Application of the Law of Diminishing Returns to Some Fertilizer and Feed Data

In August, 1921, while studying the results of some fertilizer experiments at one of the experimental farms (Edgecombe Farm) of the North Carolina Department of Agriculture, it occurred to me that the successive increments in yield due to successive equal increments in fertilizer tend to form the terms of a decreasing geometric series. That is, if the increment in yield due to the second unit of fertilizer is, say, 70 per cent of that due to the first unit, then the increment due to the third unit tends to be 70 per cent of that due to the second, the increment due to the fourth unit tends to be 70 per cent of that due to the third, and so on until the quantity of fertilizer used becomes so large as to be injurious to the crop. Beyond this point the law would, of course, not hold, for the injurious effect of excessive fertilizer introduces a new factor.