Sustainable systems are those that have existed for a considerable time. However, it must be recognized that no system can exist forever, i.e. any system becomes unsustainable sooner or later. All systems have to adjust continuously, particularly when the relationship between the system and its resource base becomes seriously out of balance. An example of a system and its resource base is the case of the infield/outfield ratio in EXPAGR or HEIA, or the ratio between management requirement and management capacity when a farming system shifts from HEIA into NCA. The following cases are illustrative of previously sustainable systems. They give clues for future development and for the choices in policy setting or research/extension priorities.
A mixed system that uses animals to graze "outfields" distant from the village in order to concentrate all or part of the excreted plant nutrients on the "infields" near the farmhouse is called an outfield/infield system. It is a form of mixing in the EXPAGR mode where land is abundant. The system exists (and has existed) in many forms. It can employ animals that are only stocked on crop fields at night while being grazed during the daytime, it can be intensified by constructing special stables in which straw from the crop land, litter from the forest or even topsoil from the outfield are used to conserve the nutrients of the dung and urine from the animals. As recycling on the farm increases, the system slowly moves into the LEIA or NCA mode. The system has existed throughout the world for many centuries, in pre-medieval Europe and in Russia until the early twentieth century, and it is still found today in many countries in the tropics. Improvements include the better conservation of nutrients in the stable, the better application of dung on the field (more timely and better localized), or the introduction of legumes for nitrogen supply. Examples have been given in Chapter 6, sections Nutrient losses and their prevention and Leys and catch crops, and in Photos 12, 58 and 90.
The Kano close-settled zone in the Soedano-Sahelian region of Nigeria has been the site of an intensive mixed farming system of the NCA mode where for the last 30 years all available land has been under annual cultivation. Small ruminants consume crop residues, in particular those of groundnuts and cowpeas, which are good quality fodder. The nitrogen in the residues of leguminous crops is conserved in the manure, which is transported with compound waste back to farmers' fields for use as fertilizer. Legume grains are sold, earning cash, which farmers may use to purchase inorganic fertilizer if they wish or other goods. Nutrients are added to the system when harmattan dust (a wind from the north carrying sand from the Sahara and North-Sahel) is deposited on farmers' fields during the dry season. The system allows farmers to manage an efficient nutrient recycling system centred on small ruminants and based on high labour inputs by farmers. They must keep animals tethered within the compound during the rainy season, collect crop residues and weeds for fodder, and transport the manure back to the fields.
Several elements have been important in the development of this farming system:
In addition, the farmers engage in crop, livestock and tree production to diversify their income. Many also practise non-farming economic activities, especially during the long dry season. This diversity allows them to cope with risks, whether environmental (e.g. drought) or economic (e.g. price fluctuations). The dependency on external inputs is low, permitting farmers to be independent of the fluctuations in the economy. Farmers use little inorganic fertilizer, and they maintain seed lines of favoured indigenous cultivars, rather than using the seed of commercially supplied high-yielding varieties. Hence, despite being one of the most densely populated areas in semi-arid West Africa, the system is both productive and sustainable - an example of farming in the NCA mode. The increasing population densities and labour availability are for the time being essential for a process of agricultural intensification, such as the increasing use of crop residues to feed livestock, and the use of farmyard manure on the fields.
A widely quoted example of population pressure and its impact on development and environment is that of the Machakos district in Kenya, another case of a shift to NCA. The key to the success of this system lies in the variety of livestock feeding methods. In the past, possibilities to integrate crops and livestock were neglected and the contribution of livestock to the household income was limited. One way of improvement was to establish individual titles to land, visualized in demarcation and enclosure of grazing areas. Subsequently, some farmers developed the grazing areas to provide grazing, timber and fuel. They used multipurpose animals, they did not aim at fast maturity, they even accepted seasonal weight losses of their livestock (a typical approach within LEIA and NCA), but they aimed at high production on an area basis (an illustration of the concept of communal ideotype). High stocking rates could be maintained through the use of crop residues, i.e. increasing population led to a reduced area of grazing land, a change in the role of cattle, and the replacement of livestock by specialized crops as the main source of cash. Adjustment was the key to sustainability, and population growth itself spontaneously responded to changed economic conditions between 1979 and 1989. Extreme shortages of land in parts of the district, combined with a national economic recession, high costs of education and other expenses for raising children, led to voluntary family planning. Finally, a programme in which people that had migrated to the city sent money back to the villages supported the process.
The evolution of the Machakos system differed between the drier and wetter areas of the district, and it depended on farm size:
In general, as land is scarce, fodder production was combined with soil conservation and stall feeding or tethering (Photo 102). Other methods of range improvement such as hedging, fencing, bush and indigenous tree management and scratch ploughing (superficial ploughing of the land), became attractive because they needed labour but almost no cash (a case of farming in LEIA mode).
