444 MISCELLANEOUS FARM SUBJECTS 



in their requirements. The results obtained in one locality may be 

 inapplicable in another. 



Certain soils are naturally deficient in plant food even when 

 first placed in cultivation; they do not supply a sufficient quantity 

 of some one essential plant food to produce good crops. A great 

 many soils are naturally deficient in phosphoric acid. This is par- 

 ticularly true of sandy soils. 



If the store of plant food in the soil is drawn upon by crops and 

 the crops taken away, in time the fertility of even the richest soil 

 will be depleted unless the plant food is restored. A great many soils 

 which were originally very productive have lost their fertility in 

 this way. 



Changes are going on in the soil which convert materials con- 

 taining nitrogen into nitrates and ammonia. These can be taken up 

 by plants, while the original nitrogenous matter cannot, but nitrates 

 are very soluble in water and may be washed out of the soil. Under 

 clean cultivation a considerable loss of nitrogen has been known to 

 occur in this way ; sometimes as much as 60 pounds per acre. Such 

 loss would, of course, tend to deplete the store of nitrogen in the soil. 



Truck crops, which must grow rapidly and mature early, make 

 very heavy demands upon the soil for plant food. Even fertile soils 

 may not supply the necessary plant food with sufficient rapidity. 

 With crops of this nature the application of commercial fertilizers 

 is usually profitable. 



Some soils are deficient in one element and some in another; 

 and frequently a soil is found that is deficient in two elements, but 

 no soil is found that is deficient in all of the three elements nitro- 

 gen, phosphoric acid, and potash. Nitrogen is usually the most de- 

 ficient element in soils that are said to be getting "thin." 



Methods of management and cropping also exert an influence; 

 for example, soils of equal natural fertility may not respond equally 

 to uniform methods of fertilization, because in the one case a single 

 crop, requiring for its growth proportionately more of one of the 

 essential elements than of another, is grown year after year, and it 

 may be that the element required is the one that exists in the soil 

 in least quantity. On the other hand, crops may be grown that 

 demand but minimum amounts of the element in question ; hence its 

 application to the soil for the one crop may be followed by largely 

 increased returns, while for the other but little if any increase in 

 crop is apparent. 



In the matter of management, too, a considerable variation may 

 be observed. One soil may lose a large portion of its essential constit- 

 uents, because no pains are taken to retain for the use of the crop 

 the plant food annually rendered available through the natural 

 agencies of sun, air, and water ; while in another, by means of care- 

 ful cultivation and the use of absorbents and catch crops, the con- 

 stituents made available are largely retained. 



HOW TO DETERMINE THE REQUIREMENTS OF THE SOIL. 



One of the most common inquiries is, how the fertilizer re- 

 quirements of a soil may be determined. It is a very common and 



