EXTENSION 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, 
