THE ROTATION OF CROPS 171 



manure and corn is extensively and advantageously used as feed for live- 

 stock, corn may be grown two years in succession, especially when the 

 soil is fertile and manure is available for both the first and second crops. 

 It is desirable that crops be arranged in such a way that the improving 

 effects of each crop shall be regularly received and the ill effects of the 

 exhaustive crops be systematically neutralized by the crop that follows. 



Length of Rotations. — The length of crop rotations will be deter- 

 mined by local conditions and the character of crops grown, together 

 with the value of land and cost of labor. Crops that are costly to estab- 

 lish, such as alfalfa, should occupy the land for two or more years in order 

 to minimize the annual cost of production. The length of time that a 

 crop remains productive is also a factor. The annual cost of seed and 

 the preparation of the land for the crop is one-half or one-third as much 

 if the crop is continued for two or three years respectively, as it is if 

 allowed to remain only one year. So long as the yield is satisfactory, 

 it generally pays to continue the crop. This tends toward a longer crop 

 rotation. 



In many localities where general farm crops prevail, a seven-year 

 rotation is common, such for example as corn, oats, wheat and mixed 

 clover and timothy for four years. Such long rotations with only one 

 legume in them do not make for increased soil fertility, unless all the 

 crops produced are fed upon the farm and the manure returned to the 

 fields. Where cash crops dominate the type of farming, short rotations 

 may be better. A rotation of corn, wheat and clover or of potatoes, 

 wheat and clover affords the maximum of cash crops, while the frequency 

 of clover in the rotation tends to maintain the nitrogen supply of the soil. 

 Such short rotations also maintain the soil in good tilth as a result of the 

 frequent plowing and abundant tillage. 



What Crops to Grow. — The crops to be grown in a rotation will be 

 determined by a number of factors, as soil adaptation, length of growing 

 season, market demands, transportation facilities, and the system of 

 farming that prevails. Aside from these facts there is another considera- 

 tion that must not be overlooked. Usually it is unwise to follow a crop 

 like tobacco, which is considered a gross feeder, with another crop such 

 as corn having similar feeding habits. Such a practice is permissible 

 only on very fertile soil or where the quality of the following crops is to be 

 influenced through reduction in organic matter or available plant food. 

 For example, coarseness in tobacco might be reduced by having it pre- 

 ceded by corn. 



When to Apply Manure and Fertilizers. — It is generally advisable 

 to apply barnyard manure to those crops in the rotation that have a long 

 growing season or a high money value, or to those that are considered 

 gross feeders, such as corn. In the absence of manure, the same rule 

 will apply in the applications of commercial fertilizers. When manure is 

 supplemented with fertilizers, the fertilizers are best adapted to crops of 



