Walter Mupangwa

Conservation agriculture in Southern Africa: Advances in knowledge

The increasing demand for food from limited available land, in light of declining soil fertility and future threats of climate variability and change have increased the need for more sustainable crop management systems. Conservation agriculture (CA) is based on the three principles of minimum soil disturbance, surface crop residue retention and crop rotations, and is one of the available options. In Southern Africa, CA has been intensively promoted for more than a decade to combat declining soil fertility and to stabilize crop yields. The objective of this review is to summarize recent advances in knowledge about the benefits of CA and highlight constraints to its widespread adoption within Southern Africa. Research results from Southern Africa showed that CA generally increased water infiltration, reduced soil erosion and run-off, thereby increasing available soil moisture and deeper drainage. Physical, chemical and biological soil parameters were also improved under CA in the medium to long term. CA increased crop productivity and also reduced on-farm labor, especially when direct seeding techniques and herbicides were used. As with other cropping systems, CA has constraints at both the field and farm level. Challenges to adoption in Southern Africa include the retention of sufficient crop residues, crop rotations, weed control, pest and diseases, farmer perception and economic limitations, including poorly developed markets. It was concluded that CA is not a ‘one-size-fits-all’ solution and often needs significant adaptation and flexibility when implementing it across farming systems. However, CA may potentially reduce future soil fertility decline, the effects of seasonal dry-spells and may have a large impact on food security and farmers’ livelihoods if the challenges can be overcome.

How climate-smart is conservation agriculture (CA)? – its potential to deliver on adaptation, mitigation and productivity on smallholder farms in southern Africa

Climate resilient cropping systems are required to adapt to the increasing threats of climate change projected for Southern Africa and to better manage current climate variability. Conservation agriculture (CA) has been proposed among technologies that are climate-smart. For a cropping system to be labelled “climate-smart” it has to deliver three benefits: a) adapt to the effects of climate and be of increased resilience; b) mitigate climate effects by sequestering carbon (C) and reducing greenhouse gas emissions (GHG); and c) sustainably increase productivity and income. Research on smallholder farms from Southern Africa was analysed to assess if CA can deliver on the three principles of climate-smart agriculture. Results from Southern Africa showed that CA systems have a positive effect on adaptation and productivity, but its mitigation potential lags far behind expectations. CA systems maintain higher infiltration rates and conserve soil moisture, which helps to overcome seasonal dry-spells. Increased productivity and profitability were recorded although a lag period of 2–5 cropping seasons is common until yield benefits become significant. Immediate economic benefits such as reduced labour requirements in some systems will make CA more attractive in the short term to farmers who cannot afford to wait for several seasons until yield benefits accrue. The available data summarizing the effects of CA on soil organic C (SOC) and reductions in greenhouse gases, are often contradictory and depend a great deal on the agro-ecological environment and the available biomass for surface residue retention. There is an urgent need for more research to better quantify the mitigation effects, as the current data are scanty. Possible co-interventions such as improved intercropping/relay cropping systems, agroforestry and other tree-based systems may improve delivery of mitigation benefits and need further exploration.

Complementary practices supporting conservation agriculture in southern Africa. A review

Conservation agriculture (CA)—the simultaneous application of minimum soil disturbance, crop residue retention, and crop diversification—is a key approach to address declining soil fertility and the adverse effects of climate change in southern Africa. Applying the three defining principles of CA alone, however, is often not enough, and complementary practices and enablers are required to make CA systems more functional for smallholder farmers in the short and longer term. Here, we review 11 complementary practices and enablers grouped under six topical areas to highlight their critical need for functional CA systems, namely: (1) appropriate nutrient management to increase productivity and biomass; (2) improved stress-tolerant varieties to overcome biotic and abiotic stresses; (3) judicious use of crop chemicals to surmount pest, diseases, and weed pressure; (4) enhanced groundcover with alternative organic resources or diversification with green manures and agroforestry; (5) increased efficiency of planting and mechanization to reduce labor, facilitate timely planting, and to provide farm power for seeding; and (6) an enabling political environment and more harmonized and innovative extension approaches to streamline and foster CA promotional efforts. We found that (1) all 11 complementary practices and enablers substantially enhance the functioning of CA systems and some (e.g., appropriate nutrient management) are critically needed to close yield gaps; (2) practices and enablers must be tailored to the local farmer contexts; and (3) CA systems should either be implemented in a sequential approach, or initially at a small scale and grow from there, in order to increase feasibility for smallholder farmers. This review provides a comprehensive overview of practices and enablers that are required to improve the productivity, profitability, and feasibility of CA systems. Addressing these in southern Africa is expected to stimulate the adoption of CA by smallholders, with positive outcomes for soil health and resilience to climate change.

