Addressing the Causes of Land Degradation, Food/Nutritional Insecurity and Poverty: a New Approach to Agricultural Intensification in the Tropics and Subtropics

by Roger RB Leakey, Agroforestry and Novel Crops Unit, School of Marine and Tropical Biology, James Cook University, Cairns, Australia.

Photo 1: A multifunctional agriculture landscape in Viet Nam with many income-generating
tree-based production systems on hillsides surrounding an area of intensive food production
on the most fertile soils.


The shortage of new land for agriculture and the poverty of smallholder farmers in the tropics are serious constraints on the expansion of modern intensive agriculture to overcome the food crisis. Consequently, there is an urgent need for both the rehabilitation of degraded farmland and for the realization of new income-generating opportunities. This paper presents a tried and tested award-winning (Equator Prize) three-point action plan using biological nitrogen fixation and a “new wave” of crop domestication focusing on marketable and highly nutritious traditional foods. If widely adopted, this package could fill the yield gap of crops such as maize, thereby promoting new livestock enterprises and satisfying global food demand to 2050. It could also create new business and employment opportunities in diversified local rural economies and perhaps help expand agribusinesses.

The Green Revolution enabled a considerable increase in the productivity of conventional high-input agriculture, thereby saving millions of people from starvation. However, this achievement came at a high cost to the environment as a result of land conversion through deforestation, land degradation and the overexploitation of natural resources, especially soil and water. It is now also recognized as being a major contributor to climate change. Furthermore, despite the improved productivity of major food staples, there are still billions of people suffering from poverty, malnutrition and hunger. Consequently, there have been many calls for a new approach to food production, especially in the tropics and subtropics where the problems and issues are the most urgent and prevalent. The key issues to be addressed are land rehabilitation, food and nutritional security, and income generation – all within sustainable land-use practices. The overriding questions are: How can the land be used to feed a growing population without further damage to the local and global environment?’ How can food and nutritional security be achieved on a declining area of available land? And how can the land be used to enhance the livelihoods and incomes of the rural poor?

Answers to these questions fall into two main camps: there are some who believe that the only way forward is by intensifying the high-energy-input Green Revolution model involving further productivity improvements through research and breakthroughs in crop and livestock genetics; others think that more ecologically based approaches involving low-input agriculture are the way forward. To consider the merits of these two contrasting and highly polarized views, we look at the environmental and socio-economic problems arising from land conversion to agriculture, and offer some solutions.

Figure 1: The cycle of land degradation and social deprivation

Current land-use practices in the tropics have led to deforestation, overgrazing and overexploitation of soils and water resources (figure 1), causing a cascade of negative impacts: land degradation, loss of soil fertility, loss of biodiversity, the breakdown of agro-ecosystem function, declining yields, hunger and malnutrition, and declining livelihoods. Associated with these are reduced access to traditional wild foods, loss of income and the increased need for costly (often unaffordable) agricultural inputs. The response of proponents of intensive, high-input industrial farming is to redouble efforts to increase the yield of staple food crops by enhancing their capacity to withstand biotic and abiotic stress. This approach fails to recognize three important points: (i) since farmers are failing to grow staple foods anywhere near their existing biological potential, resulting in what is called the “yield gap” — the difference between potential yield per hectare and actual yield achieved by farmers (figure 2) — increasing the biological potential will not help; (ii) poor, smallholder farmers locked in a poverty trap cannot afford to buy the requisite fertilizers and pesticides (even if they had adequate access to them) that would allow them to practice monoculture agriculture; and (iii) the overriding dominance of starchy food staples in modern agriculture may provide adequate calories for survival, but they lack the proteins and micronutrients necessary for healthy living, not to mention the sensory pleasures provided by traditional and highly nutritious foods which used to be gathered from the forest. In addition, the widespread clearance of forests from the landscape, especially from hillsides, exposes soils to erosion and increases run-off, resulting in landslides and flooding that destroy property and lead to the death of large numbers of people. Loss of perennial vegetation also contributes to climate change.

Figure 2: A representation of the yield gap in agriculture, and the steps needed to close the gap

Therefore, an alternative approach to agricultural intensification is required. Indeed, several recent reviews of agriculture (IAASTD, 2009; Royal Society, 2009) and of issues relating to the role of agriculture in the global environment (e.g. Hassan, Scholes and Ash, 2005; GEO, 2007; CAWMA, 2007) have suggested that “business as usual” is no longer the appropriate option due to the scale of the problems and the constraints facing poor farmers. We need to go back to basics and look at the cycle of land degradation and social deprivation (figure 1). Clearly, a focus on crop yield is important, but, rather than trying to increase yield potential, we need to focus on closing the yield gap. In the worst cases, farmers growing maize are achieving only 0.5–1 ton per hectare when the potential is around 10 tons per hectare. In this situation, closing the gap could increase food production by 15- to 20-fold; but even if it were increased by only 2- to 3-fold, on average, this would be well over the 70 per cent increase that might be required to feed the 9 billion people predicted to populate the world by 2050, according to IFPRI (2011).

