20 FOR BETTER CROPS IN THE SOUTH 



It will be seen that potassium increased the yield of corn by 

 more than sixty bushels to the acre. It should be understood 

 that some soils which are peaty in the surface with a heavier 

 clayey subsoil within reach of the plow can be improved merely 

 by deep plowing, for the clayey material is usually rich in 

 potassium. It sometimes occurs that a subsoil exists which 

 contains considerable amounts of total potassium, but this may 

 become available slowly unless more actively decaying organic 

 matter than peat is present. In such cases even light applica- 

 tions of fresh farm manure may produce an effect far exceeding 

 that which is commonly expected. 



Occasionally peaty swamp soils, like other soils, may contain 

 some injurious alkali, as magnesium carbonate, in the sub-sur- 

 face soil in such amounts as to prevent corn roots from living 

 in it, and hence liberal amounts of available potassium provided 

 in the surface soil may greatly benefit the crop. Deep peat and 

 peat underlaid by clean sand are, as a rule, deficient in both 

 available and total potassium. 



It is well to remember that the seed or grain contains only 

 about one-fourth of the potassium required for a crop, while three- 

 fourths remains in the straw or stalks; also that animals retain 

 practically none of the potassium consumed in the food, almost 

 all of this element being returned in the solid and liquid manure. 



Calcium — As an average, the normal soils of central United 

 States contain only one-third as much calcium as potassium; 

 while the average annual loss of calcium in drainage waters and 

 in crops removed amounts to five or six times as much as the 

 loss of potassium; so that in the maintenance of plant food the 

 addition of calcium in limestone is of very much greater impor- 

 tance than is the application of potassium to the almost inex- 

 haustible supply now present in such soils-. 



Magnesium — The amount of magnesium required by crops 

 is appreciable, but not nearly so large as of the other four ele- 

 ments mentioned. Magnesium can be applied most cheaply and 

 in readily available form by using dolomitic limestone. Dolomite 

 contains about as much magnesium as calcium, and has slightly 

 greater power to correct soil acidity than the ordinary high 

 calcium limestone. 



Making Plant Food Available — lu is an absolute essential 

 in agriculture to have plant food in the soil. If it is not present 

 in abundance it should be supplied in the manner that is most 

 economical and profitable, and .that which is removed in crops 

 should be replaced so far as practicable and profitable, either by 

 returning it in farm manure, or by plowing under green manures, 

 corn stalks, straw, and other coarse products, and by adding 

 phosphate and limestone. 



