Date
22 Jan 2014
A viable option to avoid over dependence on fertilizers and pesticides in closing the yield gap in Africa is to ensure agricultural intensification occurs through natural and resource-conserving approaches such as agroforestry, say scientists in a special issue of Current Opinion in Environmental Sustainability due to be released in February 2014 to coincide with the 3rd World Congress on Agroforestry in Delhi, India.
Intensification – growing more on the same amount of land – is seen as key to increasing food production in Africa to meet the needs of a growing population. In many parts of Asia, this has been achieved through the use of greater inputs such as fertilizer, but it has come at a cost – causing soil degradation, loss of biodiversity and pollution which has impacted on food security and farm incomes.
“A long-term solution to intensification in Africa should not purely be based on an imported intensification model but instead consider approaches that can maintain the quality of the available resource base through ensuring nutrient cycling, organic matter build-up, biodiversity improvements and water quality regulation,” says Sammy Carsan, Tree Domestication Scientist with the World Agroforestry Centre and lead author of the article. “All this can be achieved through agroforestry.”
In the journal article, Carsan and colleagues put forward their case in a review of what is known about how agroforestry can regulate and enhance these drivers of ecosystem services to sustain agricultural intensification in Africa.
Crop production in Africa is seriously hampered by the degradation of soil fertility, water and biodiversity resources. Currently, yields for important cereals such as maize have stagnated at 1 tonne per hectare. Climate change and increasing demand for food, animal fodder and fuel is likely to exacerbate the situation.
“Closing the yield gap - the difference between observed yields and those which are possible in a given region – requires restoring nutrients that have been depleted,” explains Carsan. “Trees are able to enhance soil quality by adding above- and below-ground organic matter and by releasing and recycling nutrients.”
The article outlines how agroforestry practices involving the use of legumes in rotations or intercrops can restore soil nutrients by fixing nitrogen, improving soil organic matter and reducing reliance on fertilizer use. Analysis over a 5-year cycle showed that net profit from unfertilized maize was US $130 per hectare compared to US $269 and US $309 for maize intercropped with Gliricidia or in rotation with Sesbania, respectively.
Examples are given of how integrating trees into farms can create diversified and productive systems that provide farmers with both staple foods and marketable tree products across seasons, as well as store carbon. There is also evidence to show that diversity is associated with greater ecosystem resilience.
In Niger, the practice of Farmer Managed Natural Regeneration – which involves farmers selectively managing trees such as Faidherbia albida on their land – has supplied fuelwood, fodder and food, and has led to the re-greening of 5 million hectares since 1985. Faidherbia has been reported to increase maize yields from 1 to 2 or 3 tonnes per hectare in parts of Africa.
In terms of biodiversity conservation, agroforestry systems for cocoa, coffee and rubber have a significant role in providing habitat for biodiversity in Africa in the wake of severe deforestation. In addition, trees host pollinators that are needed to fertilize cash crops.
“It is possible – with the right management – to conserve biodiversity and improve yields,” says Carsan.”
Agroforestry has also been shown to influence water regulation. A study into agroforestry systems that intercrop Gliricidia sepium with maize in Malawi showed improved water filtration and water use efficiency as compared to systems where maize was grown by itself.
Experiences from temperate agriculture indicate that the use of vegetative strips can reduce the flow of agrochemical pollutants, increase infiltration and reduce runoff as they hold soil in place and reduce susceptibility to erosion.
The authors highlight how agroforestry not only retains ecosystem functions but is well-suited to meeting development needs in Africa. They point out, however, that further research is needed to integrate ecological knowledge with an understanding of socio-economic constraints so that agroforestry can fulfil its potential in improving productivity, enhancing ecosystem function and providing adaptability in different farm settings.
Download the full article:
Carsan S, Stroebel A, Dawson I, Kindt R, Mbow C, Mowo J, Jamnadass R. (2014). Can agroforestry option values improve the functioning of drivers of agricultural intensification in Africa? Current Opinion in Environmental Sustainability 6: 35-40
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This article appears in a special issue of the journal Current Opinion in Environmental Sustainability on the theme ‘Sustainability challenges.’ The full special issue is available Open Access at http://www.sciencedirect.com/science/journal/18773435/6/supp/C
The issue will be launched during the World Congress on Agroforestry in Delhi, India in February2014.