442 



STATE BOARD OF AGRICULTURE. 



greater percentage of increase of crop tlian does a larger one. This 

 means, of course, tliat there is a limit to tlie profitable use of tlieni, in;is- 

 much as the cost of the fertilizer rises in direct proportion to the amount 

 used ; the rate of increase in the yield does not do so after a certain point 

 is reached and, finally the value of the product becomes less than the cost 

 of the fertilizer. Naturally those wlio cannot afford to take chances on 

 the weather, fluctuation in prices, and other conditions should be some- 

 what more conservative in their use than others. The law of diminishing 

 returns with respect to the use of fertilizers is illustrated in figure 4. 



AVhere rock pliosphate, the slow acting form, is utilized as a source 

 of phosphorus, the applications range in amount from 1000 to 2000 

 pounds. per acre, the slow availability being made up for in quantity. 



1 



V. 



1) 



a 



Q 



/Amount of rcrtil'izer Applied 



Figure 4. — ^The law of diminishing returns should be considered in using fertilizers. The 

 greatest returns on the investment may not be obtained from very large applications. 



It is generally agreed that this material is most effective when applied 

 to the soil along with barnyard manure, green manures, or crop residues. 

 If the soil is low in organic matter ^the larger applications are usually 

 advisable. 



Bone meal, being somewhat more active than the floats, is used in 

 smaller quantities. Wliere it is applied to the soil to increase the yield 

 of small grains and grasses, 300 to GOO pound applications per acre are 

 made and 1000 or more pounds for the larger cash crops. This form is 

 not extensively used in Michigan. 



The active form or acid phospliate is applied to the small grains and 

 grasses in amounts ranging from 80 to 300 pounds per acre, the average 

 being about 200 pounds; for potatoes, beets and tomatoes, 300 to 500 

 pounds are usually considered ample while somewhat larger amounts are 

 sometimes utilized for the production of cabbage, onions and celery. 

 It is generally considered to' be inadvisable to mix acid phosphate with 



