Part IL] MAINTENANCE OF SOIL FERTILITY. 41 



crops. In this experiment the kainit treatment has not been 

 repeated. 



These experiments have demonstrated the possibiUty of 

 increasing the effectiveness of raw rock phosphate by incor- 

 porating it with manure, but even after this has been done the 

 acid phosphate has usually been the more economical material 

 to use. Where we have used acid phosphate and raw phosphate 

 rock side by side, as direct applications to the land, the differ- 

 ence in outcome has more than covered the entire cost of the 

 acid phosphate. 



Fertilizing Truck Crops. 



Thus far I have discussed the question of fertility mainte- 

 nance from the standpoint of the farmer whose chief product is 

 the cereal grains, and this farmer represents the average Ohio 

 farmer. But even in Ohio there is a considerable and con- 

 stantly increasing class of farmers whose chief interest is the 

 production of the vegetables required by our rapidly growing 

 cities, which already contain more than half the total popula- 

 tion of the State, while in Massachusetts the production of the 

 cereals sinks into insignificance when compared with that of 

 vegetables and fruit. 



It is true that the great farm product of Massachusetts is 

 milk, no other single product equaling it in value, and the 

 production of milk probably exhausts the phosphorus supply 

 of the soil quite as rapidly as that of the cereal grains. 



The Massachusetts dairyman is a large purchaser of oil 

 meals and similar feeding stuffs, some of which, especially the 

 wheat offals, carry a considerable percentage of phgsphorus. 

 It would require, however, a daily ration of 6 or 7 pounds of 

 wheat bran or cottonseed meal to carry into a ton of manure as 

 much phosphorus as has been added in 40 pounds of acid 

 phosphate. Moreover, the manure used in these experiments 

 has been produced by fattening cattle, fed a ration high in this 

 element. 



Phosphorus, however, is not the only important element 

 in which the soil may be depleted through an uninformed 

 system of agriculture. The Ohio Experiment Station has been 

 conducting a series of experiments in the feeding of milch 



