Competition for land between sectors and production systems is projected to intensify. It is expressed most accurately in the expansion of the use of land for arable and tree crops, shifting cultivation and grazing of livestock and its conservation under forest. Then there is the competition between crop and livestock production and, on a much smaller scale, between crop production or mangrove swamp preservation and aquaculture, there will be further pressures on the forest for timber and fuelwood extraction. Finally, increasing population and economic growth will contribute to further diversion of land to human settlements and infrastructure.
There is widespread evidence of erosion resulting in losses greatly in excess of 50 tonnes of soil per hectare per year, losses that may be five or more times the natural rate of soil formation.
Soil nutrient mining
The shortening of fallows and prolonged crop harvesting without adequate technological responses to replace the soil nutrients taken out by crops with organic or mineral fertilizer inputs, leguminous crops, nitrogen-fixing algae and so on is lowering the nutrient status of soils and the actual or potential crop yields. It consequently threatens the sustainability of agricultural production and also introduces an additional economic cost because the lack of balance lowers the technical efficiency of the mix of fertilizer nutrients.
Salinization of soils
This is primarily a problem of irrigated areas, but also occurs in hot dry zones where strong evaporation brings salts to the surface. In irrigated areas it is usually the consequence of bad design causing poor drainage, and/or inadequate maintenance and inefficient management leading to excessive application rates, and seepage from water courses. The end result is waterlogging, salinization, depressed crop yields and eventually, if corrective action is not taken, loss of land for agriculture. This leads to physical pressures on the finite resource base if land is permanently lost, which according to some estimates may vary in the range 0.2-1.5 million ha per year worldwide, while some 10 to 15 percent of irrigated land is to some extent degraded through waterlogging and salinization.
Oil nutrient mining and the overcultivation of fragile soils does lead to dryland degradation and desertification.
The principal threats of agricultural origin are the following: rising salt concentrations in irrigated areas; fertilizer and pesticide contamination of surface and groundwater; and discharges of organic effluents from intensive livestock units and fish farms.