Residue Retention and Mulching in CF

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1 Residue Retention and Mulching in CF These are two different things Residue Retention is achievable Mulching, much less so Residue Retention Mulching Residue Retention Maximize soil cover by retaining crop residues to the extent possible Mulching Cutting, importing and laying biomass such as grass, from surrounding areas

2 Mulching Uganda - importing biomass Uganda - Incomplete mulching Maximizing ground cover is a key aim of CF and the benefits are unquestioned but encouraging the importation of biomass to achieve this on any meaningful scale involves excessive labour inputs and is beyond the reach of most farmers. Where farmers crop several hectares or above mulching is impossible.

3 Mulching In Uganda early CF adopters on a new project supported by the CFU mistakenly assumed that mulching as opposed to residue retention was an obligatory requirement. The outcome of a 10 day field visit which included interviews with many farmers and measurements of areas where mulching had been attempted was as follows: Labour Inputs: Complete mulching of crop inter-rows depending on distance to source of mulch was between 40 to 60 SPD s/ha. Costs: Where labour was hired to cut, carry and lay mulch depending on the source, the cost was between $24 to $59/ha. None of the farmers visited had completed mulching the fields they had converted to Min-Till, all remarked on the excessive costs and/or work involved, and suggested that the requirement was putting off potential adopters. Heavy mulch may suppress early weed growth but secondary weeds that emerge through the mulch are difficult to eradicate by hoe weeding.

4 Mulching Conclusion: Mulching small vegetable gardens is sensible and commonplace, but is not transferable to field scale rain-fed agriculture and where seen, is often linked to incentives such a subsidized inputs and is restricted to small demonstrations plots.

5 Residue Retention Regions of Bi-modal Rainfall and Controlled Grazing In areas of Kenya, Tanzania, Uganda and elsewhere where bi-annual cropping and controlled grazing are practiced, farmers who convert from overall soil inversion to Min or Zero Till should experience a rapid build up of crop residues and achieve adequate ground cover. Regions of Mono-modal Rainfall and Communal Grazing In these countries including Zambia, Zimbabwe, Malawi, South Africa etc. substantial difficulties confront the achievement of 25%-30% permanent soil cover throughout the dry season. Challenges are highlighted in the following slides:

6 Burning Residues Residue Retention Challenges Kenya Zambia In many African societies burning of crop residues is a deep rooted tradition. The CFU has had considerable success in persuading farmers that no-burning is CF non-negotiable. Nevertheless, burning remains commonplace and fires lit intentionally or accidentally often spread from adjacent farms.

7 Burning Residues AFRICA ACTIVE FIRE DETECTIONS FEBRUARY AND AUGUST 2004 February August

8 Burning Residues Zambia September Colloids from indiscriminate burning obstruct view of land at low altitude

9 Communal Grazing Hoe MT & good early season cover of Maize residues Communal grazing after the harvest Maize crops of 4 tons/ha and above produce large amounts of residues but in areas where communal grazing is practiced after the harvest, all but the largest stalks will be removed. Of the 9 Provinces in Zambia communal grazing occurs in Southern, Central, Eastern and Western, but particularly Southern, where the cattle population exceeds 1,000,000 animals.

10 Annual Rainfed Crops and Residues Maize and other Cereals: Maize residues after harvest 5 ton/ha crop Termite action Cereals produce the most residues, with 100% ground cover achieved from high yields immediately after harvest. During the extended dry season in central and southern Africa (6 to 7 months), termite activity will reduce residues significantly but 20% to 40% cover at the onset of the following rains is achievable. Due to the complexity of the subject, uncertainty still exists regarding the influence of termites on the accumulation or depletion of SOC and the spatial distribution of these effects in soil profiles.

11 Annual Rainfed Crops and Residues Cotton: ADP MT ripping through Cotton Residues Cotton residues in young Groundnut crop Cotton crops yielding over 1 ton/ha produce a reasonable amount of woody residues which may be reduced by termite action but are not consumed by cattle and can provide some ground cover throughout the dry season.

12 Annual Rainfed Crops and Residues Sunflower: Groundnuts: Modest cover not favoured by cattle Negligible Soya Beans: Negligible In regions of mono-modal rainfall, grain legume residues including Groundnuts, Soya Beans, Cowpeas and Sugar Beans disintegrate early in the dry season leaving few if any residues. Accumulation of organic carbon in top soil from natural incorporation of small amounts of residues may be negligible but any surface material that inhibits the velocity of storm flow across fields, will reduce sheet erosion and improve infiltration of rainfall.