EXTENSIOlSr COURSE IN SOILS. 73 



leaving it in the rough plowed form gives frost and weather an oppor- 

 tunity to break down the clods, causing them to crumble. Care 

 must be taken not to attempt to work the land in the spring until the 

 surface is dried off enough to permit harrowing or disking without 

 causing puddling. 



Crops for clay soil. — On account of their fine texture and the diffi- 

 culty with which roots penetrate clay soils they are not well adapted 

 to such crops as have coarse roots, which can not readily enter the 

 soil. On the other hand, extremely fine roots of grass are able to find 

 their way into the most dense clays and can therefore take advantage 

 of the large water-holding capacity such soils possess. Small grains, 

 such as barley and wheat, do well on these soils for the same reason. 

 Vegetable and truck crops are, as a rule, very poorly adapted to 

 heavy soils, because their roots usually find difficulty in penetrating 

 the soil, especially in a climate characterized by frequent summer 

 rains. This soil is particularly objectionable for the growing of pota- 

 toes, since it is very difficult to prevent the soil from baking and 

 cracking after cultivation has stopped, thus permitting the sun 

 to strike the tubers and cause sun scald. When all of these factors 

 are taken into consideration, it is evident that such lands are best 

 adapted to the growing of cereals, corn, alfalfa, clover, and grass, and 

 that stock raising in which the grass is used for pasture is especially 

 adapted to them. 



Fertilizers. — Clay soils vary a great deal in chemical composition. 

 This applies to practically all elements of plant food. Since potas- 

 sium is almost always present in relatively large amounts, it is often 

 unnecessary to add potash fertilizers. The phosphorus content, on 

 the other hand, is frequently found to be comparatively low, as in the 

 case of the heavy clay soils occurring in the Lake Superior and Lake 

 Michigan region. Besides such soils frequently contain considerable 

 iron, which tends to reduce the availability of the phosphorus. For 

 this reason, and because heavy clays warm up rather slowly and 

 vegetation is apt to be slow and backward, particularly in the spring, 

 a good supply of this element in available form is desirable in such 

 soils. The element phosphorus has a very marked effect in hastening 

 the maturity of practically all crops, so that it is often possible by 

 the use of moderate applications of phosphate fertilizer on cold soils 

 to cause crops to mature from one to two weeks earlier than they would 

 otherwise do. The amount of nitrogen in such soils is extremely 

 variable. In many cases a considerable supply of organic matter 

 containing this element occurs in clay soils as a result of their more 

 or less marshy condition before drainage. This condition permitted 

 the growth of considerable native vegetation, but lessened its decom- 

 position. Soils of this character are usually found well supplied with 

 nitrogen after drainage and cultivation. It often happens, however, 



