À Friedrich Engels, le 3 janvier 1868

I would like to know from Schorlemmer what is the latest and best book (German) on agricultural chemistry. Furthermore, what is the present state of argument between the mineral-fertiliser people and the nitrogen-fertiliser people ? (Since I last looked into the subject, all sorts of new things have appeared in Germany.) Does he know anything about the most recent Germans who have written against Liebig’s soil-exhaustion theory ? Does he know about the alluvion theory of Munich agronomist Fraas (Professor at Munich University) ?