A road to food? : efficacy of nutrient management options targeted to heterogeneous soilscapes in the Teso farming system, Uganda

Key words: Land use change; Heterogeneity in soil fertility; Targeting; Integrated soil fertility management; Nutrient use efficiencies; Rehabilitation of degraded fields; Fertiliser requirements, Finger millet; QUEFTS model; Smallholder systems; sub-Saharan Africa. Poor soil fertility in smallholder farming systems in sub-Saharan Africa is recognised as a major factor responsible for low per capita food production and escalating food insecurity. Increasing food production in most smallholder farming systems requires intensification with nutrient inputs. Targeting nutrient management interventions to heterogeneity can greatly enhance the use efficiency of the scarce nutrient inputs and can help in identification of ‘best fits’ (most suitable options for niches within the systems). This thesis aimed at contributing to understanding how to target nutrient management options to heterogeneity for improved crop production in the Teso farming system in eastern Uganda. Land use change analysis between 1960 and 2001 showed that 48-78% more land was brought into cultivation and disappearance of communal grazing lands. Productivity of the farming system is also low. Population growth, political-instability-mediated collapse of institutions that supported production and marketing of cotton, and cattle rustling account for the changes in land use and productivity of the system. Balances of N, P and K were positive on larger farms (LF) and negative on the medium farms (MF), small farms with cattle (SF1) and without cattle (SF2), but were negative at the crop scale on all the farm types. Livestock, crop yield, labour availability and access to off farm income are the sustainability indicators in the system. There were no topographic-gradients in soil pH, SOC, total N, Exch. Mg, Exch. Ca, Exch. K, CEC, sand and clay in the two villages with different geo-morphological features characterised except for extractable P which was 3 - 5 times higher in the in the top soils of the profiles in the valley bottoms than those in the upper landscape position of the toposequences. Soil organic carbon (SOC) concentrations significantly differed (P Heterogeneity in soil fertility affected performance of legumes established with and without P and their residual effect on subsequent finger millet crops. Legume biomass and N accumulation differed significantly (P Application of N, P fertilisers alone (0, 30, 60, 90 kg ha–1), N+P at equal rates of single application, and manure (3 t ha–1) supplemented with N (0, 30, 60 and 90 kg ha–1) to degraded fields closed the within farm yield gap in finger millet by only 24%-43 %. The inability of the options to close the yield differences was because of poor nutrient use efficiencies ( Using the Quantitative Evaluation of Fertility of Tropical Soils (QUEFTS) model calibrated for finger millet, balanced fertiliser requirements for a target millet yield of 2000 kg ha–1 was estimated at 83 kg N ha–1 and 52 kg P ha–1 and 56 kg K ha–1 for the sandy loam soils of Chelekura village and 64 kg N ha–1 and 31 kg P ha–1 and 40 kg K ha–1 for the sandy clay loam soils in Onamudian village. Targeting nutrient management options can result in larger benefits from nutrient management interventions and specific attention can be afforded to specific constraints to avoid wastage of resources. Combining organic resources and mineral fertilisers is needed for higher crop yields and nutrient use efficiencies. However, the SOC thresholds for higher mineral fertiliser use efficiencies need to be determined for different soil types (silt + clay) and crops as well as making farm/ system scale reconfigurations of cropping systems that will enhance efficiency in resource use. Supportive policy frameworks should be put in place to enhance investment in soil fertility management and thus increase food production. <br/

Drivers of land use change and household determinants of sustainability in smallholder farming systems of Eastern Uganda

