Spatially targeting the distribution of agricultural input stockists in Malawi

Developing the rural agricultural input markets in sub-Saharan Africa can improve the current low productivity of smallholder farmers. Malawi has seen significant efforts in addressing the availability of agricultural inputs at village level in the last few years; for example, the improvement of rural agro-dealer networks. Nevertheless inputs are still difficult to obtain for many remote smallholder farmers. Spatial analysis can help in the expansion of input stockists, especially agro-dealer networks, by assessing the coverage of existing input outlets and deriving optimum locations for village-level input stockists.We address three research questions. First, what is the locational efficiency of the current village-level stockists of inputs (Citizens Network for Foreign Affairs – Rural Agricultural Market Development Trust trained network of agro dealers and public sector)? Secondly, how many village-level stockists of markets are needed to reach 60% of the population in the central region of Malawi within one hour? Finally we address the potential spatial components of the sustainability of input stockists relating to the potential demand from smallholder farmers and the access to bulk supplies. The problem of finding the optimum location for village-level stockists of markets is addressed in two stages, using spatial analysis in conjunction with location–allocation models. First, the locational efficiency of the existing network of stockists of inputs is determined, followed by the establishment of a set of optimal sites for village-level stockists of inputs. A final step explores the viability of stockists and calculates the population surrounding the stockists taking into account competition from other sources of inputs and the accessibility of the selected stockists to potential wholesalers who are bulk distributors of farm inputs.Our results show that locational efficiency can be assessed in terms of the differential access of households to resources and transport. Often, these differences are not considered in covering problems and can have a large effect on the physical access to inputs. The results can be used to define which areas are inherently difficult to serve with agricultural inputs and could inform efforts to provide incentives to remote areas. Further implications for input policies in Malawi are that improvements in road infrastructure might not directly benefit the poorest farmers (if they are walking) but could serve to reduce the wholesale prices and therefore the retail price. In addition, the improvement in roads might increase the number of potential customers of any particular stockist, with economies of scale allowing the reduction of prices while ensuring a satisfactory profit margin for the stockist. The results of our models imply that Citizens Network for Foreign Affairs may need to train stockists over a wider area to increase the access to inputs of those smallholder farmers with least resources.     

Long-term changes in organic matter of woodland soils cleared for arable cropping in Zimbabwe

Subsistence farmers in Africa depend largely on the soil organic matter to sustain crop productivity. Long-term changes in soil organic carbon and nitrogen were measured after woodland clearance for smallholder subsistence farming or for commercial farming. The contents of organic carbon and nitrogen in soil under reference woodlands were largest (53.3 t C ha⁻¹, 4.88 t N ha⁻¹) in a red clay soil (∼ 50% clay + silt), followed by a granitic sand (∼ 12% clay + silt; 22.8 t C ha⁻¹, 1.47 t N ha⁻¹) and least (19.5 t C ha⁻¹, 0.88 t N ha⁻¹) in a Kalahari sand (∼ 5% clay + silt). Organic carbon declined rapidly under cultivation to attain new equilibria within 10 years on all smallholdings. Greatest losses occurred in soils that initially contained most carbon and nitrogen in the order: red clay (22.4 t C ha⁻¹ and 1.0 t N ha⁻¹) > granitic sand (13.2 t C ha⁻¹ and 0.8 t N ha⁻¹) > Kalahari sand (10.6 t C ha⁻¹ and 0.5 t N ha⁻¹). On the clay soil, commercial farming with intensive use of mineral fertilizers and incorporation of maize stover led to more gradual decline: at equilibrium, contents of carbon and nitrogen were 15 t C ha⁻¹ and 1.7 t N ha⁻¹ greater than on smallholdings with similar soil and climate. In the Kalahari sand the δ¹³C of organic C remained constant after woodland clearance, and maize contributed less than 10% of the total C even after 55 years. The δ¹³C signature increased slightly with increasing duration of cultivation by smallholders in the granitic sands and red clay soil where maize contributed 29% and 35% of the C at equilibrium. Under more productive commercial farming, the carbon derived from maize accounted for 50% of the total after 10 years of cultivation and 67% at equilibrium. The persistence of woodland carbon in the sandy soil is attributed to chemical stabilization resulting from large concentrations of lignin and polyphenols in the tree litter, or as charcoal.     

