The effect of different fertilizer treatments on the nitrogen and organic matter content of a soil when cropped to a definite rotation for a period of twenty-four years

In a large part of the soil fertility studies that have been attempted in the past, a great number of the results obtained were based almost entirely on crop yields. These yields were used as the final criterion upon which to draw conclusions as to whether a given system of soil management was a profitable one. At the Virginia Agricultural Experiment Station, Blacksburg, Virginia, a series of rotation and continuous cropping experiments have been undergoing a specified treatment for a period of 24 years. Conclusions as to the expediency of the practices followed have been approached from a purely crop yield basis. This method is serving its purpose in showing exactly how much the land is producing at the present time under a given soil management practice.

It is believed, however, that a soil management program goes further than this. A practice based on crop production alone may prove, over a long period of time, to be a poor one. Perhaps just as important are the conditions arising within the soil relating to these practices. Whether or not the system evolved is one of soil building rather than one of soil depletion, is a question which necessarily must be considered before any recommendation as to the soil management practices to be followed, may be attempted.