Agroforestry is a land management practice that combines the planting and management of trees and shrubs with crops and pasture, providing benefits of soil health, crop yields, resilience to climate change, biodiversity and economic opportunities. Agroforestry encompasses numerous practices, including silvo-pasture, agro-silvo cultural, and agro-silvo-pastural. One successful agro-silvo-cultural practice is alley cropping, where the farmer plants rows of trees, shrubs or hedges between crop rows. Usually hedges comprise leguminous plants intended to fix nitrogen in the soil and provide leaf litter and prunable biomass. The hedges are pruned with the pruned material spread on the ground, to reduce shading and competition with the primary crop. Timing of pruning is important to ensure that the pruned biomass releases nutrients to the soil at a time when the primary crop needs them for maximum crop productivity; e.g. when alley-cropping maize, the pruned biomass needs to breakdown with and release beneficial nutrients into soil from two and eight weeks after planting the maize crop. This approach has proven to be highly successful, with examples in Malawi where gliricidia was alley-cropped with maize where the prunings created a three-fold increase in maize production, which was increased a further 29 % when fertilisers were added. This fertilisation could be achieved with green manure, and other climate smart soil amendment approaches. The space and number of hedge rows to primary crop is dependent upon the field size and the regular growth height of the shrub/hedge. The hedge must not be planted so close that it shades the primary crop. In larger fields, larger deep-rooted timber trees can be planted between groups of rows of primary crop, providing soil benefits, reducing wind-speeds/erosion, and providing timber products.
This approach is considered climate smart as it increases productivity, provides a mechanism for more climate resilient farming, whilst increasing soil carbon levels.
While agroforestry practices are deemed highly beneficial and climate smart, it is important to ensure that proposed practices are appropriate for the specific context – the benefits of the agroforestry practice match the needs of the farmer - and are fit for purpose. Obtain advice from an agroforestry expert before embarking on secondary crop/hedge species selection.
To effectively implement alley-cropping the following should be carried out:
- Step 1: Clearly understand the objectives of the intervention and identify an appropriate species for intercropping. For maize and sorghum in a smaller subsistence farm setting, selection and growth of hedge rows of a legumes such as cowpea or Gliricidia can provide sustainable benefits in terms of soil quality and secondary fodder/food products. In larger fields, timber trees can be planted every five to ten crop rows, depending on the height of the mature tree, and the shade-tolerance of the crop.
- Step 2: Identify and understand key conditions, such as prevailing wind direction, and sunlight to ensure that the field is planted in an appropriate configuration, with primary crop and secondary (hedge/shrub/tree) crops planted in such a way as to benefit the primary crop and not compete with it. East to west row orientation should maxmise sunlight, topography permitting.
- Step 3: For beneficial hedgerow growth with legume species such as Leucaena, cliricidia, and Sesbania sesban, the trees should be planted in rows between two and four metres apart, with individual trees planted as close as possible - between 10 to 15 cm apart. If planted closely, the trees will favour leaves over step growth, creating more mulch to prune for cover. Note that if rows are planted too closely, the secondary crop can dominate the available crop land reducing productivity. Furthermore, the closer the hedges, the more shade will present, which can depress crop growth, and also start to compete for soil water and nutrients, which is not beneficial.
- Step 4: Once reaching sufficient maturity, after approximately six months (one-metre tall for legumes)– hedges should be pruned to generate mulch for working into the soil. Then the primary crop (maize) can be planted. Pruning once per month thereafter provides cover and ensures that light penetration is maintained. Planting legumes approximately six months before planting the primary crop can ensure that sufficient pruned material is available to incorporate into the soil to enhance growth.
- Step 5: After harvesting the primary crop, hedgerows can be left to grow taller so that shade reduces weed grown, and to develop material to prune and incorporate into the soil again during the following crop cycle. However, hedges should not be allow to grow too high or dense as their roots will dominate the soil and out-compete primary crops for water and nutrients.
Before implementing any of these technologies, further research may be required beyond the guidance provided here. The World Agroforestry Centre (ICRAF) has many resources, toolkits and success stories that can support such research.
- The Food and Agriculture Organisation (FAO), 2015. Agroforestry Definition. Rome, Italy.
- FAO, 2013. Agroforestry, food and nutritional security. Rome, Italy
- Muschler, R.G. 2016. Agroforestry: Essential for Sustainable and Climate-Smart Land Use. Chapter in: Pancel L, Köhl M (eds.) 2016. Tropical Forestry Handbook. 2nd ed. Springer-Verlag. Pp. 2013-2116. 2 Volumes. 3633 pp.
- Rahman, S., 2018. Agroforestry: Why don’t farmers plant more trees? Forest News Website. CIFOR
- University of Missouri Centre for Agroforestry, 2015. Agroforestry Academy: Chapter 3: Alley Cropping. University of Missouri, Columbia, Missouri, USA.
Benefits
- Trees, shrubs, and hedges are incorporated into farming systems and have many different biophysical and socio-economic benefits.
- Use of leguminous hedges no only provides pruned materials to provide cover, but they also help fix nitrogen in the soil.
- Hedges planted in alleys can also provide other benefits such as edible seed pods for human or animal consumption.
- Hedges and trees can reduce soil erosion from run-off or wind erosion.
- Alley cropping can provide opportunities for diversified income – selling secondary crops and/or timber.
- Alley cropped timber trees can provide building materials fire wood.
Drawbacks
- Initial labour requirements will likely be significant; however, this will be primarily at the earlier stages of the intervention.
- Ongoing maintenance such as pruning and maintenance of hedges will be needed, although relatively minimal.
- There may be some costs involved in obtaining hedge seedlings.
- Use of trees rather than hedges and shrubs introduces more labour, but yields more benefits.
