A number of human activities so reduce the fertility of land, or degrade the soil, that large tracts of land must eventually be abandoned as being totally unproductive. This is the case in several agricultural methods. The failure to use the various forms of agricultural rotation - grass to crop to fallow, for instance - which were previously employed to remedy the 'soil fatigue' which uninterrupted growth of one crop often brings, has resulted in a decline in the organic humus content of the soil. Loss of fertility is usually quite irreversible, though there are examples where the process of intensive land-use, abandonment, and regeneration, have been incorporated into agricultural practices, as in the cyclical movements of 'slash-and-burn' forest tribes and of nomadic herdsmen on brush-land.
In many developing countries a heavy pressure of population, leading to increased demand for food, has been a major factor behind the cultivation of marginal lands, such as hill-sides and river banks, which directly leads to soil erosion. The increased irrigation needed for food production may also lead to problems such as salinization. Agricultural and animal husbandry practices, such as the shortening of the fallow period under shifting cultivation due to demographic pressure, and overgrazing, have often contributed to soil degradation. Rising costs of alternative energy as well as poverty and increase in population have led to increased demand for fuelwood and hence to accelerated deforestation. Crops that have high economic yield or commercial profitability (such as, in recent years, maize and soyabeans) have also been found on occasion to aid soil degradation.