Economic costs of soil erosion
The following questions can be asked related to the economic effects of soil erosion:
1. How high is the decrease in crop yield per cm loss of topsoil depth? Does, in fact, soil productivity decrease much further, once the original humus rich A1-horizon of the natural soil profile is gone, such as is the case in large parts of Europe with its centuries old cultural landscapes (provided that sufficient rooting depth remains)?
2. What is the extent of the offsite damage caused by soil erosion around the world? How widespread is it?
3. How high are the economic costs of soil erosion around the world today? Is there a trend in economic costs visible over the past hundred years?
4. How much does it cost farmers to apply soil erosion control measures on their farms?
5. On how many acres of cultivated land around the world soil erosion control measures are practiced today, and has this led to a reduction of the onsite and offsite effects and related economic costs of soil erosion?
Quantitative data to answer these questions are scarce.
A preliminary question is: How
well do we really know the rate of soil erosion? On the measurement of
soil erosion Lal
Fourteen years later Garcia-Ruiz et al. (2015) in their paper "A meta-analysis of soil erosion rates across the world" still warn that the data obtained have not been independent of the method used.
Contrary views on the importance
of soil erosion have been expressed by Pimentel (1995, 2006, 2013) and
Crosson (1995, 2000).
Soil erosion in the United States has been a matter of public concern since the 1930s. Conditions were improved by the 1960s, although no one knew just how much. Starting in the 1970s, however, several studies concluded that erosion was high. Although a few studies have been skeptical of these high rates, most have suggested that soil erosion is an extremely serious environmental problem, if not a crisis. Quantification of the problem has been elusive, and average annual U.S. cropland soil erosion losses have been given as 2 billion, 4.0 billion, 4.5 billion, 4.8 billion, 5 billion, or 6.8 billion tons.
The remarkable feature of all this discussion and attempted rectification is that it was based mostly on models. Little physical, field-based evidence (other than anecdotal statements) has been offered to verify the high estimates. It is questionable whether there has ever been another perceived public problem for which so much time, effort, and money were spent in light of so little scientific evidence.
Pimentel and Burgess
Since humans worldwide obtain more than 99.7% of their food (calories) from the land and less than 0.3% from the oceans and aquatic ecosystems, preserving cropland and maintaining soil fertility should be of the highest importance to human welfare. Soil erosion is one of the most serious threats facing world food production. Each year about 10 million ha of cropland are lost due to soil erosion, thus reducing the cropland available for world food production. The loss of cropland is a serious problem because the World Health Organization and the Food and Agricultural Organization report that two-thirds of the world population is malnourished. Overall, soil is being lost from agricultural areas 10 to 40 times faster than the rate of soil formation imperiling humanity’s food security.
Regarding the first of the five
questions above Bakker
(2005) write as follows:
Although the problem has received much attention recently, hardly any quantitative information on the effect of erosion on agricultural productivity exists. The quantitative information derived at the plot scale is scattered and incoherent, and no quantitative information at the regional or national level (i.e. the level relevant for food production) exists. Inferences made from the synchronicity of soil erosion events and societal changes are therefore not based on quantitative assessments of the impact of soil erosion on agricultural productivity, nor are analogies between the collapse of an-cient societies and the risks facing modern society. For this reason, the extent to which soil erosion is indeed a significant threat to the agricultural productivity of modern societies is an important subject for debate.
The research presented here reports of
statistical analysis of both
plot and regional scale with respect to the erosion-productivity
relationship. A meta-analysis of plot scale experiments shows that the
different methodologies used for the erosion-productivity assessments
bear part of the responsibility for the incoherence of the outcomes.At
the plot scale, the effect of soil
erosion on crop growth has been assessed in numerous experiments where
erosion was either simulated by artificial desurfacing, or where
productivity losses in strongly eroded areas were compared with losses
from less eroded areas. A systematic overestimation of the effects may
apply to the first category of experiments, which make up a large part
of the research results. Correcting for this overestimation reveals
that under intensive,
mechanized agriculture yield reductions at the
field scale are of the order of only 4% for each 0.1 m of soil loss.
Given the fact that the removal of 0.1 m of soil required either long
time-spans, or very high erosion rates, this number makes it highly
unlikely that erosion may pose a serious threat to food production in
modern societies within the coming centuries. An empirical
the relationship between erosion and productivity for modern
agriculture at the regional scale, also shows no agreement with
previous assumptions concerning the importance of the impact of erosion
on agricultural productivity either. The results of this analysis
converge with the corrected plot-scale findings of approx-imately 4%
per 0.1 m of soil loss. (underscored
The most comprehensive study of the impact of soil erosion on crop productivity is Den Biggelaar et al. (Parts 1 and 2, 2004).