Nutrient use efficiencies and crop responses to N, P and manure applications in Zimbabwean soils: Exploring management strategies across soil fertility gradients

The spatial variability in crop yields commonly observed in smallholder farms of sub-Saharan Africa is often caused by gradients of declining soil fertility with increasing distance from the homestead. This heterogeneity means that recommendations based on regional soil surveys are of limited value. The variability in soil qualities within farms must be considered when designing management strategies, and their feasibility analysed by integrating results at the farm livelihood scale. For this purpose, we have developed the model FARMSIM, a dynamic bio-economic model for analysis and exploration of trade-offs in resource and labour allocation in heterogeneous smallholder farms. Focusing on farm-scale strategies, the approach to simulation of soil and crop processes in FARMSIM (the sub-model FIELD) is designed to be simple, but to keep the necessary degree of complexity to capture heterogeneity in resource use efficiencies. To test our approach, the sub-model FIELD was calibrated against chronosequences of woodland clearance in three agroecological zones of Zimbabwe (with soil textures of 3, 10, 35% clay), and used to simulate: (i) the creation of soil fertility gradients, and (ii) different strategies of N, P and manure applications to maize and soyabean rotations in homefields and outfields of smallholder farms on clayey and sandy soils. The results of the simulation of management strategies were tested against on-farm experimental data from Murewa, Zimbabwe. The model produced satisfactory predictions (r²: 0.6–0.9) of long-term changes in soil organic C, of crop responses to N and P and of nutrient use efficiencies across a wide range of yields and different field types. This demonstrated the broad applicability of the model despite the sparse data required for initialisation. However, the model results were less accurate in predicting crop responses to N and P applications in the outfields on sandy soils. Experimental evidence indicated yield limitation by Ca and Zn deficiencies in highly depleted outfields on sandy soils, which were not included mechanistically in the current version of FIELD. Repeated applications of 16 t ha⁻¹ year⁻¹ of manure allowed larger responses to applied N and P after 3 years of experimentation; such a corrective effect of manure was simulated to be due to improved N and P recovery efficiencies in the model. In combination with the experimental data, the simulation results suggested that soil fertility gradients affect nutrient use efficiencies, operating mostly on the efficiencies of nutrient capture rather than conversion. A typology of fields according to the type of management interventions needed is introduced, based on a generic application of FIELD with this parameterisation.     

Soil type,management history and current resource allocation: Three dimensions regulating variability in crop productivity on African smallholder farms

Soil fertility varies markedly within and between African smallholder farms, both as a consequence of inherent factors and differential management. Fields closest to homesteads (homefields) typically receive most nutrients and are more fertile than outlying fields (outfields), with implications for crop production and nutrient use efficiencies. Maize yields following application of 100 kg N ha⁻¹ and different rates and sources of P were assessed on homefields and outfields of smallholder farms in Zimbabwe. Soil organic carbon, available P and exchangeable bases were greater on the homefields than outfields. In each of three experimental seasons, maize yields in homefield control plots were greater than in the outfields of farms on a granitic sandy and a red-clay soil. Application of mineral N significantly increased maize yields on homefields in the first season (2.1–3.0 t ha⁻¹ on the clay soil and 1.0–1.5 t ha⁻¹ on the sandy soil) but the effects of N alone were not significant on the outfields due to other yield-limiting factors. Greatest yields of about 6 t ha⁻¹ were achieved on the clayey homefield with 100 kg N ha⁻¹ and 30 kg P ha⁻¹ applied as single super phosphate (SSP). Manure application gave greater yields (3–4 t ha⁻¹) than SSP (2–3 t ha⁻¹) in the sandy homefield and in the clayey outfield. Maize did not respond significantly to N, dolomitic lime, manure and P on the sandy outfield in the first and second seasons. In the third season, manure application (∼17 t manure ha⁻¹ year⁻¹) on the sandy outfield did result in a significant response in grain yields. Apparent P recovery in the first season was 55–65% when P was applied at 10 kg ha⁻¹ on the clayey homefield (SSP), clayey outfield (SSP and manure) and sandy homefield (manure) with apparent P recovery less than 40% when P was applied at 30 kg ha⁻¹. On the sandy outfield, P recovery was initially poor (<20%), but increased in the successive seasons with manure application. In a second experiment, less than 60 kg N ha⁻¹ was required to attain at least 90% of the maximum yields of 2–3 t ha⁻¹ on the sandy homefield and clayey outfield. N use efficiency varied from >50 kg grain kg⁻¹ N on the infields, to less than 5 kg grain kg⁻¹ N on the sandy outfields. Apparent N recovery efficiency by maize was greatest at small N application rates with P applied. We conclude that blanket fertilizer recommendations are of limited relevance for heterogeneous smallholder farms. Targeted application of mineral fertilizers and manure according to soil type and past management of fields is imperative for improving crop yields and nutrient use efficiencies.     

