Pressures arise from the increasing need to bring land into the crop production - fallow land cycle of agricultural production. This is itself related to the pressures resulting from increased human populations. This basically consists of the following steps:
Burning and grazing mainly transform and only slightly reduce the production potential. Soil fertility and regeneration capacity of the environment is still high. Along with changes in the composition of the vegetation the quality and availability of pastures gradually increase till the moment that land is taken in use for crop cultivation.
Reclaimed land sub marginal for crop cultivation
Long periods of permanent grazing result in a gradual mining of plant nutrients through animal products and manure deposed outside the area. Next, permanent grazing and repeated burning will result in a permanent composition of the vegetation different from the climax vegetation. In general wood is also is harvested from these pastures, reducing tree cover. These activities together with the formation of cattle tracks may result accelerated erosion, mainly depending on topography, soil characteristics, climatic conditions and intensity of exploitation.
Crop cultivation period
Soil fertility and structure decline rapidly as a result of repeated crop cultivation. The use of crop residues as feed will increase availability of plant nutrients for the next crop, but at the cost of nutrient loss in absolute terms (through leaching, volatilisation and export of animal products). Only manure from feed originating from outside the farm can compensate for exports through crop and animal products and for losses that occur during cultivation and the conversion of crop residues.
During the cultivation period the vegetation cover of the soil is poorest at times that risks for accelerated wind and water erosion are highest (particularly at the onset of the growing season). Prolonged cultivation periods may also result in fallow land that no longer has the potential to reach similar levels of production before the start of the next production cycle. The use of draught animal power can contribute to a prolonged periods of cultivation and shortening of fallow periods.
Feed quality of crop residues is poor. Feed seasonally available in limited quantities. The grazing of crop residues can result in transfer of plant nutrients from farms without livestock to those farms with livestock.
Whether the grazing of fallow vegetation will enhance or decrease the regeneration of the production potential of land depends mainly on the remaining soil fertility after cultivation and the grazing pressure on the fallow vegetation:
In earlier days people moved on when soil fertility of cropland had declined below productive levels. Regularly they took new land into production, leaving behind fallow land that progressively regenerated into forests and woodlands. This traditional pattern of shifting cultivation has resulted in secondary forests / woodlands and transitional vegetation in many of the semi-arid and sub-humid areas.
Due to population increase, sedentarisation and land scarcity, the normal pattern today is that farmers keep control over their fallow land and bring it into production again much earlier - usually well before the full regeneration of the basic production potential of the land.
Investments in rural areas as such as in irrigation facilities and flood prevention have reduced the area of permanent pastures available for livestock of both mixed farming and grazing systems (usually at the expense of increased cultivation). In addition some former communal grazing areas have been claimed for the conservation of wild life and biodiversity (both of which are severely threatened). Consequently the pressure resulting from mixed farming and grazing systems on remaining communal pastures and on the use of crop residues as feed resource is increasing.
Limited land is available for agricultural expansion. As a result pasture land that has marginal potential for crop production is increasingly utilised for crops. The degree of sedentarisation is also important. Decreasing mobility inevitably results in an increased concentration of land under cultivation - which itself results in shorter fallow periods. Expansion if irrigated land into former grazing areas and an increase in flood protection structures (construction of dams and dikes) further reduces the available communal grazing area. These resources were often seasonally important to livestock production (e.g. on flood plains).
Present trends in general result in
In response to less access to communal pastures and to an increasing competition on remaining pastures, individual farmers will start to harvest and conserve own crop residues for periods of feed scarcity. The system evolves in a mixed farming system characterised by managing its own crop residues. However lack of additional pasture / feed will limit the number of animals that can be kept in association with crop cultivation.
To prevent damage by livestock to crops and / or further degradation of communal pastures the community can introduce rules and regulations that limits free grazing in and near the cropping zone (grazing may be completely stopped). Systems can then evolve into cut and carry systems. Labour constraints will limit the number of animals that can be kept under this system.
Depending on the role and opportunities to gain an income from livestock, the farmer can decide to use part of his land to produce fodder crops. The system may then evolve in a mixed farming system characterised by feed production on farm.
A response based on the use of external feed in systems that are still based on the grazing of communal pastures is rare.
Response is therefore characterised by:
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