The primary cause of the yield gap is poor crop husbandry, which has a number of adverse effects, including loss of soil fertility and agroecosystem functions (such as the cycling of nutrients, carbon and water), impeding the operation of life cycles and food webs that maintain the natural balance between organisms, and reducing pollination and seed dispersal. Typically, soil nitrogen is the major constraint on crop growth in degraded soils. This can be restored by harnessing the capacity of certain legumes to fix atmospheric nitrogen in root nodules colonized by symbiotic bacteria (Rhizobium spp.). Numerous techniques have been developed to integrate appropriate legume species within farming systems. Probably the most effective and easiest to adopt are high-density improved fallows with species such as Sesbania sesban and Tephrosia vogelii or relay cropping with Gliricidia sepium (Cooper et al., 1996; Buresh and Cooper, 1999). Cultivating leguminous crops such as beans and peanuts can also contribute to this process. Together the legumes can increase soil nitrogen to a level that will produce maize yields of 4–5 tons per hectare within 2–3 years. This would help narrow the yield gap and greatly increase food security. However, this would not address the problem of the low levels of other soil nutrients, which means that the complete closure of the yield gap would require another approach involving the provision of inorganic nutrients, such as rock phosphate or chemical fertilizers, which have to be purchased. This necessitates income generation.

However, before addressing the need for income, it is necessary to find ways of restoring agroecosystem function. The legumes will start this process. For example, one of the more damaging weeds of cereal crops such as maize, millet and sorghum is Striga hermonthica. It is a root parasite on these cereals and its seeds germinate in response to root exudates from the young cereal plants. Interestingly, however, since Sesbania sesban and the fodder legumes Desmonium intortum and D. uncinatum also trigger Striga germination, they can be used to promote suicide germination in the absence of the cereal hosts (Khan et al., 2002). Desmodium spp. also acts as a repellent to insect pests of cereals, such as the stem borers Busseola fusca and Chilo partellus. Likewise, simple agroecological benefits can be attained by planting Napier grass (Pennisetum purpureum) as an intercrop or around small fields, as they attract the pests away from the crops (Khan et al., 2006).

The two interventions described above can therefore be used to restore soil fertility and initiate an agroecological succession, thereby rehabilitating farmland and reversing some of the land degradation processes. This may be considered as the first step towards closing the yield gap (figure 3).

Figure 3: . Procedures for closing the yield gap

The next step to a fully functional and more productive agroecosystem involves the integration of trees within the farming systems. Some trees are of course cash crops such as coffee, cocoa and rubber, which in the past were either grown as large-scale monocultural plantations or as a two species mix, such as cocoa under the shade of coconuts or Gliricidium sepium. Increasingly, however, they are becoming smallholder crops grown in much more diverse species mixing, such as bananas with fruit trees like mango, avocado and local indigenous trees that produce marketable products (Leakey and Tchoundjeu, 2001). This practice is well developed in Latin America and Asia, and is becoming widely recognized as a way to restore the biodiversity normally found in natural forests (Schroth et al., 2004; Clough et al., 2011). Certainly, the replacement of shade trees with trees which also produce useful and marketable products is a good strategy for farmers to enable them to maximize output from the land and minimize the risks associated with excessive reliance on a single crop species.

Photo 2: Intensive rice cultivation in the valley bottom, with hillsides planted with diverse
commercially important trees for income generation and environmental benefits. Indonesia
alone has about three million hectares of these “agroforests”.

There has also been another silent farmer-led revolution in the tropics, especially in South-East Asia. In Indonesia, in particular, many farmers who used to practice shifting agriculture have replaced the natural fallow with a commercial fallow (agroforest) based on tree crops (see photo 2). They grow rice in the valley floors and plant a wide range of useful and commercially important tree species among the other food crops which they have planted on the valley slopes (Michon and de Foresta, 1999). These trees become productive successively in later years, creating a continuous supply of marketable produce (e.g. cinnamon, tung nut, damar, duku and rubber) for several decades, often ending in a timber crop. This diversification of the farming system with perennial crops therefore achieves several important outcomes. It protects sloping land from erosion, improves water infiltration into the soil, sequesters carbon and so mitigates climate change, generates income, enhances biodiversity and promotes agroecosystem function. In other words, it performs all the functions that large-scale monocultures fail to do, and the livelihoods of the farmers are far better than those locked in poverty due to growing a failed maize crop in Africa, for instance. This approach to agriculture achieves high crop yields close to the biological potential on the best and most fertile land, and generates income from tree crops on the more marginal land, creating a land-use mosaic with many environmentally beneficial impacts (see Photo 1). Importantly, there is also some evidence that complex perennial vegetation, such as a natural forest or an agroforest, is better than a herbaceous crop at recycling moisture to the atmosphere that can be advected downwind to fall as rain. Thus agroforests are likely to be beneficial to rain-fed agriculture in dry and drought prone areas of the world.