Nitrogen mineralization and maize yields following application of tree prunings to a sandy soil in Zimbabwe

Despite the promotion of prunings as sources of nitrogen for crops, lack of synchronization between N mineralization from prunings and plant uptake remains a major limitation to the impact of prunings on crop yields. A laboratory and a field experiment were therefore carried out to determine the mineralization patterns of selected prunings and assess the potential that exists to improve synchrony by mixing prunings of different quality. The laboratory incubation experiment was conducted for 84 days to determine the C and N release patterns of prunings of different quality and the manipulation of the C and N mineralization trends by mixing prunings of different quality. High quality prunings were considered to be those with high CO₂ evolution rates and mineralize N rapidly. The % C and % N released in 84 days were highest for the high quality prunings of Tithonia diversifolia (70% and 30% respectively) and least for the low quality prunings of Flemingia macrophylla (25% and –5% respectively). The medium quality prunings of Acacia angustissima and Calliandra calothyrsus had similar proportions of released C and N (about 40% C and 10% N). Different mixtures of T. diversifolia with other species showed contrasting influence on C release and N mineralization. Most mixtures released less C than that predicted, but in contrast most mixtures released N at a rate either matching or above the predicted. The % N released was strongly correlated with the polyphenol protein binding capacity (r² = 0.53) and also with the % C released (r² = 0.62). The field experiment was done for two cropping seasons to determine the effects of the prunings of these species and their mixtures on maize grain yield. The prunings were added at 5 t ha^–1 and incorporated into the top 15 cm by hand hoeing in the first season and their residual effects were monitored in the second season. Medium and low quality prunings produced significantly (p < 0.05) higher maize grain yields in the first season ranging between 2.4 t ha^–1 and 3.4 t ha^–1 compared with T. diversifolia which produced 1.7 t ha^–1. This suggested better synchrony in N release and uptake by maize with medium and low quality prunings compared with high quality prunings. The only mixture that indicated improved synchrony was the mixture of T. diversifolia and C. calothyrsus. This study showed that mixing prunings of different quality produce different patterns of N mineralization, some of which were unexpected and had a potential for improving N synchrony.This revised version was published online in November 2005 with corrections to the Cover Date.     

Communicating complexity: Integrated assessment of trade-offs concerning soil fertility management within African farming systems to support innovation and development

African farming systems are highly heterogeneous: between agroecological and socioeconomic environments, in the wide variability in farmers’ resource endowments and in farm management. This means that single solutions (or ‘silver bullets’) for improving farm productivity do not exist. Yet to date few approaches to understand constraints and explore options for change have tackled the bewildering complexity of African farming systems. In this paper we describe the Nutrient Use in Animal and Cropping systems - Efficiencies and Scales (NUANCES) framework. NUANCES offers a structured approach to unravel and understand the complexity of African farming to identify what we term ‘best-fit’ technologies - technologies targeted to specific types of farmers and to specific niches within their farms. The NUANCES framework is not ‘just another computer model’! We combine the tools of systems analysis and experimentation, detailed field observations and surveys, incorporate expert knowledge (local knowledge and results of research), generate databases, and apply simulation models to analyse performance of farms, and the impacts of introducing new technologies. We have analysed and described complexity of farming systems, their external drivers and some of the mechanisms that result in (in)efficient use of scarce resources. Studying sites across sub-Saharan Africa has provided insights in the trajectories of change in farming systems in response to population growth, economic conditions and climate variability (cycles of drier and wetter years) and climate change. In regions where human population is dense and land scarce, farm typologies have proven useful to target technologies between farmers of different production objectives and resource endowment (notably in terms of land, labour and capacity for investment). In such regions we could categorise types of fields on the basis of their responsiveness to soil improving technologies along soil fertility gradients, relying on local indicators to differentiate those that may be managed through ‘maintenance fertilization’ from fields that are highly-responsive to fertilizers and fields that require rehabilitation before yields can improved. Where human population pressure on the land is less intense, farm and field types are harder to discern, without clear patterns. Nutrient cycling through livestock is in principle not efficient for increasing food production due to increased nutrient losses, but is attractive for farmers due to the multiple functions of livestock. We identified trade-offs between income generation, soil conservation and community agreements through optimising concurrent objectives at farm and village levels. These examples show that future analyses must focus at farm and farming system level and not at the level of individual fields to achieve appropriate targeting of technologies - both between locations and between farms at any given location. The approach for integrated assessment described here can be used ex ante to explore the potential of best-fit technologies and the ways they can be best combined at farm level. The dynamic and integrated nature of the framework allows the impact of changes in external drivers such as climate change or development policy to be analysed. Fundamental questions for integrated analysis relate to the site-specific knowledge and the simplification of processes required to integrate and move from one level to the next.     

