In modern farming, crop and livestock production systems have become increasingly specialized (Entz et al., 2005) and often separate large-scale, specialized, energy-intensive farming operations (Kirschenmann, 2007). The recent concern over environmental quality of agricultural production has led to a renewed interest in crop–livestock systems, primarily because they provide opportunities for diversification, nutrient cycling and greater energy efficiency (Entz et al., 2005). Mixed systems enable the integration of different enterprises on the farm; livestock provide draught power and manure, while crop residues are fed to livestock. Deriving income from multiple sources (livestock and crops) offers farmers options for buffering crop failures or animal disease outbreaks (Carvalho de Faccio et al., 2007). The efficiency of mixed crop–livestock systems can be enhanced through the adoption of well-designed crop rotations, especially those incorporating a range of appropriate dual-purpose crops. These provide both food for humans and fodder for animals, often increasing overall farm productivity. In India, improved dual-purpose varieties of sorghum and millet have allowed smallholders to increase the milk production of buffalos and cows by up to 50% without reducing the grain output from their crops. Integrated crop–livestock zero tillage systems developed and implemented in Brazil are based on carefully planned crop and livestock combinations, resulting in increased yields while arresting further deforestation (Landers, 2007).
In the upland areas of the midlands of Sri Lanka, monoculture coconut systems were replaced by a diversified system combining tree crops (coconut and fruits), root crops and herbs with dairy cattle, goats and poultry, with the main goal of increasing farm income. The integrated system was economically viable compared with coconut monoculture, with dairy production and biogas covering domestic needs and contributing most to the total profits. The introduction of a mixed pasture, based on easily manageable Brachiaria subquadripara and Pueraria phaseoloides and the multi-purpose trees Gliricidia sepium and Leucaena leucocephala resulted in increases of 17% and 11% in nut and copra yield respectively. The system produced enough forage to maintain animal growth and production and the manure produced significantly improved soil fertility, reducing the cost of fertilizing the coconuts by 69%. In Bali, the three-strata forage system combines forage crops, shrub legumes and fodder trees, food crops (maize, soybean and cassava) and livestock. A study by Pretty and Hineb (2000) found that although the system reduced the yield of food crops because of reductions in the cropped area, forage yield was increased by 91% and composition of livestock feed benefited from a 13% increase in protein content. As a result, liveweight gains of steers increased and egg production and hatchability increased by 56% and 22% respectively. Soil erosion decreased by 57% while soil organic matter content increased by 11%. Fuelwood supply increased to meet 64% of annual needs. A project of a similar kind involving numerous farmers in India introduced trees, fodder and livestock in a previously homogeneous cropping system; the positive effects of diversification on soil and water retention turned an unproductive season into a productive one, resulting in a sharp decrease in seasonal out-migration (Pretty and Hineb, 2000).
