136 MASS. EXPERIMENT STATION BULLETIN 162. 



out, the supply of phosphorus in the soils has decreased steadily under 

 the system of agriculture pursued, and is now steadily decreasing under 

 the most common farm practice. 



Conditions in Massachusetts are widely different : — 



1. The principal products sold from our farms are hay, vegetables, 

 fruit and milk. The latter is the only product which carries away much 

 phosphoric acid, and the proportion in this is small. The milk of 20 

 cows for one year (6,000 pounds each) will contain only about 100 pounds 

 of phosphorus. 



Timothy hay contains over four times as much potash as phosphoric 

 acid; medium red clover, five times; cabbages, four times; potatoes, six 

 times; and other vegetables in about the same proportion. In fruits the 

 amount of potash is about six times the amount of phosphoric acid. If 

 we reduce these figures to the basis of pliosphorus and potassium used 

 by Hopkins the comparison is yet more striking, for in the products chiefly 

 sold from Massachusetts farms the amount of potassium carried away 

 will run from eight to ten times the amount of phosphorus. 



2. Many farmers use a large amount of purchased feeds, nearly all 

 of which are very rich in phosphoric acid. This reaches our soils in the 

 manures from our cattle and horses. In the oats fed on the average to a 

 pair of work horses in one year there are about 40 pounds of phosphoric 

 acid, while in the purchased feeds for a herd of 20 cows it is pi'obable 

 that on the average we shall find 600 pounds of phosphoric acid. 



3. The potash of animal excrements is voided mostly in solution in 

 the urine (on the average, about four-fifths of the total). The phos- 

 phoric acid, on the contrary, is voided ahnost exclusively in the dung in 

 insoluble forms. Under ordinary systems of stabling our live stock and 

 saving manures the potash, therefore, is subject to loss in much greater 

 degree than the phosphoric acid. 



4. That the crops we principally grow take from our soils far more 

 potash than phosphoric acid has been made apparent from what has 

 been said of the relative proportions of these two elements in the products 

 sold. Essentially the same relation holds for the products mainly con- 

 sumed on the farm. 



5. In our agriculture we have used commercial fertilizers largely for 

 at least forty years. With few exceptions these contain much larger 

 proportions of phosphoric acid than of potash. It is impossible to present 

 exact figures, but it is the writer's judgment that on the average twice 

 as much phosphoric acid as potash has been generally apphed in the 

 fertilizers used. 



Does it seem likely, in view of the facts stated, that our soils are being 

 especially depleted in phosphoric acid? This can be true only if the phos- 

 phoric acid is subject to loss from our soils under the influence of natural 

 agencies in unusually large proportion. That this is the case is highly 

 improbable. Phosphoric acid cannot escape into the air; and in the 

 soil, even though soluble when applied, it soon enters into new com- 



