EFFICIENCY OF FERTILIZERS 363 



It will be seen from this table that the combination 

 of stall manure and rock phosphate produced larger 

 crops than did the same quantity of stall manure alone; 

 from which it may be fairly concluded that, under these 

 conditions, the raw phosphate becomes available to an 

 extent sufficient to make its use practical. Whether 

 raw phosphate can be used without supplementing 

 them with superphosphate will depend upon the natural 

 fertility of the soil and the amount of decomposing 

 organic matter it contains. 



231. Structure or tilth of the soil. Tillage aids the 

 plant in several ways to obtain nutrients from ferti- 

 lizers added to the soil: (1) By promoting aeration. 

 (2) By permitting the plant-roots to come in contact 

 with a large area of soil. (3) By conserving moisture 

 in time of drought. 



232. Cumulative need for fertilizers. It is often 

 remarked that on fertilized soils there is a gradually 

 increasing need for greater quantities of fertilizers. 

 This is doubtless the case in many instances, and arises 

 from neglect of other factors affecting soil productive- 

 ness. As we have seen, certain fertilizers induce a loss 

 of lime from the soil, which, if allowed to continue/'equires 

 an increased amount of fertilizer to maintain the yield 

 of crops. Organic matter is allowed to decrease and this, 

 as well as loss of lime, causes the soil to become compact 

 and poorly aerated, and so, one bad condition leading 

 to another, crops become poorer in spite of increased 

 applications of fertilizer. 



233. Farm manures. The original components of 

 farm manure are the solid excreta from the animal, the 



