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Chapter 3: Mixed farming systems & the environment

Environmental challenges
Mixed farming systems in the developing world: Nutrient deficits
Mixed farming systems in the developed world: Nutrient surpluses

Mixed farming systems & the environment

MIXED FARMING systems, the largest category of livestock system in the world, cover about 2.5 billion hectares of land, of which 1.1 billion hectares are arable rainfed crop land, 0.2 billion hectares are irrigated crop land and 1.2 billion hectares are grassland. Mixed farming systems produce 92% of the world's milk supply, all buffalo meat and approximately 70% of the sheep and goat meat (Figure 3.1). About half of the meat and milk produced in this system is produced in the OECD, Eastern Europe and the CIS, and the remainder comes from the developing world. Over the last decade, meat production from this system grew at a rate of about 2 percent per year and thus remains below global in demand.

Environmental challenges

The evolution of the mixed farming system

Mixed farming is probably the most benign agricultural production system from an environmental perspective because it is, at least partially, a closed system. The waste products of one enterprise (crop residues), which would otherwise be loaded on to the natural resource base, are used by the other enterprise, which returns its own waste products (manure) back to the first enterprise. Because it provides many opportunities for recycling and organic farming and for a varied, more attractive landscape, mixed farming is the favourite system of many agriculturalists and environmentalists.

In many situations crop and livestock production is largely in balance with nature. There are important exceptions, such as some mixed farming systems of the tropical highlands of Asia and Central Africa which, partly because of overgrazing, are amongst the most eroded and degraded systems of the world. On the other end of the development spectrum, heavy use of feed and fertilizer in the industrial world and in some of the fast growing economies of East Asia, has led to nutrient loading, habitat destruction and water pollution. In this context, it has to be remembered that integrating crops and livestock neither generates new nutrients (with the exception of nitrogen fixation by leguminous plants) nor reduces nutrient surpluses.

Figure 3.1: Share (%) of global production produced by mixed farms.

In order to understand the environmental impact of livestock it is important to understand how mixed farming systems evolved. A brief description follows.

The evolution of the mixed farming system

As rural population pressure increases, both crop and livestock farmers need to intensify production. McIntire et al., (1992) show that, as population pressure increases, the two activities often become integrated. Traditional soil protection techniques, in particular the long fallow periods which protected against erosion and allowed soil nutrients to recharge, are no longer possible (Kjekshus, 1977). If farmers cannot resort to external inputs, the integration of livestock and crop activities represents their main opportunity for intensification. Mixed farming has therefore become the basis for modern agriculture. Mixed farming systems provide farmers with an opportunity to diversify risk from single crop production, to use labour more efficiently, to have a source of cash for purchasing farm inputs and to add value to crops or crop by-products. Combining crops and livestock also has the potential to maintain ecosystem function and health and help prevent agricultural systems from becoming too brittle, or over connected, by promoting greater biodiversity, and therefore increased capability to absorb shocks to the natural resource base (Holling, 1995).

Environmentally, mixed farming systems:

• maintain soil fertility by recycling soil nutrients and allowing the introduction and use of rotations between various crops and forage legumes and trees, or for land to remain fallow and grasses and shrubs to become reestablished;

• maintain soil biodiversity, minimize soil erosion, help to conserve water and provide suitable habitats for birds;

• make the best use of crop residues. When they are not used as feed, stalks may be incorporated directly into the soil, where, for some time, they act as a nitrogen trap, exacerbating deficiencies. In the tropical semi-arid areas, termite action results in loss of nutrients before the next cropping season. Burning, the other alternative, increases carbon dioxide emissions; and

• allow intensified farming, with less dependence on natural resources and preserving more biodiversity than would be the case if food demands were to be met by crop and livestock activities undertaken in isolation.

Under different sets of pressures and opportunities, several developments are possible, depending on resource endowment and market access. Initially, and if market opportunities open up, the symbiosis between crops and livestock can intensify (Christiaensen et al., 1995 and Box 3.1), and the nutrient balance can be maintained. This chapter's case study (Box 3.6) on the long term evolution of a mixed farming system in the semi-arid regions of Kenya illustrates this development.

Box 3.1 Population pressure and the evolution of the cassava-livestock system in sub-Saharan Africa.

POPULATION PRESSURE and the evolution of the cassava-livestock system in sub-Saharan Africa. A comparative analysis of cassava-livestock interactions in six countries, covering seven regions in sub-Saharan Africa, clearly shows that as population intensity increases, crop-livestock interactions intensify as organic fertilizer and the use of cassava as a livestock feed gain importance. For example, in the densely populated areas of Nigeria, between 77 and 100 percent of the animals were fed farm-grown cassava, whereas in the sparsely populated areas of Zaire and Tanzania, this varied between 8 and 50 percent. Livestock thus help to conserve a better nutrient balance within the system, and reduce the threat of nutrient loss.

Source: Christiaensen et al., 1995.