Effects of cattle manure on selected soil physical properties of smallholder farms on two soils of Murewa,Zimbabwe

The effects of cattle manure and inorganic N‐fertilizer application on soil organic carbon (SOC), bulk density, macro‐aggregate stability and aggregate protected carbon were determined on clay and sandy soils of the Murewa smallholder farming area, Zimbabwe. Maize was grown in four fields termed homefields (HFs) and outfields (OFs) because of spatial variability induced by management practices and with the following fertility treatments: control (no fertility amelioration), 5, 15 and 25 t/ha cattle manure + 100 kg/ha N applied annually for seven consecutive years. The addition of cattle manure resulted in significant (P < 0.01) increases in SOC, macro‐aggregate stability and aggregate protected carbon in clay soils from at least the 5 t/ha cattle manure rate and was comparable between HFs and OFs on clay soils. Aggregate protected carbon in clay soils was significantly higher from the 15 and 25 t/ha cattle manure rates compared to the 5 t/ha cattle manure treatment. In contrast, only SOC was significantly (P < 0.05) increased with the addition of cattle manure on the sandy soils, while bulk density, macro‐aggregate stability and aggregate protected carbon were not significantly changed. Bulk density was also not significantly (P > 0.05) different on the clay soils. A significant and positive linear relationship (r² = 0.85) was found between SOC and macro‐aggregate stability, while an r² value of 0.82 was obtained between SOC and aggregate protected carbon on the clay soils. However, no regressions were performed on data from the sandy soils because of the lack of significant changes in soil physical properties. Application of cattle manure and inorganic N‐fertilizer significantly increased (P < 0.05) maize grain yield on both soil types. Results show that inorganic N‐fertilizer combined with cattle manure at 5–15 t/ha per yr is necessary to increase maize yields and SOC on sandy soils in Murewa, while at least 15 t/ha per yr cattle manure is required on the clay soils to improve physical properties in addition to maize yields and SOC.     

Performance of bucket drip irrigation powered by treadle pump on tomato and maize/bean production in Malawi

The performance of a bucket drip irrigation system (BDI) powered by treadle pump was evaluated on tomato and intercropped maize/bean crops, between 2005 and 2007 in Malawi. It was a split plot experiment with three replicates. The BDI system consisted of a 1,300-l tank mounted 1.5 m above ground and connected with a 32-mm mainline and 15-mm lateral lines spaced at 1 m by 0.6 m. A treadle pump was used to uplift water to the tank. Tomato and intercropped maize/bean were irrigated every 4 days. The system reduced labour and water by >25% and it showed high uniform application depth and wetted diameter. Yields were significantly different between tomato varieties (P < 0.05). Maize/bean yields were highly significantly different between monoculture, intercropping system and bean varieties (P < 0.001). Consequently, an economic analysis shows that there is a significant difference, in terms of net income, between the various crop enterprises. Tomato was more valuable with BDI, compared to maize and beans. It can be concluded that BDI, powered by a treadle pump, saves labour and time and it provides uniform irrigation for crop production. Therefore, tomato is recommended for use with this system, compared to maize and bean.