Isaiah Nyagumbo

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.

Adoption Potential of Conservation Agriculture Practices in Sub-Saharan Africa: Results from Five Case Studies

Despite the reported benefits of conservation agriculture (CA), its wider up-scaling in Sub-Saharan Africa (SSA) has remained fairly limited. This paper shows how a newly developed qualitative expert assessment approach for CA adoption (QAToCA) was applied to determine its adoption potential in SSA. CA adoption potential is not a predictor of observed adoption rates. Instead, our aim was to systematically check relevant factors that may be influencing its adoption. QAToCA delivers an assessment of how suitable conditions “and thus the likelihood for CA adoption” are. Results show that the high CA adoption potentials exhibited by the Malawi and Zambia case relate mostly to positive institutional factors. On the other hand, the low adoption potential of the Zimbabwe case, in spite of observed higher estimates, is attributed mainly to unstable and less secured market conditions for CA. In the case of Southern Burkina Faso, the potential for CA adoption is determined to be high, and this assessment deviates from lower observed figures. This is attributed mainly to strong competition of CA and livestock for residues in this region. Lastly, the high adoption potential found in Northern Burkina Faso is explained mainly by the fact that farmers here have no alternative other than to adopt the locally adapted CA system—Zaï farming. Results of this assessment should help promoters of CA in the given regions to reflect on their activities and to eventually adjust or redesign them based on a more explicit understanding of where problems and opportunities are found.

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.

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.