Smallholder farming systems in sub-Saharan Africa have undergone changes in land use, productivity and sustainability. Understanding of the drivers that have led to changes in land use in these systems and factors that influence the systems’ sustainability is useful to guide appropriate targeting of intervention strategies for improvement. We studied low input Teso farming systems in eastern Uganda from 1960 to 2001 in a place-based analysis combined with a comparative analysis of similar low input systems in southern Mali. This study showed that policy-institutional factors next to population growth have driven land use changes in the Teso systems, and that nutrient balances of farm households are useful indicators to identify their sustainability. During the period of analysis, the fraction of land under cultivation increased from 46 to 78%, and communal grazing lands nearly completely disappeared. Cropping diversified over time; cassava overtook cotton and millet in importance, and rice emerged as an alternative cash crop. Impacts of political instability, such as the collapse of cotton marketing and land management institutions, of communal labour arrangements and aggravation of cattle rustling were linked to the changes. Crop productivity in the farming systems is poor and nutrient balances differed between farm types. Balances of N, P and K were all positive for larger farms (LF) that had more cattle and derived a larger proportion of their income from off-farm activities, whereas on the medium farms (MF), small farms with cattle (SF1) and without cattle (SF2) balances were mostly negative. Sustainability of the farming system is driven by livestock, crop production, labour and access to off-farm income. Building private public partnerships around market-oriented crops can be an entry point for encouraging investment in use of external nutrient inputs to boost productivity in such African farming systems. However, intervention strategies should recognise the diversity and heterogeneity between farms to ensure efficient use of these external inputs

Impacts of heterogeneity in soil fertility on legume-finger millet productivity, farmers ' targeting and economic benefits

Targeting of integrated management practices for smallholder agriculture in sub-Saharan Africa is necessary due to the great heterogeneity in soil fertility. Experiments were conducted to evaluate the impacts of landscape position and field type on the biomass yield, N accumulation and N2-fixation by six legumes (cowpea, green gram, groundnut, mucuna, pigeonpea and soyabean) established with and without P during the short rain season of 2005. Residual effects of the legumes on the productivity of finger millet were assessed for two subsequent seasons in 2006 in two villages in Pallisa district, eastern Uganda. Legume biomass and N accumulation differed significantly (P <0.001) between villages, landscape position, field type and P application rate. Mucuna accumulated the most biomass (4.8–10.9 Mg ha-1) and groundnut the least (1.0–3.4 Mg ha-1) on both good and poor fields in the upper and middle landscape positions. N accumulation and amounts of N2-fixed by the legumes followed a similar trend as biomass, and was increased significantly by application of P. Grain yields of finger millet were significantly (P <0.001) higher in the first season after incorporation of legume biomass than in the second season after incorporation. Finger millet also produced significantly more grain in good fields (0.62–2.15 Mg ha-1) compared with poor fields (0.29–1.49 Mg ha-1) across the two villages. Participatory evaluation of options showed that farmers preferred growing groundnut and were not interested in growing pigeonpea and mucuna. They preferentially targeted grain legumes to good fields except for mucuna and pigeonpea which they said they would grow only in poor fields. Benefit-cost ratios indicated that legume-millet rotations without P application were only profitable on good fields in both villages. We suggest that green gram, cowpea and soyabean without P can be targeted to good fields on both upper and middle landscape positions in both villages. All legumes grown with P fertiliser on poor fields provided larger benefits than continuous cropping of millet

Dilemma of nitrogen management for future food security in sub-Saharan Africa – a review

Article purchased; Published online: 13 July 2017Food security entails having sufficient, safe, and nutritious food to meet dietary needs. The need to optimise nitrogen (N) use for nutrition security while minimising environmental risks in sub-Saharan Africa (SSA) is overdue. Challenges related to managing N use in SSA can be associated with both insufficient use and excessive loss, and thus the continent must address the ‘too little’ and ‘too much’ paradox. Too little N is used in food production (80% of countries have N deficiencies), which has led to chronic food insecurity and malnutrition. Conversely, too much N load in water bodies due mainly to soil erosion, leaching, limited N recovery from wastewater, and atmospheric deposition contributes to eutrophication (152 Gg N year–1 in Lake Victoria, East Africa). Limited research has been conducted to improve N use for food production and adoption remains low, mainly because farming is generally practiced by resource-poor smallholder farmers. In addition, little has been done to effectively address the ‘too much’ issues, as a consequence of limited research capacity. This research gap must be addressed, and supportive policies operationalised, to maximise N benefits, while also minimising pollution. Innovation platforms involving key stakeholders are required to address N use efficiency along the food supply chain in SSA, as well as other world regions with similar challenges

