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Mixed farming systems are likely to make an increasing contribution to meeting food demand in developing countries in the foreseeable future, and the impact of these systems on the environment has provided the focus for this particular study. The Terms of Reference for the study requested the identification of indicators which could be used to measure the impact of these systems on the environment, both technically and socio-economically. In addition, this report analyses the interactions between crops and livestock as part of the process of identifying those quantifiable indicators.

Global livestock production systems were classified into eleven groupings, as the basis for the study. Six of the groupings are characterised by significant crop-livestock interactions. Ruminants are the major livestock species interacting with cropping, providing power and nutrients to improve soil fertility. Under many mixed farming circumstances the keeping of livestock allows for the accumulation of capital for investment or risk-avoidance. During times of drought, livestock provide the only means of survival and are sold or exchanged for staple foods. Ruminants can also utilise resources such as crop residues, which might be wasted in the absence of animals. Crop residues are a major source of nutrients in the dry season, and can reduce the grazing pressure on rangeland.

The potential positive environmental impacts accruing from crop-livestock interactions are many. Draught animals can assist farmers to improve tillage and introduce soil conservation practices; operations that are unlikely to be undertaken with hand-cultivation. The lower compaction resulting from land preparation using animal traction, compared to tractor ploughing, also reduces the erosion hazard. The use of renewable animal power instead of non-renewable fossil fuels and tractors has reduced carbon dioxide and carbon monoxide emissions into the atmosphere. The supply of manure can be a major benefit of crop-livestock integration, and is often the only means of maintaining organic matter levels and sustaining soil fertility in cropping systems in developing countries. Livestock can provide “entry-points” for practices that promote sustainability, such as the introduction of improved forages into annual crop rotations and plantation agriculture. Forages, particularly legumes, make important contributions to soil fertility and erosion control, as well as providing feed of high nutritional value.

However, competition in resource use between crops and livestock can occur with potential negative effects on the environment. Of particular concern is the extension of dryland cropping into marginal lands and fragile ecosystems. Grazing areas can be reduced and the situation further aggravated if animal stocking rates are maintained or increased. Examples of major land degradation, initiated by an expansion of cropping, are given for China and Syria. Increases in irrigated cropping have also resulted in declining land productivity through salinisation and water logging. The impacts of land competition on vegetation, wildlife, soil conditions, water resources and socio-economic factors are discussed in some detail. Any re-allocation of crop residues away from their use for soil conservation purposes can also have negative environmental implications. Crop residues are important for mulch and compost, and are effective in reducing wind erosion. Competition may also exist for labour availability. Measures to mitigate the potential negative impacts of crop-livestock interactions are described.

Only indicators that can be used realistically to assess the local impacts of livestock on the environment are highlighted. For vegetation, these indicators are botanical composition, the number of trees and shrubs, and the amount of bare ground. Suggested indicators for soils are bulk density, organic carbon, total nitrogen, available phosphorus, cation exchange capacity and, in irrigated systems, electrical conductivity. Nitrate content, bacterial numbers and the presence of coliform organisms are indicators of water quality. Standards are given for these indicators. Detailed socio-economic indicators are described for land competition, crop residue competition, the competition for labour availability, the negative impacts associated with the introduction of draught power and the positive impacts of the intensification of agriculture.

The final section describes methods of measuring both technical and socio-economic indicators. The bibliography contains 120 references.

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