132 MASS. EXPERIMENT STATION BULLETIN 162. 



4. Notwithstanding the fact that potash is usually the more important 

 of the two the use of phosphoric acid in our agriculture is generally profit- 

 able, as will be shown bj^ the results of experiments presented. 



5. It will be shown that when both dissolved and fine-ground natural 

 rock phosphates are annually appUed the former have given both the 

 larger and the more profitable crop increases over a long series of years. 



6. It will be shown that although more than 1,600 pounds per acre of 

 phosphoric acid in the form of natural rock phosphates have been apphed 

 in a series of experiments extending over eighteen years, the yields on 

 these plots at present are even more inferior to the yields on plots receiv- 

 ing the same amount of phosphoric acid in the more soluble phosphates 

 than in the earlier years of the experiments. 



7. It will be shown that the dissolved phosphates have exerted certain 

 highly important secondary effects, among the more important being: — 



(a) Stimulation to rapid early growth both of root and top, which 

 secures, among other important advantages, sufficient root growth to 

 more surelj^ draw from the soil from the start both the water and the 

 food needed, and ability better to resist insect injuries. 



(6) Earlier and more perfect maturity, which may mean a much higher 

 price for the product, as in market gardening, or immunity from frost 

 damage in the case of late ripening crops or cold summers. 



(c) It will be pointed out that the work of others appears to demon- 

 strate the following additional secondary effects following the judicious 

 use of dissolved phosphates: increased tillering of grain and grasses; 

 increased availability of some important soil constituents; greater ac- 

 tivity of nitrifying organisms in the soil; and larger soil gain in atmos- 

 pheric nitrogen as a result of increase in assimilation of this element by 

 micro-organisms in the soil. 



8. Results will be presented which indicate that reasonable use of an 

 acid phosphate does not increase the necessity for application of lime, — 

 indeed, that in the experiments cited it appears to have had the opposite 

 effect. 



9. The final conclusions drawn from a consideration of all the facts and 

 results discussed may be thus stated: — 



(a) In Massachusetts agriculture it usually pays to use phosphoric 

 acid containing fertilizers in at least moderate amounts. 



{b) The more soluble phosphates are better adapted to our needs than 

 the fine-ground natural rock phosphates. Among materials ordinarily 

 used for supplying phosphoric acid only, usually most available and satis- 

 factory, are acid phosphate, dissolved bone black and basic slag meal. 

 Almost all mixed and special complete fertilizers contain liberal amounts 

 of soluble and available phosphoric acid. Other sources of phosphoric 

 acid in soluble or fairly available forms are dissolved bone, bone meals, 

 tankage and fish, all of them also supplying some nitrogen. 



