The availability of land and water resources is basic to all agricultural activity. Agriculture is often the major user of both of these resources, which can affect the flow of surface water and the loss of soil sediment from agricultural land. Appropriate land use, combined with environmentally sound soil and water management practices can help to reduce the peak flow of surface water and loss of soil sediment.
Damage caused by off-farm sediment flows is important in many OECD countries, but especially in regions where there are alternate periods of drought followed by heavy rainfall which limits soil vegetation cover. For countries with steep and rapid rivers and experiencing heavy rainfall, a high priority is placed on flood and landslide prevention, the consequences of which can be costly to the economy.
An important consideration for policy makers is to take into account the risks that are increased or mitigated by certain land use and management practices in agriculture. The measurement of such risks can contribute to better decision-making to promote or moderate changes in land use, and appropriate management practices. Two indicators are being developed by OECD to address land conservation issues, first, the water retaining capacity of agriculture, and second, the off-farm soil sediment flow from agriculture.
The water retaining capacity indicator measures the quantity of water that can be retained in the short term in agricultural soil, as well as on agricultural land, and by agricultural irrigation or drainage facilities. This indicator shows how much water a given area of land can hold taking into account differences in land use, soil types, management practices and other relevant factors. A decrease in water retaining capacity implies a greater potential risk of flooding.
The indicator of the water retaining capacity of agricultural land mainly reflects differences in land use, which vary in their capacity to retain water. There is at present a lack of information on soil types and management practices, which would help to improve the sensitivity of the indicator. On the basis of this more limited appraisal of agricultural water retaining capacity, however, most OECD countries have experienced a decrease, and only a few an increase, in water retaining capacity over the last decade.
The off-farm sediment flow indicator measures the quantity of soil erosion sediments delivered to off-farm areas as a result of agricultural soil erosion. The focus of this indicator is on the mitigation of soil erosion through land use and management practices, rather than just the measurement of soil erosion itself. It is not possible to show the trend of this indicator across OECD countries as the approach needs to be harmonised and data deficiencies overcome.
Some estimates, however, of the annual monetary cost of the damage to rivers, lakes and reservoirs incurred through soil sediment removal off-farm and damage to the recreational, transport and environmental functions associated with many water courses, suggest these costs are high. Evidence from related indicators on soil management and soil erosion would suggest that the rate of soil sediment flows from agricultural land to off-farm areas, especially water courses, might be decreasing for some countries.