120 CONSERVATION AND IMPROVEMENT OF SOIL 



renders it more easily mixed with other fertilizer ingredients. It 

 is more expensive than the muriate. Some farmers have a notion 

 that it improves the quality of potatoes and tobacco. This belief 

 has not been well established experimentally. 



Kainit is one of the crude mined products and contains about 

 twelve per cent of potash (K 2 O). It is used to a limited extent, 

 particularly near eastern ports where the cost for shipment is 

 not too excessive for such a low grade of fertilizer. 



The Use of Fertilizers. There are several ways of determining 

 what fertilizers to use on each field for each crop. The actual 

 requirements of any given crop should be known. Tables show- 

 ing the composition of different crops will tell in a very definite 

 way the amount of nitrogen, phosphoric acid and potash removed 

 from the soil during its growth. If a wheat crop, for example, is 

 grown, and the straw used for litter and returned to the field, the 

 amount of plant food actually taken from the field and not re- 

 turned is represented in the composition of wheat grain which 

 may have been sold from that field. When the yield is known the 

 amount of plant food removed may be easily calculated. (See 

 tables in Chapter XII). 



Other indications of the amount of fertilizer to use are found by, 

 (1) analyzing the soil, (2) plot method of trial; (3) the observation 

 of growth and yield of the crop itself through a series of years. 



Soil Analysis. In some states it is a common mistake to put 

 too much dependence upon analyses of soils made by State Experi- 

 ment Stations and employed chemists. Such analyses are valua- 

 ble only as indicating the total amount of plant food of each of 

 the three or four main ingredients, but they do not indicate how 

 much of each of these is available for growth of plants. If the 

 analysis shows a superabundance of any or all of these elements 

 in a certain field, it may be a fair guide to the owner, when con- 

 sidered in connection with what he knows regarding its yielding 

 ability. But the analysis as an independent fact does not tell 

 him definitely what fertilizers to use. If, however, one of the 

 ingredients is shown by the analysis to be very deficient he will 

 know that such deficiency must be supplied. The range in com- 

 position of surface soils is so great that analysis serves as a guide 

 in detecting the great reduction of any one element. 



Plot Trial. A manager of a large farm should determine the 

 needs of each field by actual trials on small plots. For small 

 grains, grasses, corn and cotton, use small strips about one rod 



