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 agriculture, the fertilizer requirement is provided in the form of ash by felling and burning the forest

vegetation prior to cropping. When the land is abandoned after one to three years of cropping, soil

regains its original fertility characteristics through forest regeneration, provided the fallow period is

of sufficient duration. Nomadic Pastoralism Nomadic pastoralism is a subsistence agro-ecosystem

which usually prevails in semi-arid or arid regions which are too dry to sustain rain fed, field crop

ecosystems. Human densities associated with nomadic pastoralism are low, much lower than in

shifting agriculture. This is largely due to two reasons viz., (a) Low and Unpredictable Primary

Production Caused By Low And Highly Erratic Rainfall (B) Dependence on secondary production by

warm blooded herbivores. This result is only a small proportion of the energy fixed in primary

production being available to humans, who aresecondary consumers in this agro-ecosystem.

Pastoralism however allows conversion of low quality, inedible plant biomass viz., grass, to high

quality foods viz., meat and milk, in regions which would not support any people on the basis of crop

production. In range grazing, a high proportion of nutrients is recycled via plant residues since the

proportion of available herbage consumed by livestock or other herbivores is low. The nutrient cycle

is thus small in magnitude and highly dependent on release of nutrients by organic matter

decomposition. The rate of this process is impeded by the lack of soil moisture over a large part of

the year. The practice of burning speeds up nutrient turnover but it also increases losses of nitrogen.

All nutrients are also subject to loss by runoff due to heavy rainfall intensities during the short wet

season. Nitrification is also very slow. In nomadic pastoralism, manipulation of the environment is

usually limited to selection of grazing routes and watering sites. The environment is manipulated to

a greater extent where wells are provided to improve water supplies for cattle and where fires are

set off to improve the quality and quantity of natural grazing. Non-industrial and semi-industrial

continuous agriculture Eco-systems created by humans and characterized by continuous field crop

husbandry are often termed field crop ecosystems. They are cultivated plant communities which are

managed to achieve goals such as the production of food and other useful agricultural commodities;

financial gain; and personal satisfaction. Usually, they are managed to achieve a combination of

these goals. Field crop ecosystems fall into two main categories viz., non-industrial agriculture and

industrial agriculture. Those in the former category are largely self contained agro-ecosystems, while

those in the latter category are part of, and dependent upon, other elements within larger agro￾ecosystems. Field crop ecosystems differ from natural ecosystems in several plant andcommunity

characteristics as well as in their functioning.These differences are summarized below Field crop

ecosystems may be categorized as monocultural systems when they are dominated by a single crop

species and as multi-crop systems when no single crop species is dominant. There is a continuous

gradient from high input monocultural systems at one end of the spectrum to low input multi-crop

system at the other. Mixed farming systems, in which cropping and livestock subsystems are

integrated within a single agro-ecosystem, constitute a special category of multi- cropping systems,

in which one or more of the crops grown are grazed or used as fodder. Besides outputs in various

forms such as meat and milk, the livestock subsystem also provides the cropping subsystem with

(a)fertilizer in the form of manure and (b) a source of power for variousIndustrial agriculture is

primarily distinguished by the substitution of fossil fuel energy for human labour and a animal

power

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