The rotation of crops and the use of manure have frequently been shown to be important in maintaining soil fertility. Their value is again emphasized by the results of experiments conducted by the agronomy section of the Iowa Agricultural Experiment Station at Ames, on the Carrington loam, the principal soil type of the Wisconsin drift area.
These results show clearly that rotation is not only beneficial to the soil, but that it brings more profitable yields as well, if the rotation be suited to the particular soil. They show, too, that the use of manure increases crop yields, but also that it must be applied in the right amounts, at the right time and in the right way, for some methods of applying are better than others.
Stevenson, W. H. and Brown, P. E.
"Rotation and manure experiments on the Wisconsin drift soil area,"
Bulletin: Vol. 14
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletin/vol14/iss167/1