72 BULLETIN 355, U. S. DEPARTMENT OF AGEICULTURE. 



spring. They usually have a high content of potassium, and the 

 phosphorus content is sometimes large. Their treatment, therefore, 

 must be such as to overcome their peculiar difficulties and take 

 advantage of their particularly strong points. 



Drainage. — Since large portions of these heavy clay soils were 

 formed as deposits in standing bodies of water, they very commonly 

 have comparatively level surfaces. They therefore frequently have 

 poor surface drainage as well as poor underdrainage. For general 

 farming everything possible must be done to secure good surface 

 drainage when the expense of tile is unwarranted. Tile drainage, 

 however, is often necessary in order to permit the use of such land 

 for crops requiring considerable tillage. This form of drainage for 

 such land is usually profitable, even for staple crops. The expense, 

 of course, varies, depending on the distance to an outlet, the presence 

 of stones in the subsoil, and other factors. Ordinarily the expense is 

 between $20 and $30 per acre. Since a tile system once carefully 

 installed in clay soil will last almost indefinitely, the expense to be 

 charged to the land is simply that of the interest on the investment, 

 or from $1.50 to $2 per year. Indeed, the entire expense is very 

 commonly recovered by the increase of crops in from one to three 

 years. 



Tilth.— The most serious difficulty in the management of heavy 

 clay soils results from their poor tilth. Such soils are apt to bake 

 and form large clods, so that preparation of a good seed bed and the 

 cultivation of the crop is difficult and involves much extra labor. 

 This poor tilth is due to the fact that the films of water surrounding 

 the fine grains draw the particles so closely together when they dry 

 that they are held with considerable tenacity. This difficulty may 

 be overcome to a limited extent by increasing the amount of organic 

 matter. Humus and vegetable matter in such soils has the effect of 

 lessening the tendency to form clods. Thus, after a heavy clay soil 

 has grown a crop of clover, or has been in grass for some time, it is 

 easier to retain a good tilth than if it is kept in tilled crops con- 

 tinually. As before shown, liming of clays, especially with quick- 

 lime, produces a flocculating effect upon the soil and so reduces the 

 tendency to clodding and greatly improves its tilth. Another 

 extremely important factor is the moisture condition when they are 

 cultivated. As before stated, when such soils are plowed or other; 

 wise worked in a wet condition, they have a marked tendency to 

 puddle and run together in such a way that very hard and resistant 

 clods are formed. It is extremely important to do all the work of 

 tillage on such land when the soil is in just the right condition of 

 moisture, so that the clods will break down in the soil. This condi- 

 tion must be determined for each individual field and with a little 

 practice can readily be recognized. Plowing clay land in the fall and 