A bird's-eye view of land conservation in Machakos (Kenya)
Increased population led, via higher food demand, more labour, increased knowledge, and a reduction in the per capita cost of physical and social infrastructure, to an autonomous development towards higher agricultural production. The means and incentives to invest money and work in farm improvement and the knowledge of new and appropriate technologies were instrumental in this change. The new technologies came from various sources, such as traders, merchants, research and extension, religious groups, educated relatives and experimenting fellow-farmers. Literacy and general knowledge were increasingly useful to find non-agricultural work, to make the most of a farming enterprise, and to participate in the various social and commercial networks. The development was assisted by government interventions and policies with respect to pricing, investments and education. Government also provided community development services and changed research and extension from a top-down approach to one involving farmers in the development of technology. It supported small towns in creating jobs and infrastructure and becoming centres of trade and services for the rural area. The Machakos case illustrates that farmers must be offered a variety of techniques from which they can select for managing pasture and other systems of animal feeding. The differentiation is necessary not only because agroclimatic conditions vary, but also because different combinations of grazing and stall-feeding may be economic for both small and large farmers.
This very intensive mode of integrated crop livestock farming originated in Flanders (Belgium) during the thirteenth and fourteenth centuries; it was elaborated in the United Kingdom in the seventeenth century. The system originates from conditions where the outfield/ infield ratio declined due to increased population pressure. Land became scarce relative to the population and EXPAGR was replaced by NCA. Grazing of animals on the outfield to manure the infield became impossible and farmers were forced to find other ways of providing nutrients to their crops. They did so by keeping animals in a system of zero grazing on deep litter, quite similar to the Kano case. The animals were fed on crop residues and on crops that could fix or mobilize nutrients such as nitrogen and phosphorus. Legumes fixed atmospheric nitrogen and rape crops (cruciferae) were used to mobilize soil phosphorus (Figure 2 and Photos 87 and 90). The proximity of the city helped to generate cash from the sale of animal produce. Moreover, the use of night soil from the city on the crop fields was one additional way to maintain soil fertility by further recycling, i.e. integration and mixed farming at regional level.
The effective use of legumes for nitrogen fixation in tropical areas is limited. The organic matter and associated protein quickly decomposes in conditions of high humidity and temperature, resulting in leaching and volatilization of nitrogen compounds before the crop can use this valuable nutrient. Eventually this can even lead to acidification of the soils, an example of apparently sustainable systems that eventually outdo themselves. However, the Mediterranean climate has a peculiar characteristic that distinguishes it from hot and humid tropical ones. The Mediterranean climate is characterized by wet, cool winters and hot but dry summers; it occurs in the United States and southern Australia, as well as around the Mediterranean. Under these conditions there is hardly any release of nitrogen in summer (soil microbes are inactive due to lack of water), and slow release of nitrogen in winter (water is available but temperatures are relative low). In southern Australia this resulted in a sustainable crop rotation of grains and legumes, where animals feed on the biomass of legumes, straw and failed crops.
The use of a mustard/berseem (cruciferae/legume) mixture for animal feed in the Gangetic plains of India to maintain nitrogen, phosphorus and soil organic matter
A specific crop-livestock system based on a contribution of sugar cane/pigs and biogas has been developed in Colombia. It is called the CIPAV system, after the name of the institute where it was developed. It is being applied and tested in several parts of the world and the main ingredient is sugar cane, which produces the feed (juice and tops) and fuel (bagasse). Multipurpose trees and water plants such as duckweed supply the protein, while the trees also play other important roles such as controlling erosion, providing sinks for carbon dioxide and methane and as a source of biodiversity. Sugar cane and trees have well-developed systems of biological pest control; they can also do without much synthetic chemical input. Also they are easily separated into high and low-fibre fractions as required for the different end uses of feed for pigs, cattle and sheep and fuel. The preferred animal species are pigs and ducks, which adapt readily to the high-moisture feed resources (cane juice, tree leaves and water plants), and they have a high- meat:methane production ratio. Sheep, which can derive most of their feed from the cane tops and tree foliage, complement them. Buffaloes and/or triple purpose cattle can supply draught power as well as meat and milk. All the livestock are managed in partial or total confinement to minimize environmental damage and to maximize nutrient recycling to the crops. The CIPAV model is flexible, as witnessed by the increasing acceptance of many of the elements by resource-poor and entrepreneurial farmers.
This chapter has discussed cases of mixed crop-livestock systems that have proven to be sustainable for shorter or longer periods of time, across the world. More systems could have been elaborated, e.g. the integrated fish/pig/vegetable systems from China (BOSTID, 1981); cattle grazing under coconuts; the multilayer system developed on Bali (Nitis, 1995); the alley farming systems (Kang, Wilson and Lawson, 1984); the traditional paddy/livestock systems of Southeast Asia, etc. The point is, however, that a variety of mixed systems can be instrumental to sustainability. Still they may have to change their mode of farming with the ratio between population pressure and resource supply, which requires change in the community organization as well as attention to the whole rather than maximum yield of individual crop components. Sustainability therefore combines an element of change and attention to relationships between systems. Particularly the latter aspect tends to be forgotten in specialized farming of the HEIA mode which, therefore, may now have to re-integrate lessons and methods that it can learn from mixed farming.
6 Based on Harris (1996).
7 Based on Slingerland (2000), Tiffen, Mortimer and Ackello-Ogutu (1993) and Tiffen, Mortimer and Gichuki (1994a and b).
8 Based on FAO (1992c).