Ten years of experiments at Ames on the principal Iowa type of the Wisconsin drift soil point clearly to the fact that the farming systems of this large soil area must be modified if the land is to be kept permanently fertile.
These modified systems of farming, as the results of the Ames test show, must be based on a definite rotation of crops, including some legume which is turned under as a green manure or fed to livestock on the farm. It must make provision for the careful saving of all manure produced on the farm and its most effective use, for it is the cheapest and best fertilizer. With grain farming, the need of a legume in the rotation to be turned under is especially urgent to keep up the soil’s nitrogen content. Some time in the future .the use of phosphorus and potassium fertilizers must be considered, though at present they do not seem necessary on the particular soils tested. Drainage is all important and is a first requisite to satisfactory yields on the Wisconsin drift area. Thorough cultivation is likewise essential and there is need of testing for acidity and the application of lime where the soils are sour.
Stevenson, W. H.; Brown, P. E.; and Forman, L. W.
"Maintaining fertility in the Wisconsin drift soil area of Iowa,"
Bulletin: Vol. 14
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletin/vol14/iss161/1