If pressure increases further, crop-livestock systems can separate into specialized crop or livestock activities. If there are no improved market opportunities, which is the case in many developing countries, and as human population pressures continue, the arable land part of the system will experience increased rates of nutrient depletion (and therefore flora and fauna biodiversity loss) and soil erosion. This can, in turn, lead to a downward spiral of mono-culture with lower quality food crops, increased under-nutrition and famine (Cleaver and Schreiber, 1994). This development path is illustrated in this chapter's case study on Rwanda in Central Africa (Box 3.4).

However, if urban incomes rise, more market opportunities open up and farmers become more integrated into the market economy, allowing them to specialize, take advantage of economies of scale and develop greater levels of expertise. Finally, under very strong demand, and often encouraged by input or price subsidies such as exist in many developed countries and in the fast growing economies of East Asia, excessive importation of nutrients can lead to soil and water tables being overloaded with nitrogen or phosphorus. The case study on Brittany in France illustrates this condition (Box 3.7).

The challenge for the mixed farm sector will therefore be to maintain a nutrient and energy equilibrium through crop-livestock integration and at the same time allow sustainable productivity growth. The mixed farming system, more than any other production system, operates under a wide range of environmental and economic conditions and requires regional solutions and practices. However, there is one overriding criteria in determining the size and nature of the system's impact on the environment, and this is the nutrient balance. This balance is determined by the nutrients (N. P and K) brought into the farming systems by inorganic fertilizer, feed, nitrogen fixed by leguminous plants and transfer from grazing areas outside the farm, and the amounts exported in animal products or lost from the land to the air or groundwater. A positive balance of nutrients will have a completely different effect (and will require different measures) than a nutrient deficient system. In this analysis, the mixed farming systems are classified either as nutrient deficient systems, which occur mainly in the developing world, or as nutrient surplus systems, mostly found in the industrialized world and increasingly in the fast growing economies of East Asia.

Mixed farming systems in the developing world: Nutrient deficits

Driving forces
Response: Technology and policy options

The mixed farming systems of the developing world contain about 67 percent of the cattle and 64 percent of the small ruminants of the world. Throughout the world, animal numbers are growing in the mixed farming system, most rapidly in the humid/sub-humid regions (Annex 2). Sheep and goat numbers show the fastest growth rates in the humid/sub-humid region, underlining how human population pressure is reducing farm size and access to and use of resources.

Irrigated mixed farming systems have shown the greatest increase in productivity, particularly in the humid regions of Asia. This is clearly a result of the strong growth in demand for animal products and better access to feed resources and other types of infrastructure in Asia. Milk production is important, particularly in south Asian countries, due to the growing demand in the region and the favorable policies that many governments have created for the dairy sector. Although the growth of dairy production can place more pressure on land resources, it can also increase the use of crop by-products which in turn improves nutrient recycling and, if of high quality, can diminish methane production.


There is a considerable range of positive and negative interactions between livestock and the environment within the different sub-systems. These interactions can affect land quality in its physical (soil erosion) and chemical properties (soil fertility), the use of nonrenewable resources, such as fossil fuels and fertilizer, and the conservation of agricultural (plant and animal) biodiversity. They are detailed below.

Soil erosion is probably the most pervasive form of land degradation in the developing world. Erosion rates are particular high in Asia, Africa and South America where they average 30 to 40 tons/ha/year, compared with an average soil formation of 1 ton per ha/per year (Pimental et al., 1995). In Africa, 60 percent of soil erosion damage occurs in the semi-arid and dry sub-humid regions where cropping and livestock co-exist (Thomas and Middleton, 1994), with strong interlocking factors of cropping, fuelwood collection and grazing.

Soil erosion is even more damaging on sloping lands. Poorly managed sloping terraces under crops and degraded rangelands can lose up to 100 MT/ha/year. Conversely, well managed pasture land loses 7 MT/ha/year or less and well managed forest land losses range from 0-10 MT/ha/year. Bojo and Cassells (1995) quantified these losses in the degraded Ethiopian Highlands (Box 3.2). Their results showed the effect of including pastures in those environments as a means of reducing erosion.

Box 3.2 Effect of soil erosion and nutrient export on mixed farm productivity in Ethiopia.

Soil losses

Grazing systems

5t/ha/) ear

Crop land


Crop production losses

500,000 ton

Livestock production losses

1000,000 TLU

Gross Annual

US $ 100 million

Immediate Losses

Gross Discounted

US $1.9 billion

Cumulative Losses

The nutrient export results from the use of dung an crop residues as fuel.

The Gross Discounted Cumulative Loss captures the cumulative nature of the land degradation, in which each year's erosion and nutrient loss is followed by another adding layers of losses and hence cost on top of each other

Source: Bojo and Cassells, 1995.

Soil fertility. Livestock play a significant role in maintaining soil fertility. In partially closed mixed farming systems, livestock can replenish a substantial share of soil nutrients, and therefore reduce the need for inorganic fertilizer, with corresponding savings for farmers in terms of cash outlay, for the country in foreign exchange, and for the world in non-renewable resources. The total value of this contribution is not known, although approximate figures are given by Jansen and de Wit (1996) for the irrigated mixed farming systems of Asia. Assuming manure production of about 1 ton dry material per year per Tropical Livestock Unit1, and an effective availability2 of 15 percent of the nutrients in the case of stall fed and half that amount for grazing animals, the amount of nutrients under stall fed conditions is about 8 kg N and 6 kg P per year per TLU.

