Livestock in crop land . Most of the world's agriculture is mixed crop-livestock farming, which covers about 2,500 million hectares of land. Throughout the world, animal numbers are growing but it is in the humid and sub-humid regions that growth is most rapid. Irrigated mixed farming systems, especially in the humid regions of Asia, have shown the greatest increase in productivity. Mixed farming makes very efficient use of natural resources.
Crop residues feed the animals and the animals' manure fertilizes the soil.
By keeping livestock, farmers add value to low value or surplus food, use labour more efficiently and diversify risk. By adding manure to the fields, not only are nutrients recycled but the improved soil structure reduces erosion. But the delicate balance between crops and livestock can be easily upset. In many tropical highland areas, human population growth is fragmenting farm sizes to the point where mixed farming systems are collapsing. One solution here is to increase access to outside inputs, such as animal feed and fertilizer, to maintain the nutrient balance.