164 MASS. EXPERIMENT STATION BULLETIN 162. 



CONCLUSIONS. 



The principal points which have been presented that have a bearing 

 upon the questions affecting the need and selection of phosphates will 

 now be summarized. It is beheved all are either well grounded in general 

 knowledge and experience, supported by results of our own experiments 

 reported in earlier pages, or established by the experiments of others. 



1 . The products chiefly sold from Massachusetts farms contain relatively 

 little phosphoric acid; potash is contained in them in far larger propor- 

 tion, usually from four to six times as much. 



2. Most farmers use purchased stock or horse feeds rich in phosphoric 

 acid, and thus greatly enrich the manure made in that compound. 



3. Phosphoric acid is subject to much less waste from accumulating 

 manures under usual conditions than potash. 



4. The crops grown in our farm, garden and orchard practice all take 

 from the soil far more potash than phosphoric acid. 



5. The fertilizers in general use for the past fifty years have supplied 

 far more phosphoric acid than potash. 



6. Phosphoric acid is subject to extremely little loss from soils by 

 leaching. 



7. It seems clear from the preceding statements that under our system 

 of agriculture our soils are not being depleted in phosphoric acid. 



8. Chemical analysis of our leading soil types by conventional methods 

 shows that the percentages of acid soluble phosphoric acid and potash 

 are usually nearly equal; averages for the State, phosphoric acid, .214 

 per cent.; potash, .252. 



9. If all of these compounds found in our average surface soil by con- 

 ventional methods of analysis could be utihzed — 



The phosphoric acid would (according to crop) last from ninety-two to 

 eight hundred years. 



The potash would (according to crop) last from forty-two to two hun- 

 dred and ninety years. 



10. The total potash in the surface soil very materially exceeds the 

 total phosphoric acid, and acid soluble potash is usually much more abun- 

 dant in subsoils than phosphoric acid. 



11. In spite of the relatively greater stock of total potash in soils than 

 of total phosphoric acid, an application of the former in soluble forms in 

 fertilizers has produced larger crop increases than has a similar applica- 

 tion of phosphoric acid for the following: asparagus, potatoes, corn, hay, 

 clover and soy beans. The only crops giving larger increases on phos- 

 phoric acid are crucifers (turnips, cabbages, etc.). 



12. The results of hundreds of experiments at this station and in various 

 parts of the State indicate that phosphoric acid is not the key to "per- 

 manent" (successful and profitable) "agriculture" in Massachusetts. It 

 is not usually the element in minimo. Potash, as measured by crop re- 

 quirements, is more often in minimo, and determines the yield. 



