The data assembled by Lindert indicates that it has not come to any considerable extent from farm land. I find it hard to believe that farmers are as careless with a resource that is very important to them as is implied by much of the opinion expressed concerning the alleged enormous loss of topsoil. It is not in the interest of farmers to prevent all erosion since there are likely to be costs involved. But in the range where the benefits and costs of preventing erosion are approximately equal or the benefits exceed the costs, it seems reasonable to assume that farmers are acting in their own interest, at least until there is solid evidence to the contrary. Lindert's analysis of historical data for two important countries indicate that there may not be evidence to the contrary.
Soil surveys do exist in other countries.
It is perhaps time that more use is made of this neglected source of information about the state of the world's land resource and less reliance is placed on information that lacks a time dimension. Here are Johnson's references to Lindert. The number of hits on this page since 1999 August 27.