CHAPTER XV 

 ROTATION OF CROPS 



142. Rotation. The amount of mineral food which a 

 crop will take from the soil varies with the kind of crop, 

 depending on how much of the crop is removed by the 

 yearly harvest, the richness of the land, and many 

 seasonal features which are too complex to be discussed 

 here. By referring to the table in the appendix it will 

 be seen that the amount of nitrogen removed by the 

 grain crops is less than the amount removed by crops 

 grown for their roots. It will be noticed, also, that grain 

 crops remove or require large amounts of phosphorus; 

 root crops, potash; and hay crops, much nitrogen; an 

 exception being made for legumes like alfalfa, clover, or 

 cow peas when grown as hay crops (^ 117). Some 

 legume crop should be included in any system of rota- 

 tion. 



143. Order of Succession in Rotation. It is desirable 

 to arrange the rotation so that the same land does not 

 have the same crop twice in succession. In arranging the 

 crop it is important to consider the order in which the 

 crops should follow each other. Plants with shallow roots 

 should follow plants with deep-feeding roots; non-cul- 

 tivated crops, like grain, should follow cultivated crops, 

 because the land will be in better tilth. As regards the 

 predominating mineral foods, it is better to let those 

 crops requiring large amounts of nitrogen follow potash- 

 loving crops, or, still better, legumes, because they 

 will leave additional amounts of nitrogen in the soil which 



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