They start by remarking:
Despite millions of dollars invested in erosion research, it is difficult to state precisely what effect the loss of a unit of soil has on crop yield (Lal, 1987a). This is due in part, as Perrens and Trustum (1984) and Erenstein (1999) observed, to the fact that there is no direct, clear-cut relationship between erosion and productivity, making the assessment of the impact of erosion on productivity difficult. Productivity decline may not relate directly to the amount of soil loss (expressed in Mg or cm ha 21 yr 21 ), but may be a result of erosion-induced changes in the physical, chemical, and biological qualities of soil that influence production (e.g., water holding capacity, soil organic matter (SOM) and nutrient contents, and bulk density). Moreover, soil is only one of the factors affecting productivity, as crop yield is a function of many variables.
of the conclusions of
Part 1 (p. 36) is:
The results of the present analysis show that average crop yields and effects of past erosion on yields (measured in Mg yield decline per cm of erosion) differ greatly by crop, continent and soil order. However, aggregated across soils on the continental level, differences in productivity declines per Mg of soil erosion are fairly small. The absolute yield loss ranged between -0.49 and 1.44 kg/ha/Mg of soil erosion for grain and leguminous crops, and 0.69 and 127.0 kg/ha/Mg for root crops. However, due to differences in mean yields, the relative yield losses per Mg of soil erosion vary more, even though losses were generally small (<< 0.1%/Mg of soil erosion). The exceptions to this general rule were studies on potatoes in North America, in which yields declined by 0.42%/Mg.
In Part 2 (pp. 91-92) Den Biggelaar et
Three main conclusions can be drawn from our analyses:
First, estimated annual losses at a global scale for the crops and continents considered in our analyses are small relative to the total agricultural production and value of the selected crops. The losses are likely to be masked over the short term by market fluctuations, weather, and other environmental perturbations, diminishing incentives for farmers to adopt conservation practices. Moreover, erosion’s impacts are cumulative and may cause more serious losses if it continues unabated over a long period of time.
Second, our estimated global annual losses in crop yields and production are at the lower end of the range of previously published estimates of erosion-induced productivity losses (Lal and Stewart. 1990; Janargin and Smith, 1993; Crosson, 1997; Lal, 1998;Young, 1999). Of more interest, especially for soil conservation policy is the finding that losses vary widely between crops, soil orders and regions, and in selected situations can be quite substantial. In general, though, little is known about these losses for many important crops in many developing countries.
Third, estimated losses in productivity are probably small in relation to offsite impacts (such as sedimentation). These findings underscore the importance of continued policy measures to encourage soil conservation. They also underscore the importance of improved understanding of erosion and its impacts for these crops, soils, and regions where its impacts are most severe or least understood. Finally, more precise estimation of actual losses due to erosion (as opposed to the potential losses estimated here) depends on improved understanding of farmers’ optimal response in the face of changing physical, market, and policy environments.
on the available data, it is very difficult to assess how much soil
erosion is costing society in England and Wales. We believe the absence
of such analysis severely limits the ability to develop appropriately
funded policy options to deal with soil erosion effectively. This
position is succinctly stated in a June 2003 report of an OECD expert
meeting on agricultural soil erosion and soil biodiversity indicators: ‘Off-site
should be noted that there is considerable ambiguity in quantification
of off-site costs, and especially in how to quantify the impact of
agriculture on soil and other natural resources (air and water). This
ambiguity needs to be addressed. It was also noted that our capacity to
model and characterise off-site impacts remains rudimentary.’
Inman (2006, p. 16) on the economics of soil erosion in England and Wales:
The costs borne by society as a consequence of soil erosion are known as externalities by economists because they are costs which are not taken into account either by producers or consumers of agricultural goods and services. When such externalities are not included in prices, they distort the market by encouraging activities that are costly to society even if individual (private) benefits are large.
In the agricultural sector, externalities are regarded as having five characteristics or features: 1) their costs are often neglected; 2) they often occur with a time lag; 3) they often damage groups whose interests are not represented; 4) the identity of the producer of the externality is not always known and; 5) they result in sub-optimal economic and policy solutions. Whilst it is relatively straight forward to identify generic externality categories, quantifying many of these categories in monetary terms is extremely difficult. Firstly, it is necessary to know the value of nature’s goods and services, and what happens to these when they are impacted. Secondly, many externalities are associated with non-market goods. For example, how do we value soil-water chemical interactions which produce clean water.
The following Table (from Telles, 2011, p. 293) gives estimates of soil erosion costs in dollars per year. The onsite costs were estimated on the basis of the loss of soil, nutrients, organic matter, productivity and yield. Offsite costs were estimated in various ways. However, the main offsite effects are linked to sedimentation. Depending on the methods used to estimate on- and offsite soil erosion costs, the results can be extremely variable. The majority of studies estimate onsite costs, and these studies show an even wider fluctuation in the estimated figures. Moreover, in terms of the breakdown of total erosion costs, offsite costs are higher than onsite costs.
erosion costs in dollars/year, data assembled from literature by Telles, 2011.