Enhancing soil quality is essential for maintaining agricultural productivity. It can be degraded through three processes: (i) physical (e.g. erosion, compaction); (ii) chemical (e.g. acidification, salinisation); and (iii) biological degradation (e.g. declines in organic matter). These degradation processes are linked to changes in farm management practices, climate and technology. There can be lags between the incidence of degradation, the initial recognition of a problem by farmers and the development of conservation strategies.
Some aspects of soil degradation are only slowly reversible (e.g. declines in organic matter) or are irreversible (e.g. erosion). Essentially farmers need to balance three key aspects of soil quality: sustaining soil fertility, conserving environmental quality, and protecting plant, animal and human health. Given the perspective of maintaining soil quality to ensure agricultural productivity, expenditure on soil conservation, both from private and government sources, is frequently a substantial share of total agri-environmental expenditure. Government policies dealing with soil quality improvement commonly provide a range of approaches, including investment and loans to promote conservation practices, and advice on soil management.
Indicators and recent trends
There are two OECD indicators that address on-farm soil quality: (i) risk of water erosion and (ii) risk of wind erosion. These are estimates of the share of agricultural land affected at different risk intervals from low/tolerable to high/severe categories. Water and wind erosion indicators are considered to be of highest priority, as other soil degradation processes, such as soil compaction and salinisation are, in general, only of concern in specific regions of OECD countries. Wind erosion is more prevalent in farming regions with major expanses of cultivated open prairies and rangeland.
While the area of agricultural land at high/severe risk to water and wind erosion is not extensive, for certain OECD countries more than 10 per cent of agricultural land fall within this risk class. Trends in water erosion over the past ten years, for a limited number of OECD countries appear to show a reduction from high/moderate classes into tolerable/low classes of water erosion. The reduction in both water and wind erosion largely reflects a combination of the adoption of conservation or no tillage, less intensive crop production and the removal of marginal land from production.
While, in some OECD countries, certain regions are affected to a significant extent by other forms of soil degradation, such as acidification, salinisation, soil compaction and toxic contamination, there is evidence that these problems are beginning to improve in some cases. These improvements are being achieved as a result of government schemes that provide encouragement and advice to farmers to adopt soil conservation practices, such as crop residue management, conservation and land retirement.
There are few estimates of the value of agricultural production foregone as a result of soil degradation, but those available indicate that it might be in excess of 5 per cent of the total annual value of agricultural production in some countries.