60 PRINCIPLES OF FARM PRACTICE 



may be made which will answer the purposes of the crops 

 originally intended, and, at the same time, secure a much 

 larger production. For example, alfalfa may be desired, but 

 when soil conditions are examined, they may be found to be 

 unsuited to this crop. But these conditions may not be so 

 unfavorable for the production of red clover. Since red 

 clover has nearly the same uses and value as alfalfa, it may 

 be substituted with the probability of a much greater pro- 

 duction. Many disappointments in attempting to grow 

 alfalfa and other crops are doubtless due largely to a failure 

 to consider the soil needs of the crop in relation to the actual 

 soil conditions on the farm. 



How planning a cropping system affects choice of crops. 

 By " cropping system " is meant the operation, through a 

 period of several years, of a definite plan of crop production 

 for the entire farm. A number of things are involved in 

 making such a plan. The most important are the mainte- 

 nance of soil fertility; control of injuries and losses due to 

 weeds, insects, and plant diseases; the disposal of crops 

 (whether as feed for stock raised on the farm or as cash crops) ; 

 the competition with crops of better favored regions; and 

 distribution of labor. 



How to manage crops so as to maintain soil fertility. 

 Experience has shown that when one crop is grown con- 

 tinuously on the same field, there is a decrease in yield, often 

 to a point where there is no profit. There are several reasons 

 for this. The continual removal of organic matter destroys 

 good tilth, especially by reducing granulation and the water- 

 holding capacity of the soil; the removal of plant-food ma- 

 terials tends to exhaust the supply, particularly of nitrogen 

 and phosphorus; certain poisonous substances, called soil 

 toxins, accumulate and interfere with plant growth; the 



