THE PROPERTIES OF SOILS 63 



abundant supply of available plant food. A soil with a bluish 

 shade indicates poor ventilation, usually due to poor drainage. 

 This bluish color is due to the fact that the iron compounds are 

 not well oxidized because of lack of air. When such soils are 

 aerated by thorough drainage, the color changes to a dark brown 

 or red, depending upon the amount of organic matter and iron 

 present. Usually red or brown soils give up their plant food 

 readily to crops. They are therefore known as generous, or re- 

 sponsive, soils. Such soils are usually well adapted to clover, 

 wheat, and fruits. For the most part, the red soils of the 

 country are limestone soils, containing considerable iron, which 

 has been oxidized to iron rust through good drainage and aera- 

 tion. The organic matter is readily depleted in these soils by 

 cultivation, and they are likely to need organic matter and phos- 

 phates. Brown soils contain more organic matter and are usually 

 somewhat more fertile than red soils. The so-called chocolate 

 loams are famous for their agricultural value. Soils of a gray 

 color are among the lowest in productivity. 



67. Plant growth as an indication of soil fertility. One of 

 the best indications of a soil's fertility and value is the character 

 of the growth upon it. Rank, dark-green plants usually indicate 

 an abundance of organic matter and available nitrogen. Vege- 

 tation of a pale-green color, lacking in luxuriance of growth, 

 generally indicates a lack of organic matter and available nitro- 

 gen. Timber growth of softwood species, as basswood, walnut, 

 and papaw, indicates a fertile soil, well adapted to grain crops 

 and clovers. Large white oaks, hickory, and hard maple indicate 

 soil of medium fertility. Beech usually indicates poor land, as 

 do pines and most other cone-bearing trees. Swamp or water 

 oaks and red maple indicate poor drainage. An abundance of 

 legumes indicates a soil which contains plenty of lime, and is 

 well drained. The absence of legumes and the presence of 

 sorrel, dock, and horsetail indicate lack of lime and poor 

 drainage. The presence of shrubs like the huckleberry, blue- 

 berry, and cranberry, and of such trees as the chestnut and 

 pine, indicates poor drainage, and soil that is low in lime. 



