Review of interventions and technologies for sustainable intensification of smallholder crop production in sub-humid sub-Saharan Africa

Besides low soil fertility, climate variability has often been identified as the major constraint to agricultural productivity in Sub-Saharan Africa (SSA), with rainfall variability (both within and across seasons) being the most critical. Traditionally, reasonable yields could be achieved in spite of constant or smaller resource inputs by expanding the cropped area, but this is no longer a viable option. Crop production intensification is required to produce more food per unit of input and land, while maintaining or rebuilding soil fertility. However, most smallholder farmers lack access to resources such cash, fertiliser and technological expertise to address constraints caused by the biophysical environments in which they operate. The objective of this review was to collate and appraise the range of crop production intensification options that have been developed for smallholder farmers in SSA. A case study from central Mozambique was included to illustrate the impact and relevance of locally feasible options to farmers who own different resources. The study has revealed that sustainable intensification of crop production requires that multiple constraints are addressed simultaneously, in this case primarily soil fertility/plant nutrient supply and weed management. Success of crop intensification options will also depend on proper targeting to different farm types as well as field soil fertility gradients. Although smallholder farmers in SSA have limited assets, the case study revealed the occurrence of local opportunities to increase current crop productivity which in some cases do not need substantial capital inputs by the farmers, but more efficient use and targeting

Food sovereignty in sub-Saharan Africa: reality, relevance, and practicality

Open Access Article; Published online: 07 Oct 2022The recent discourse on food sovereignty places much emphasis on democracy in determining localized food systems, and whether the food is culturally appropriate while leaning heavily on sustainable agricultural practices such as organic agriculture, ecological intensification, agroecology, naturebased solutions, and regenerative agriculture. Sustainable agricultural practices are intended to ensure that the land is managed without the use of synthetic fertilizers and pesticides, while going further by focusing on improvements on soil and land health. However, what are the practicalities of food activism and relying entirely on nature while yields are still very low in much of sub-Saharan Africa (SSA)? We attempt to answer this question in four main sections: (a) we start by defining the concept of food sovereignty and the associated practices, (b) we highlight some of the main socio-ecological conditions that are common in SSA, and (c) we present evidence of some of the limitations of food sovereignty due to the diversity in ecological, political, cultural, and socioeconomic contexts that characterize SSA; finally, (d) we focus on food preferences, marketing and certification aspects. We conclude that agroecology alone cannot solve the multiple objectives of increasing crop productivity and replenishing soil nutrients especially on small farms and relying on natural rainfall. There is an urgent need to combine superior crop varieties and judicious use of external inputs in tandem with the manipulation of the agroecological processes to increase the efficiency of input use and achieve higher food productivity, resilience to climate change, and preservation of the natural resource base in specific locations

Nuances and nuisances : Crop production intensification options for smallholder farming systems of southern Africa

Key words: crop production, intensification, extensification, farming systems, tradeoff analysis, maize, legume, manure, fertiliser, southern Africa Soil fertility decline and erratic rainfall are major constraints to crop productivity on smallholder farms in southern Africa. Crop production intensification along with efficient use of chemical fertiliser is required to produce more food per unit area of land, while rebuilding soil fertility. The objective of this thesis was to identify appropriate crop production intensification options that are suitable to the socio-economic and biophysical conditions of selected smallholder maize-based farming systems in southern Africa. Three sites that formed a gradient of intensity of crop and livestock production were selected for the study. Murehwa in Zimbabwe is characterised by the largest intensity followed by Ruaca and lastly Vunduzi both in central Mozambique. In all three sites, maize is a key staple and cash crop.A literature review, field methods based on participatory research, and modelling tools were combined in analysing potential crop production options across an agricultural intensification gradient. A meta-analysis on maize grain yieldunder rain-fed conditions revealed thatconservation agriculture required legume rotations and high nitrogen input use especially in the early years.Reduced tillage without mulch cover leads to lower yields than with conventional agriculture in low rainfall environments. Mulch cover in high rainfall areas leads to smaller yields than conventional tillage due to waterlogging, and improved yields under CA are likely on well drained soils. Crop productivity underconservation agriculture depends on the ability of farmers to achieve correct fertiliser application, timely weeding, and the availability of crop residues for mulching and systematic crop rotations which are currently lacking in southern Africa. Anadditive design of within-row intercropping was compared to a substitutive design with distinct alternating rows of maize and legume (local practice) under no-tillin the Ruaca and Vunduzi communities of central Mozambique. Intercropping increased productivity compared to the corresponding sole crops with land equivalent ratios (LER) of between 1.0 and 2.4. Maize yield loss was only 6-8% in within-row intercropping but 25-50% in the distinct-row option. Relay planting of maize and cowpea intercropping ensured cowpea yield when maize failed thus reduced the negative effects of dry spells. The residual benefits of maize-pigeonpea intercropping were large (5.6 t ha-1) whereas continuous maize (0.7 t ha-1) was severely infested by striga(Striga asiatica). The accumulation of biomass which provided mulch combined with no tillageincreased rainfall infiltration. Intensification through legume intercropping is a feasible option to increase crop productivity and farm income while reducing the risk of crop failureespecially where land limitation. Cattle manure in combination with chemical fertiliser that included N, P, Ca, Zn, Mn were evaluated for their potential to recover degraded soils and to support sustainable high crop productivity in Murehwa, Zimbabwe over nine years. The experiment was established on sandy and clay soils in two field types. Homefields were close to the homestead and relatively more fertile than the outfields due to previous preferential allocation of nutrients. Maize grain yields in sandy soils did not respond to the sole application of fertiliser N (remained less than 1 t ha-1); manure application had immediate and incremental benefits on crop yields in the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 on clay outfield, 7.6 t ha-1 on sandy homefield and 3.4 t ha-1 in the eighth season. Despite the large manure applications of up to 25 t ha-1, crop productivity and soil organic carbon build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. Manure can be used more efficiently if targeted to fields closest to homesteads but this exacerbates land degradation in the outfields and increases soil fertility gradients. The NUANCES-FARMSIM model for simulating crop and animal productivity in mixed crop-livestock farming systems was used to perform trade-off analysis with respect to crop residue management, animal and crop productivity in Murehwa, Zimbabwe. Retaining all maize residues in the field led to severe losses in animal productivity but significant gains in crop productivity in the long-term. Yield increased 4 to 5.6 t farm-1 for RG1, and from 2.8 to 3.5 t farm-1 for RG2. Body weight loss was on average 67 kg per animal per year for RG1 and 93 kg per animal per year for RG2. Retention of all crop residues reduced farm income by US37 and US38 per year for RG1 and RG2 respectively.Farmers who own cattle have no scope of retaining crop residues in the field as it results in significant loss of animal productivity. Non-livestock farmers (60% of the farmers) do not face trade-offs in crop residue allocation but have poor productivity compared to livestock owners and have a greater scope of retaining their crop residues if they invest in more labour to keep their residues during the dry season. This study has revealed that crop production intensification options developed without considering the biophysical conditions as well as socio-economic circumstances of farmers are nuisances. External ideas should be used to stimulate local innovations to push the envelope of crop production without creating new constraints on resource use. </p

