Ernest Dube

Winter cover crops and fertiliser effects on the weed seed bank in a low-input maize-based conservation agriculture system

This study investigated the effects of grazing vetch (Vicia dasycarpa L.) and oat (Avena sativa L.) cover crops and fertiliser on the seed bank of some problematic weeds in a maize-based conservation agriculture system. Soil sampling for seed bank analysis was carried out at the 0–5 and 5–20 cm depths after four years of rotations. The winter cover crops reduced the seed-bank density of Digitaria sanguinalis (L.) Scop., Eleusine indica (L.) Gaertn., Amaranthus retroflexus L. and Datura stramonium L. in the 0–5 cm depth by 30–70%. Vetch was more effective on depleting the D. sanguinalis seed bank than oat. Fertiliser application reduced the A. retroflexus seed bank by 41.6% in the weedy fallow, but had no significant effect in plots grown to the cover crops. The winter cover crops did not significantly affect seed-bank weed species diversity.

Identifying high-yielding dryland wheat cultivars for the summer rainfall area of South Africa

Drought is a major challenge to dryland wheat (Triticum aestivum L.) production in the summer rainfall area (SRA) of South Africa. Dryland wheat farming in the SRA is unique in that the crop is dry-planted on high-water-table soils in winter, relying on stored moisture for germination and vegetative growth. Drought risk is high as only 260–300 mm rainfall is received during the growth period of the wheat from May to December. A number of new, improved dryland wheat cultivars released for the SRA during the recent period from 2003 to 2012 were evaluated for yield over several seasons under the National Wheat Cultivar Evaluation Program. As preliminary work for improving drought tolerance of wheat in the SRA, yield data of this genetic pool was re-analysed to identify the best-adapted cultivars based on means and coefficients of variation across years and geographic regions. Cultivars SST 347, PAN 3120, SST 356, PAN 3377, Matlabas, PAN 3161, PAN 3368, PAN 3379, PAN 3144, PAN 3355 and PAN 3118 had above-average yield and stability. These are recommended for adoption by farmers, as well as possible utilisation by researchers in improving drought tolerance of wheat.

Conservation agriculture effects on plant nutrients and maize grain yield after four years of maize–winter cover crop rotations

The effects of maize rotation with oat (Avena sativa cv. Sederberg) and grazing vetch (Vicia dasycarpa cv. Max) winter cover crops on nutrient availability, maize grain yield and maize grain nutrient concentration were investigated. Soil samples were collected from the 0–5 and 5–20 cm depths of experimental plots after four years of continuous maize–winter cover crop rotations. Winter cover crops caused small increases of extractable soil Cu, Mn, P and Zn, but not Ca and K, concentrations. A small dose of fertiliser applied to maize (60, 30, 40 and 1.5 kg ha−1 of N, P, K and Zn, respectively) also caused a significant increase in P and Zn, as well as mineral N, concentrations but only in the vetch–maize rotations. Stratification of Mn, K and Zn in the 0–5 cm soil depth occurred in all treatments. Vetch additionally increased maize grain yield, grain N concentration and soil acidity more than either oat or fallow. Non-fertilisation of maize reduced maize grain yield on oat and fallow–maize rotations more than it did on vetch–maize rotations. A combined application of vetch winter cover crops and small doses of fertiliser could significantly improve sustainability of low input maize-based conservation agriculture systems.

