248 DRY FARMING 



tion or any of the causes that go to diminish the moisture 

 content of the soil. The fundamental cause of low 

 yield in another field may be insufficient available plant 

 food. The practical cause may have been an infertile 

 soil, unsuitable tillage, continuous cropping with no 

 return of plant food or any of the other causes that de- 

 crease or leave undeveloped the plant food in the soil. 



In this chapter we shall discuss the practical causes of 

 low yields because it is with these the grain grower is 

 most familiar and it is these he usually advances to ex- 

 plain why his crops are not satisfactory. Among these 

 are: 



198. Poor Seed. Poor seed is seed that will either not 

 germinate or will not grow vigorously, that contains dis 

 ease or impurities or that belongs to a variety that is not 

 suited to the district where it is to be grown. The vigor 

 of growth and percentage of germination can be deter- 

 mined by making a germination test. Its freedom from 

 impurities including most forms of disease can be told by 

 examining the seed or by its odor, but the presence of 

 some diseases can only be detected in the field before the 

 crop is harvested. The suitability of the variety to a 

 district cannot be foretold by examining the seed. This 

 point can only be determined from the experience of 

 other farmers or from carefully conducted tests. 



The seed may be so inferior that it will produce no 

 crop, it may be so good that it will result in maximum 

 returns or it may occupy any intermediate stage of per- 

 fection. No intelligent farmer takes chances on his seed 

 being the cause of decreased yield. This is one of the 

 factors of production that lies wholly within the power 

 of the farmer to control. 



199. Too Early or Too Late Seeding. The best time to 