Precision Agriculture and Food Security in Africa

Background and Significance of the topic: The chapter gives an overview of precision agriculture and its impacts on food security in Africa. Methodology: Methods and concepts of precision agriculture are described including crop, soil and position sensors; which include global positioning and remote sensing applications in detection of crop stress, monitoring variability, soils, weeds, and diseases. Machine controls and computer based systems are also briefly described. Application/Relevance to systems analysis: There are a number of operations that can benefit from precision agriculture at field level, including soil preparation, fertilisation, irrigation and weed management. In Africa, the benefits of precision agriculture include improved food security through increases in water and nutrient use efficiency, and timely management of activities such as weed control. Precision agriculture has saved costs of inputs in both commercial and smallholder farming in Africa. Pollution control of ground and surface water sources has slowed down where fertiliser and agrochemical applications are now more efficient. Policy and/or practice implications: Two examples of precision agriculture application in Africa are presented; FruitLook which is used by farmers in the Western Cape in South Africa as a state-of the art information technology that helps deciduous fruit and grape farmers to be water efficient and climate-smart. The Chameleon and Wetting Front Detector Sensors have enabled small scale farmers in Mozambique, Tanzania, and Zimbabwe to cut down irrigation frequency fifty times and double productivity. Discussion and conclusion: It is clear that precision agriculture has played a major role in improving food security in Africa through the efficient use of inputs such as fertiliser and water, while also reducing environmental pollution and degradation.

FERTILIZATION STRATEGIES IN CONSERVATION AGRICULTURE SYSTEMS WITH MAIZE–LEGUME COVER CROP ROTATIONS IN SOUTHERN AFRICA

Multilocation experiments were established to determine the best strategy for using inorganic fertilizer in conservation agriculture (CA) systems that use green manure cover crops, namely sunhemp, velvet bean and cowpea grown in rotation with maize. The objectives of the study were to determine (i) the effect of half and full rates of basal fertilizer on maize and legume biomass yields, (ii) the residual effects of unfertilized, half and fully fertilized green manure legumes on maize grown after the legumes, and (iii) the residual effect of unfertilized, half and fully fertilized green manure legumes combined with basal and topdressing fertilizer on maize yields. Experimental design was a randomized complete block with basal fertilizer as a treatment in the green manure legumes phase. Previously, in the maize phase, green manure legume species were the main treatment with basal fertilizer as a subtreatment (sunhemp, velvet bean and cowpea: 0, 75, 150 kg ha −1 and 0, 50, 100 kg ha −1 , respectively). Nitrogen was applied in the maize phase at 0, 23, 46, 69 kg N ha −1 as a sub-subtreatment in Malawi. Results showed that inorganic fertilizer is the most effective when applied to the maize, not green manure legumes. Biomass of green manure legumes, sunnhemp 8084 kg ha −1 , velvet bean 7678 kg ha −1 and cowpea 4520 kg ha −1 , was not significantly affected by application of basal fertilizer. Maize production increased after the application of green manure legumes with maize-after-maize, maize-after-velvet bean, maize-after-sunnhemp and maize-after-cowpea, yielding 3804, 5440, 5446 and 5339 kg ha −1 , respectively. Nitrogen increased maize yield regardless of the previously used green manure legumes species. Our results suggest that farmers should apply fertilizer to maize and grow green manure legumes on residual soil in CA systems. Despite growing green manure legumes, smallholders should apply nitrogen topdressing to maize grown using the green manure legumes in some agro-ecologies.

