222 SOILS AND FERTILIZERS 



they have never been used. If the soil is properly 

 tilled and there is a good stock of natural fertility, the 

 use of commercial fertilizers can be avoided. With 

 poor cultivation and a soil that has been impoverished 

 by injudicious cultivation their use is more necessary. 



286. Amount of Fertilizer to Use per Acre. — When 

 commercial fertilizers are used, it should be the aim to 

 apply just enough to produce normal yields. Heavy 

 applications at long intervals are not as productive of 

 good results as light applications more frequently. 

 From 400 to 600 pounds per acre is as much as should 

 be used at one time unless previous trials have shown 

 that heavier applications are necessary. The way in 

 which the fertilizer is to be applied, as broadcast or 

 otherwise, must be determined by the crop to be 

 grown. The fertilizer should not come in direct con- 

 tact with seeds, neither should it be worked into the 

 soil to such a depth that it may be lost by leaching 

 before it can be appropriated by the crop. 



287. Excessive Applications of Fertilizers Injuri- 

 ous. — An overabundance of plant food has an inju- 

 rious effect upon crop growth. Plants take their 

 food from the soil in dilute solutions, and when 

 the solution is concentrated abnormal growth results. 

 Potatoes heavily manured with nitrate of soda make a 

 luxuriant growth of vines but produce only a few 

 small tubers. When a medium dressing is used along 

 with potash and phosphoric acid, a more balanced 