A vetch winter cover crop can improve response to nitrogen fertiliser and profitability of no-till maize : short communication

A high nitrogen (N) fertiliser requirement can be a deterrent to the adoption of conservation agriculture (CA). A field trial was carried out to test whether a high biomass-yielding vetch (Vicia dasycarpa L.) winter cover crop can be used to improve N response and profitability of a subsequent maize (Zea mays L.) crop under no-till and irrigation. There were five N fertilisation treatments (0, 60, 120, 180 and 240 kg ha−1). Maize grain yield after vetch was higher than that after a fallow (no winter cover crop) for most of the cases when the N fertiliser application rate was below 180 kg ha−1. Where no N fertiliser was applied, maize yields after vetch were 4.71 and 7.26 tons ha−1 for the first and second seasons, translating into an N fertiliser replacement value of approximately 90 kg N ha−1. The highest marginal rate of return for vetch over the two maize seasons (399% and 649%) was obtained at a fertiliser rate of 0 kg N ha−1. These data from preliminary CA studies in the Eastern Cape highlight the importance of promoting legume winter cover crops as an entry point to CA, especially for poor maize farmers who cannot afford N fertiliser.

Application of Conservation Agriculture Principles for the Management of Field Crops Pests

Worldwide, farmers are called upon to abandon harmful pesticides and adopt conservation agriculture for improving environmental sustainability, soil fertility, pest management and farm profits, among other benefits. Whereas the positive environmental benefits of conservation agriculture are non-questionable, pest management benefits are still a subject of debate. Abandonment of the plough and harmful pesticides towards conservation agriculture presented new challenges to farmers in terms of pest management. Pest problems are frequently reported as the main yield limiting factor for conservation agriculture in many production systems of the world, especially among the resource poor farmers. Here we first review the pest management benefits of conservation agriculture principles, with special focus on weeds and animal pests. In conservation agriculture, emphasis should be placed on use of different multiple and varied tactics incorporated into the cropping system design to avoid damaging levels of pests, thus minimizing the need for curative solutions. Conservation agriculture embraces integrated pest management, as it aims to incorporate reduced pesticide applications with cover crops, conservation tillage and crop rotation to strengthen natural pest control. We show that effective long term weed management in conservation agriculture systems is based on an integration of measures for limiting competitiveness of the weeds that are already in the field and growing with the crop, preventing the introduction of new weeds, and preventing the multiplication of the weeds that are already there. Although the abandonment of tillage towards no-till requires an initial investment on herbicides for weed control, herbicide requirement tends to decline over time with proper application of conservation agriculture. Proper selection of planting date, density and spatial arrangement of a crop can maximize the space it occupies early in the season and put competitive pressure on weeds. Crops can be rotated in sequences that are not only profitable, but highly effective at breaking animal pest cycles. Mixed cropping reduces pest populations by increasing environmental diversity and lowering the overall attractiveness of the environment. We then highlight some possible solutions to the major challenges for pest management through conservation agriculture practice. Promotion of integration of conservation agriculture principles with cultural measures is essential for pest management in conservation agriculture systems. In conservation agriculture, it is important for farmers to employ several strategies simultaneously so that if one strategy fails, then the other ones operate to prevent yield loss. The focus should not be just on how to fit various pest management tactics into the conservation agriculture production system, but also on how the system can be modified to accommodate various pest control tactics. We demonstrate that farmers practicing conservation agriculture have several cultural methods that they can put together to build up a good pest management strategy. Although cover crops and mulches are generally viewed as the first line of defense against weeds, the reduction in weeds is not enough to eliminate the need for chemical control. Cover crops can be used to reduce animal pest dispersal, colonization and reproduction on crops through maintenance of the cover crop as a sink for various pests, confusing the pests visually and by causing microclimate changes that reduce pest success. Fertilizer timing and placement strongly influences crop competition; and deep banding of fertilizer has the potential to enhance not only fertilizer use efficiency, but also crop resistance to animal pests and competitive ability against weeds. Proper selection of planting date, density and spatial arrangement of a crop can put competitive pressure on weeds and break animal pest cycles. Sanitation practices are important tools in conservation agriculture because of their ability to eliminate necessities that are important to the pests’ survival. The development of pest resistance will likely be minimal if host plant resistance is integrated with other control measures through conservation agriculture practice. A more holistic, integration approach of control tactics in conservation agriculture, which goes beyond the three principles, is essential for effective pest management.