252 SOILS AND FERTILIZERS 



If there is a good stock of natural fertility in the soil 

 and it is well tilled, with farm manures used and the 

 crops systematically rotated, commercial fertilizers will 

 not be needed. With poor cultivation and a soil that 

 has been impoverished by injudicious cropping, they 

 are necessary. Commercial fertilizers sometimes fail 

 to give good results because of an excessively acid or 

 alkaline condition of the soil. 



303. Amount of Fertilizer to use per Acre. --When 

 commercial fertilizers are used in general farming, just 

 enough should be applied to produce normal yields. 

 Heavy applications at long intervals are not so pro- 

 ductive of good results as light applications more fre- 

 quently. 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 contact 

 with seeds, neither should it be plowed under nor worked 

 into the soil to such a depth that it may be lost by leach- 

 ing before it can be appropriated by the crop. 



304. Excessive Applications of Fertilizers Injurious. - 



An overabundance of plant food has an injurious 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 