In a further initiative, over the past 20 years agroforesters have sought to take this strategy to a higher level by starting to domesticate some of the very wide range of tree species which have been the source of locally important food and non-food products traditionally gathered from the forest (Leakey et al., 2005; Leakey, et al. forthcoming). The approach has been to apply well-known horticultural techniques of vegetative propagation for cultivar development (Leakey, 2004; Leakey and Akinnifesi, 2008). Unconventionally, this has been implemented at the village level as a participatory process with local communities, rather than on a research station (Leakey, Schreckenberg and Tchoundjeu, 2003; Tchoundjeu et al., 2006; Asaah et al., 2011). This participatory approach has been implemented to ensure that the farmers are the instant beneficiaries of the domestication, and that they are empowered by the development of their indigenous and local knowledge. Because wild populations of tree species contain 3- to 10-fold variations of almost any trait of commercial interest (Leakey et al., 2005), there is considerable potential for substantial improvements in characteristics such as fruit/nut size, quality and chemical content. This means that new, highly productive cultivars yielding good quality produce and the product uniformity required by markets is easily obtainable. Furthermore, because the multiplication process is implemented by vegetative propagation based on mature tissues with the capacity to flower and fruit, the long unproductive period usually associated with tree crops is circumvented, and trees become productive in 2–3 years.

Proof of concept has recently been demonstrated by the implementation of a participatory tree domestication project in Cameroon (Tchoundjeu et al., 2006, 2010; Asaah et al., 2011). In 12 years the project grew from four villages and a small number of farmers to over 450 villages with 7,500 farmers. The flow of benefits, such as income generation, started within less than five years (figure 4), and the farmers are reporting many other ways in which the project has also improved their lives (Asaah et al., 2011). Perhaps the most significant outcome has been the fact that young men and women in these communities now see a future for themselves by remaining within the community rather than migrating to local towns. In addition, the processing and value addition of produce from domesticated trees and other crops have been found to provide off-farm employment and to stimulate local enterprise and trade.

Figure 4: Income generated from tree sales by village nurseries associated with rural
resources centres in north and north-west regions of Cameroon after 2, 5 and
10 years (dollars). Source: Based on Asaah et al., 2011.

Historically, crop domestication has been implicated in the rise of civilizations that have become settled, politically centralized, socially stratified, economically complex and technologically innovative societies (Diamond, 1997). As the first wave of crop domestication primarily benefited the industrial countries of northern latitudes, it seems that the time is now ripe for a second wave of domestication to favour tropical and subtropical countries, which would enhance social equity and environmental rehabilitation worldwide (Leakey, 2011; Leakey and Asaah, in press).

The creation of new cash crops from the domestication of traditionally important, highly nutritious and useful species may be considered the second step towards closing the yield gap, because they can generate the income needed for the purchase of fertilizers and other agricultural inputs (figure 2). The trees can be used to enrich and improve the farming systems, whether by providing shade for commodity crops, or by forming agroforests on hillsides, orchards, field and farm boundaries, fodder banks or woodlots. However, farmers have many other competing demands for their money, including for local ceremonies, health care, children’s education, farm infrastructure and market transport. Consequently, the third step to closing the yield gap is to further expand the commercialization of these new tree crops, thus creating business opportunities and employment.

Most of the traditionally important products from tropical forests have been marketed locally for centuries. Over the past decade, an increasing number of these have been processed as new foods, and for use in medicinal, nutraceutical and cosmetic products, based on the fruits, nuts, gums, resins and fibres. Some of these have entered regional and international markets. However, the marketing and trade of commodities from tropical producers have often been exploitative. As a result, with the emergence of this new trade there has been a parallel initiative to ensure that the producers receive a fair price (see, for example, the Fair Trade Foundation at: In addition, ways have been sought to develop marketing partnerships aimed at the pro-poor commercialization of the traditionally important products derived from indigenous trees (Lombard and Leakey, 2010). These partnerships work to develop the products to a marketable standard and establish strong and viable trade associations that are forward thinking and market oriented. Through these partnerships it is possible to establish long-term relationships and supply agreements that ensure that the producers remain in the value chain.

Another aspect that deserves attention is the importance of livestock in agriculture. The 2020 projections of the International Food Policy Research Institute (IFPRI) suggest that 40 per cent more grain production will be needed and that more meat will be consumed by the world’s population. As mentioned earlier, grain production could be greatly increased by closing the yield gap. Recent developments have also demonstrated that fodder trees can be used to increase the productivity of cattle and goats. The integration of fodder trees and livestock into a farm is one of the elements of diversification that could be part of step 2.

Another recent development has been the establishment of public-private partnerships between multinational companies, national and international research teams and local producer communities, in order to promote and produce new products for international trade. Examples include Daimler AG in Brazil which is manufacturing components for the motor industry based on products from agroforestry systems produced by local communities (Panik, 1998), as well as Unilever plc. that is developing a new oil crop for margarine production with communities in Ghana and the United Republic of Tanzania using kernel oil from Allanblackia spp. (Jamnadass et al., 2010).

All of these developments offer a new approach to agriculture delivered by agroforestry practices (Leakey, 2010), which is more sustainable – environmentally, socially and economically – than current conventional approaches. This model conforms to the concepts of multifunctional agriculture promoted by the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD, 2009) which was ratified by over 60 countries in 2009.


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