Dynamics of forest cover conversion in and around Bwindi impenetrable forest, Southwestern Uganda

Forest cover has been converted to agricultural land use in and around the protected areas of Uganda. The objectives of this study were; to examine the dynamics of forest cover change in and around Bwindi impenetrable forest between 1973 and 2010 and to identify the drivers of forest cover change. The trend in forest cover change was assessed by analyzing a series of orthorectified landsat imageries of 1973, 1987 and 2001 using unsupervised and supervised classification. Land use/cover map for 2010 was reconstructed by analyzing 2001 image, validated and/or reconstructed by ground truthing, use of secondary data and key informant interviews. A series of focused group discussions and key informant interviews were also used to identify drivers of land use/cover change. Policies and institutional arrangements that could have affected forest cover change for the studied time period were also identified. Results showed that protected forest and woodlot in unprotected area had declined by 7.8% and 70.7% respectively as small scale farming and tea plantations had increased by 13.9% and 78.3% respectively between 1973 and 2010. The conversions were attributed to land use pressure due to population growth, change in socio-economic conditions and institutional arrangements. The severe loss of woodlot outside the protected area not only poses a potential threat to the protected forest but also calls for intervention measures if efforts to mitigate climate change impacts are to be realized

Efficacy of nutrient management options for finger millet production on degraded smallholder farms in eastern Uganda

Open Access Journal; Published online: 30 Sep 2021Poor soil fertility is a major problem constraining crop productivity in smallholder farms of sub-Saharan Africa due to inadequate nutrient replenishment. Differential management of nutrients creates areas of accumulation and depletion of nutrients within farms with the latter increasing in spatial coverage. Nutrient additions are required to increase crop production in such degraded areas. We used experimental data to evaluate the potential of inorganic fertilizers and organic manures to offset finger millet yield differences or gap between degraded fields and former kraals, which are recognized as niches for obtaining the best yields within the Teso farming system in eastern Uganda. Nitrogen (N) and phosphorus (P) fertilizers were sole applied at 0, 30, 60, and 90 kg ha−1 and in combination (N+P) at equal rates of sole application, and manure (3 t ha−1) supplemented with N (0, 30, 60, and 90 kg ha−1) to degraded fields located in upper and middle landscape positions in Chelekura and Onamudian villages. A second control treatment of finger millet grown on soils of former kraal sites (high fertility niches) was included as a benchmark to evaluate the efficacy of nutrient management options on degraded field. Average grain yield ranged from 404 to 2,026 kg ha−1 and differed significantly (p < 0.001) between villages and seasons. Significant effects (p < 0.05) of landscape position on grain yield were observed only in Onamudian village. Although the treatments significantly increased millet yields on degraded fields above the control, they could not eliminate the yield differences between degraded fields and former kraals. The largest average grain yields on degraded fields were obtained from combined application of N+P resulting in average grain yields of 800 and 1,171 kg ha−1 in Chelekura village and Onamudian village, respectively. These yield responses resulted in only 24 and 43% of yields obtained on former kraal fields in Chelekura and Onamudian, respectively. The physiological efficiencies, agronomic efficiencies, and apparent recoveries of N and P were low; often <25%. Pot experiments conducted in a greenhouse showed that Sulphur (S) and potassium (K) were additional limiting nutrients to N and P for finger millet production in Chelekura and Onamudian and may partly explain the large yield differences of finger millet between fertilized fields and former kraals in the smallholder farming systems. Nutrient management strategies for sustainable millet production in these farming systems need consideration of site-specific nutrient limitations

Soyabean response to rhizobium inoculation across sub-Saharan Africa: Patterns of variation and the role of promiscuity