Yield and labor relations of sustainable intensification options for smallholder farmers in sub-Saharan Africa. A meta-analysis

Sustainable intensification of agricultural production is needed to ensure increased productivity relative to inputs. Short-term yield returns and labor input are major determinants of the fate of sustainable intensification options on smallholder farms in sub-Saharan Africa because labor shortage is often acute, and most farmers lack access to labor-saving technologies. We assessed the relationship between maize grain yield change and labor input from a total of 28 published papers (631 data pairs) including subsets of data pairs within specific sustainable intensification practices. Among the reviewed technologies, manually dug planting basins showed ratios between the change in yield and change in labor inputs (Y/L) below 1, suggesting that labor demand increased more than yield. In contrast, ridging showed average Y/L values 2. No-till showed high Y/L (average1.7) when combined with herbicides but average Y/L 1 (total labor) when manually weeded. Manually weeded rotations showed average Y/L 1 and manually weeded intercropping systems average Y/L around 1. The relations revealed four scenarios: high yield returns but low labor demand, high yield returns and labor demand, low yield returns and labor demand, and low yield returns but high labor demand. High yield with high labor demand requires mostly investments in machinery and/or herbicides to reduce labor input. Low yield with low labor demand requires improved crop management, whereas low yield with high labor demand requires a combination of improved crop management and investments to reduce labor. This is the first comprehensive assessment showing that the sustainable intensification options being considered for smallholder farmers may increase crop yield but also labor demand. Options that include mechanization and herbicides at low cost are likely to be adopted due to their reduction effect on drudgery and total labor input

The potential of conservation agriculture to improve nitrogen fixation in cowpea under the semi-arid conditions of Kenya.

Open Access Journal; Published online: 07 Oct 2022Low-cost but productive crop intensification options are needed to assist smallholder farmers in the tropics to move away from poverty. This study assessed the capacity of cowpea (Vigna unguiculata (L.) Walp.) to perform biological N fixation (BNF) under no-tillage practices, crop residue cover and intercropping with maize (Zea mays L.). The study was performed during the long rains of 2017 at Kiboko experimental station, located in semi-arid eastern Kenya. The research field trials had been running for three years (6 cropping seasons) by the time the sampling took place. The experimental set up was a split-plot design: main plots being tillage system (no till + maize stover retention (CA), and conventional tillage to 15 cm depth without mulch retention (CT)), sub-plot being cropping system (maize-cowpea intercrop, maize monocrop, and cowpea monocrop). Cowpea plants were sampled at 50% flowering stage and at physiological maturity to investigate biomass production and %N derived from the atmosphere (%Ndfa) through the 15N natural abundance technique, using maize as a reference control. Results showed that the number of nodules per plant was higher in CA treatments rather than in CT although not significant (p>0.05). Mean cowpea grain yield at harvest varied between 472 – 590 kg ha‐1 in intercrops whereas grain yield in monocrops was between 1465 - 1618 kg ha-1. Significant differences were however recorded between treatments with CT monocropped cowpea at flowering recording the highest mean %Ndfa (62%) and CT intercrop the lowest (52%). At harvest stage CA inter recorded the highest %Ndfa (54%) while CT intercrop the lowest (41%). The %Ndfa was higher (p<0.05) at flowering (between 57- 69%) compared with 45 - 64 % at harvest stage. Overall cowpeas in intercrops derived between 17.8 - 22.8 kg ha-1 of their total N from atmospheric dinitrogen fixation while monocrops between 54.9 - 55.2 kg ha-1. The effect of CA on BNF was positive but not significantly different from CT. These results suggest that CA has the potential to enhance the BNF process but there is a need to explore in future alternative spatial arrangement and variety choice in intercropping of cowpea and maize to optimize the BNF process