302 SOILS 



A third advantage of rotating crops, in its rela- 

 tion to soil fertility, is the opportunity provided for 

 improving the texture of the soil. When crops are 

 harvested the roots and stubble are plowed under, 

 and since crops vary in the amount of herbage 

 returned, and the depth and extent of the root 

 system, there is greater likelihood that all parts 

 will be benefited by the humus resulting from the 

 decay of roots if several crops are grown. Further- 

 more, a rotation permits the use of cover crops, 

 catch crops, and other means of improving texture, 

 as discussed in Chapter XII. 



Rotation of Crops and Weediness. Certain weeds 

 go with a certain crop ; they seem to find a niche in 

 its cultivation that just fits their needs. Thus 

 we have quack grass in the asparagus bed, purslane 

 in the onions and Canada thistles in the wheat. 

 Furthermore, some crops can be kept free from 

 weeds much easier than others. Note how much 

 faster weeds multiply when sown crops are grown, 

 as rye, oats or wheat, than when crops that are 

 inter- tilled are grown, as corn and potatoes. In 

 this country, weeds cause the greatest loss in the 

 grain fields of the West, where continuous cropping, 

 with or without summer fallow, is practised. 

 Wherever the single-crop system is dominant, weeds 

 become a serious nuisance. 



A specific instance where a rotation of crops 

 may be used for cleaning land of weeds will call 

 attention to the usefulness of the practice. Wild 

 carrot and plantain are very troublesome weeds 

 in some localities, especially in the Northeastern 

 States. These plants do not produce seeds until 

 mid-summer. If a two-year rotation of wheat or 

 rye and clover is practised these weeds may be 

 almost completely exterminated, for as soon as 



