No. 7. DEPARTMENT OF AGRICULTURE. 457 



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about 16 cents, were added to each ton of manure and 8 tons of 

 manure per acre were applied for a three-year rotation of corn, 

 wheat and clover, the value of the increase in crop yields was equal 

 to $2.66 for each ton of manure used, in case of yard manure (which 

 was worth only |1.64 per ton without the phosphate), and, in case 

 of the stall manure, its value was increased from |2.22 a ton to $3.42 

 by the addition of the 16 cents' worth of rock phosphate, these re- 

 sults being the average of nine years' experiments on three different 

 series of plots, based upon increased yields valued at 35 cents a 

 bushel for corn, 70 cents for wheat and $6 a ton for clover hay. 



If we deduct the cost of the phosphate used, we still have what 

 might be termed a net value of $2,50 for the phosphated yard ma- 

 nure, and |3.24 a ton for the phosphated stall manure. 



Of course it would be equally appropriate, and possibly more so, 

 to speak of "manured phosphate," instead of "phosphated manure," 

 because the rock phosphate actually furnishes the needed deficient 

 element, phosphorus, while the manure helps to make it available. 

 On this basis we may say that the value of 40 pounds of rock phos- 

 phate is increased from 16 cents to $1.02 by mixing it with a ton of 

 yard manure and from 16 cents to $1.20 by mixing it with a ton of 

 stall manure, after deducting the value of the untreated manure in 

 each case. 



The most important fact to keep in mind, however, is that both 

 the manure and rock phosphate are much more valuable when used 

 together than when used separately, because manure is deficient in 

 phosphorus and rock phosphate does not act except in connection 

 with rotting organic matter. As a rule it is better to use sufficient 

 rock phosphate with each ton of manure so as to supply about 200 

 pounds of rock phosphate per acre for each year in crop rotation (a 

 good grade of raw rock phosphate contains at least 12^ per cent, 

 of the actual element, phosphorus, which is equivalent to 28 per 

 cent, of so-called "phosphoric acid"). 



There are two very satisfactory methods of mixing the rock phos- 

 phate with manure. One is to sprinkle the phosphate over the ma- 

 nure from day to day as it is being made in the stall or covered 

 shed. The other method is to fill the spreader part full of manure, 

 then sprinkle phosphate over it sufficient for the road, finish loading 

 with manure and drive to tli^e field and spread. This produces an in- 

 timate mixture and a very uniform distribution, and repairs prac- 

 tically no extra work to get the phosphate on the land. Care should 

 be taken that the manure is not too dry when the phosphate is 

 sprinkled over the load, otherwise the dry rock dust may get into 

 the gearing or bearings of the spreader and cause them to wear 

 rapidly. 



There are some extraordinary or abnormal soils. Thus, there are 

 soils exceedingly rich in nitrogen and well supplied with phosphorus 

 but very deficient in potassium; as, for example, certain peaty swamp 

 soils on which the application of potassium induces an increase in 

 the corn crop usually amounting to more than 30 bushels per acre, 

 and on which Illinois farmers are already using about $20,000 worth 

 of concentrated potassium salts annually, and with a net profit of 

 more than 200 per cent. 



There are soils exceedingly rich in phosphorus and well supplied 



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