1 A Tropical Livestock Unit (TLU) is an animal unit used to aggregate different classes of livestock. One TLU equals an animal of 250 kg liveweight.

2 The balance is lost through evaporation, leaching and, in many arid areas, through use as fuel.

Under those assumptions, livestock in the mixed irrigated farming system can supply between 2 and 10 percent of the nitrogen requirements for rice, and about 40 to 120 percent of the requirements for phosphorus in cassava (Table 3.1).

As can be clearly seen from Table 3.1, nitrogen is the most depleted nutrient, with the amount lost varying, depending upon the technology used in collection, storing and application practices. How farmers approach these three factors largely determines the effectiveness of the recycling process and therefore provides an avenue for intervention. As shown, stall feeding significantly increases the amount of nutrients available from manure.

To demonstrate the importance of these contributions, an estimate was made of the amount of fertilizer that would be required to replace the manure that is used in the irrigated system of the humid tropics. The value of this is estimated to be between US$ 700 to US$ 850 million per year, depending on various assumptions (Table 3.2).

The economic benefits of improved soil structure as a result of adding soil organic matter from manure are more difficult to estimate. Adding manure to the soil increases cation exchange capacity, and improves soil physical conditions by increasing the water-holding capacity and improving soil structure stability. When adding the manure output from pigs and ruminants together, livestock may contribute up to 35% of the soil organic matter requirements. This is a crucial contribution because this is the only avenue available to many farmers for improving soil organic matter.

Non-renewable resources. Draught animal power, in addition to other economic benefits, provides an important source of energy in the mixed farming systems of the world and helps to reduce dependence on nonrenewable fuel resources. In developing countries, animal power is used to cultivate about 52 percent of the 480 million hectares of cropland (FAO, 1994). Draught animals provide between 25 to 64 percent of the energy needed for cultivation in the irrigated systems of the world. Worldwide 300 million draught animals are used in small-scale agriculture, while 30 million tractors would be needed to make the same contribution. This is equivalent to an US$ 200-300 billion investment in tractors plus a $5 billion annual fuel cost. Assuming that approximately 50 percent of the arable land is cultivated in the world's irrigated areas with draught animal power, complete replacement by tractors would require annually 888 million litres of diesel at a cost of US$ 222 million, and US$ 429 million for depreciation of the equipment (Jansen and de Wit, 1996).

Table 3.1: Estimated contribution of livestock to crop nutrient requirements in irrigated systems in Asia (% N and P removed by crops).

































Assuming rice yields of 4 tons per ha, and cassava yields of 10 tons Per ha

Source: Jansen and de Wit, 1996.

The value of animal manure for cooking fuel is more controversial. Dung cakes are the main source of household energy for millions of poor households in the developing world. It is often argued that using dung for fuel removes soil nutrients and therefore carries high opportunity costs (Mearns, 1996). However nitrogen is the only major nutrient that is lost because the remaining ash is high in phosphorus and potassium.

Biodiversity. In mixed farming systems, livestock-environment interactions can be a key focal point. As human population pressures increase, some types of wildlife or plant diversity can be lost while other types of biodiversity may actually increase. Reid et al. (1995) demonstrate how the number of tree, bird and mammal species changes as human use of the resource base intensifies (Figure 3.2).

These results are important for demonstrating the dynamic nature of ecological systems. They also show that man's agricultural activities must be balanced with the environment's capacity to sustain them.

An often overlooked component of biodiversity is soil micro-flora and fauna. Arthropods, with 90 percent of all species, dominate biodiversity (Pimental et al., 1992). For example, in a New York alfalfa "ecosystem" Pimental et al., (1992) reported 600 species of above ground arthropods. Livestock and manure have a beneficial effect on this biodiversity. For example, in mixed farms in Japan, the species diversity of the micro-fauna under grass more than doubled when manure was added to the land (Kitazawa and Kitazawa, 1980).

Table 3.2. Amount and value of manure in fertilizer equivalents in Asia's irrigated areas.



Manure kg/ha



Fertilizer Equivalent (kg/ha)



Financial Value (US $/ha)



Total Economic Value (US $ mill)



Source: Jansen and de Wit, 1996.

Figure 3.2: Changes in biodiversity as human use intensifies.

In forest and communal grazing areas, adjacent to mixed farming areas, plant and animal biodiversity is decreasing because of over-grazing. There are many examples quoted in the literature confirming this trend, for example, in Syria, Rajastan, and West Africa. It is not clear, though, whether these are irreversible, long term changes. For example, Thomas and Middleton (1994) report that no systematic pattern of vegetation change could be detected in a 27 year vegetation survey of 77 villages in the Sudan. However, wildlife biodiversity is disturbed if land is fragmented and river sides are cultivated. Finally, the mixed farming areas of the world contain the main centres of domestic animal genetic resources (local livestock breeds) of the world. Urgent steps to safeguard that future capital are proposed in Chapter 5.

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