THE MAINTENANCE OF SOIL FERTILITY 559 



waste in its production and handling, the organic matter is 

 almost maintained and the loss of nitrogen is met to some ex- 

 tent. Under such a system, the addition of nitrogen and of 

 mineral constituents is a problem, although some attention 

 should be paid to the soil organic matter. Liming will be 

 necessary ultimately if not immediately, while the addition 

 of phosphoric acid obviously will some day be profitable. 

 If acid phosphate is utilized at a normal rate, the sulfur 

 losses that occur should be very nearly counterbalanced. 

 Potash, especially as the soil under consideration is a clay 

 loam, will no doubt be available for a long period if the 

 organic matter is adequately maintained. 



The use of a green-manure once in the rotation in addition 

 to the farm manure will adequately care for the soil or- 

 ganic matter and reduce the nitrogen problem to a minor 

 position. 



When animal products are relatively high in price and 

 crop values are low, stock farming will be advisable and a sys- 

 tem whereby considerable farm manure will be available may 

 be followed. It has already been indicated that under such 

 conditions the organic matter, and to a lesser degree the nitro- 

 gen content of the soil, may adequately be maintained espe- 

 cially if a green-manure is used once in the rotation. Where 

 grain farming is necessary, reliance must be placed almost 

 wholly on green-manures for the upkeep of the soil organic 

 matter, especial care being given to the full utilization of crop 

 residues. According to the data presented in Table CXXXI, 

 such a system, as far as the nitrogen and organic matter are 

 concerned, could be made about as satisfactory as where farm 

 manure is available and has the possibility and advantage of 

 considerable expansion. Grain farming makes necessary, 

 however, a more intensive and careful use of mineral constitu- 

 ents. Liming and commercial fertilizers will, therefore, fig- 

 ure somewhat more prominently in grain-growing than where 

 dairying or stock-raising are practiced. 