Maize Yields in Varying Rainfall Regimes and Cropping Systems Across Southern Africa: A Modelling Assessment

Rainfall variability, which ultimately leads to climate change, is a major threat to smallholder agriculture. It affects time of sowing time and productivity, amongst other challenges. There is therefore need to evaluate the different strategies for their effectiveness in managing climate variability. This study assessed the effects of different strategies on sowing date, season length and maize yields under variable rainfall conditions. Maize (Zea mays L.) yield simulations for Southern Africa were conducted using the DSSAT model. Simulated conservation agriculture (CA)-based cropping systems included basins prepared early (CA-Basins early) and late (CA-Basins late), draught powered planter (CA-Direct seeder), ripper (CA-Ripper) and Dibble stick (CA-Dibble). Conventional systems were mouldboard ploughing early (CMP-early) and late (CMP-late). Rainfall seasons were classified into low, medium and high based on the total rainfall amount. Results showed that high-rainfall seasons were seeded earlier and had a greater season length compared to low rainfall seasons in drier agro-ecologies, translating to higher yields and vice versa. Reduced labour requirements and use of draught power, enabled early seeding of CA-ripper, direct seeder, basins early and CMP-early systems compared to CA-Basins late, Dibble stick and CMP-late systems. However, performance of cropping systems did not vary across season types suggesting that there was thus no evidence of higher yield advantages from CA technologies even during low rainfall seasons. This puts the merits of drought mitigation by CA technologies into doubt despite enabling early planting.

Maize responses to reduced tillage, different plant residue mulch and nitrogen fertiliser on granitic sandy soils of Zimbabwe

Mulching in smallholder conservation agriculture (CA) systems is constrained by lack of adequate crop residues. A three-year study assessed the effects of reduced tillage systems combined with different plant residue mulch and nitrogen (N) fertiliser on nitrogen uptake using the normalised difference vegetation index (NDVI), maize growth and yield, and agronomic efficiency. A split plot design with three or four replicates was used. Maize, Hyparrhenia grass, leaf litter, sunnhemp and Tephrosia residue mulch in CA and a conventional control were the main treatments. The N subtreatments were 0, 60 and 120 kg N ha−1. The main treatments had a similar effect on NDVI, and N increased NDVI across the treatments. The conventional practice had taller plants compared with CA. The conventional and CA treatments had a similar effect on maize yields. The different plant residues in CA had a similar effect on yields. Nitrogen increased yield, and 60 and 120 kg N ha−1 had a similar effect. The 60 kg N ha−1 subtreatment had a higher agronomic N efficiency than 120 kg N ha−1. The study demonstrated that CA with different plant residues and the conventional practice give similar yields in the short term.

Productivity and profitability of manual and mechanized conservation agriculture (CA) systems in Eastern Zambia

Climate variability and declining soil fertility pose a major threat to sustainable agronomic and economic growth in Zambia. The objective of this study was to assess crop yield, land and labor productivity of conservation agriculture (CA) technologies in Eastern Zambia. On-farm trials were run from 2012–2015 and farmers were replicates of a randomized complete block design. The trials compared three CA systems against a conventional practice. Yield and net return ha −1 were determined for maize and legume yield (kg ha −1 ) produced by ridge and furrow tillage, CA dibble stick planting, CA animal traction ripping and direct seeding. The dibble stick, ripline and direct seeding CA systems had 6–18, 12–28 and 8–9% greater maize yield relative to the conventional tillage system, respectively. Rotation of maize with cowpea and soybean significantly increased maize yields in all CA systems. Intercropping maize with cowpea increased land productivity (e.g., the land equivalent ratio for four seasons was 2.01) compared with full rotations under CA. Maize/cowpea intercropping in dibble stick CA produced the greatest net returns (US

Evaluating manual conservation agriculture systems in southern Africa

312-767 ha −1 ) compared with dibble stick maize-cowpea rotation (US

Where is the limit? lessons learned from long-term conservation agriculture research in Zimuto Communal Area, Zimbabwe

204-657), dibble stick maize monoculture (US