Article purchased; Published online: 7 Sept 2017Improving bacterial nitrogen fixation in grain legumes is central to sustainable intensification of agriculture in sub-Saharan Africa. In the case of soyabean, two main approaches have been pursued: first, promiscuous varieties were developed to form effective symbiosis with locally abundant nitrogen fixing bacteria. Second, inoculation with elite bacterial strains is being promoted. Analyses of the success of these approaches in tropical smallholder systems are scarce. It is unclear how current promiscuous and non-promiscuous soyabean varieties perform in inoculated and uninoculated fields, and the extent of variation in inoculation response across regions and environmental conditions remains to be determined. We present an analysis of on-farm yields and inoculation responses across ten countries in Sub Saharan Africa, including both promiscuous and non-promiscuous varieties. By combining data from a core set of replicated on-farm trials with that from a large number of farmer-managed try-outs, we study the potential for inoculation to increase yields in both variety types and evaluate the magnitude and variability of response. Average yields were estimated to be 1343 and 1227 kg/ha with and without inoculation respectively. Inoculation response varied widely between trials and locations, with no clear spatial patterns at larger scales and without evidence that this variation could be explained by yield constraints or environmental conditions. On average, specific varieties had similar uninoculated yields, while responding more strongly to inoculation. Side-by side comparisons revealed that stronger responses were observed at sites where promiscuous varieties had superior uninoculated yields, suggesting the availability of compatible, effective bacteria as a yield limiting factor and as a determinant of the magnitude of inoculation response

Dynamics of forest cover conversion in and around Bwindi impenetrable forest, Southwestern Uganda

Forest cover has been converted to agricultural land use in and around the protected areas of Uganda. The objectives of this study were; to examine the dynamics of forest cover change in and around Bwindi impenetrable forest between 1973 and 2010 and to identify the drivers of forest cover change. The trend in forest cover change was assessed by analyzing a series of orthorectified landsat imageries of 1973, 1987 and 2001 using unsupervised and supervised classification. Land use/cover map for 2010 was reconstructed by analyzing 2001 image, validated and/or reconstructed by ground truthing, use of secondary data and key informant interviews. A series of focused group discussions and key informant interviews were also used to identify drivers of land use/cover change. Policies and institutional arrangements that could have affected forest cover change for the studied time period were also identified. Results showed that protected forest and woodlot in unprotected area had declined by 7.8% and 70.7% respectively as small scale farming and tea plantations had increased by 13.9% and 78.3% respectively between 1973 and 2010. The conversions were attributed to land use pressure due to population growth, change in socio-economic conditions and institutional arrangements. The severe loss of woodlot outside the protected area not only poses a potential threat to the protected forest but also calls for intervention measures if efforts to mitigate climate change impacts are to be realized

Consistency, variability, and predictability of on-farm nutrient responses in four grain legumes across east and west Africa

Open Access Article; Published online: 26 May 2023Grain legumes are key components of sustainable production systems in sub-Saharan Africa, but wide-spread nutrient deficiencies severely restrict yields. Whereas legumes can meet a large part of their nitrogen (N) requirement through symbiosis with N2-fixing bacteria, elements such as phosphorus (P), potassium (K) and secondary and micronutrients may still be limiting and require supplementation. Responses to P are generally strong but variable, while evidence for other nutrients tends to show weak or highly localised effects. Here we present the results of a joint statistical analysis of a series of on-farm nutrient addition trials, implemented across four legumes in four countries over two years. Linear mixed models were used to quantify both mean nutrient responses and their variability, followed by a random forest analysis to determine the extent to which such variability can be explained or predicted by geographic, environmental or farm survey data. Legume response to P was indeed variable, but consistently positive and we predicted application to be profitable for 67% of farms in any given year, based on prevailing input costs and grain prices. Other nutrients did not show significant mean effects, but considerable response variation was found. This response heterogeneity was mostly associated with local or temporary factors and could not be explained or predicted by spatial, biophysical or management factors. An exception was K response, which displayed appreciable spatial variation that could be partly accounted for by spatial and environmental covariables. While of apparent relevance for targeted recommendations, the minor amplitude of expected response, the large proportion of unexplained variation and the unreliability of the predicted spatial patterns suggests that such data-driven targeting is unlikely to be effective with current data