76 The Sugar-Beet in America 



a green-manure. With this combination, the produc- 

 tivity of the soil should not only be kept up but should 

 actually be increased. 



HOW TO DETERMINE FERTILIZER NEEDS 



In order that there may be no waste of material, it is 

 important to know just what are the fertilizer needs of 

 the soil. This problem is not so simple as it might at 

 first seem to be. Soon after the methods by which 

 plants feed and the elements they require from the soil 

 were discovered, it was thought that by making a chemical 

 analysis of the soil, its fertilizer requirements could be 

 determined at once. It soon was found, however, that so 

 many factors entered into the problem that this method 

 could not be relied on. For example, an analysis may 

 show a soil to be rich in potassium and at the same time 

 this soil may give a marked response to the addition of 

 potash fertilizers. This is true for all plant-food ele- 

 ments. In some cases, the elements shown by a chemical 

 analysis to be lowest in the soil are the ones that give 

 least returns when added as fertilizers. Numerous exper- 

 iments have shown that an analysis of the soil is useful 

 when taken with other tests, but that alone it is not 

 sufficient. 



Field tests carried over long periods of time have been 

 found necessary in making a thorough diagnosis of the 

 needs of a soil. These may be supplemented by pot 

 tests and by chemical analyses. A complete understand- 

 ing of a soil cannot be obtained without a combination 

 of field and laboratory tests. When all this information 



