organic, conventional, and farmers not participating in the innovation platform. Findings Careful selection of partnerships to develop the value chain is found to be critical. Partners to involve should be those that enable the upgrading of farmers’ knowledge, skills and technologies to position them for better markets. Partners should also include those that enable the improvement of margins to the farmers and efficiency of the value chain. The strategic MSPs should be bound by formal contracts, to ensure stable relationships in the value chain and hence sustainable market access for the farmers. Research limitations/implications Although carried out on a specific value chain in a specific local context, this is not likely to limit the applicability of the findings to commodity value chains in a range of local contexts. Originality/value The study fulfils the need to highlight the role that stakeholder partnerships can play in value chain development and how they can be sustained by governance and institutional arrangements.

Proxy quantification and mapping of seasonal rangeland herbage using grass cover in the cattle corridor of Uganda

This study aimed at estimating herbage mass functional relationship with rainfall and selected soil morphological properties using Geographic Information Systems (GIS). Herbage mass as dry matter (DM) measurements from quadrat harvesting method and estimations based on grass cover were done. Herbage on 1 × 1 m quadrats was harvested and oven dried at 60°C until constant weight. Grass cover data collection was based on spectral strata of vegetation cover types obtained from Landsat image. Rainfall data were collected from 14 rain gauge stations. Soil profiles were described and their drainage was determined. A multi-linear regression analysis was performed to determine the relationship among DM, grass cover, rainfall effectiveness and soil drainage. The relationships among the variables were integrated using ModelBuilder in ArcGIS 9.3 to come up with spatial and seasonal herbage distribution. Results showed a strong relationship among the above variables and DM (R 2 = 0.76; p < 0.001). Grass cover was found to be the important variable for herbage DM determination (R 2 = 0.73; p < 0.001). A correlation analysis of estimated and harvested DM resulted in a positive relationship (R 2 = 0.85). Estimated DM ranged between 895 and 1923 kg/ha with the highest DM during March–May and the lowest during September–November. This study demonstrated that grass is an important proxy measure of spatial and seasonal patterns of rangeland herbage mass. Therefore, rangeland herbage can in reality be monitored based on grass cover measurements to avoid or at least minimize the cost, destruction and information timeliness implications that are known to be associated with harvesting methods.

Nitrogen-rich organic soils under warm well-drained conditions are global nitrous oxide emission hotspots

Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3−), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3− and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3−-N kg−1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3− explains 69% of N2O emission, tropical wetlands should be a priority for N2O management.In a global field survey across a wide range of organic soils, the authors find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3–), water content and temperature. N2O emission increases with NO3– and temperature and follows a bell-shaped distribution with water content.