MANURE 213 



yet considerable quantities of nitrogen, phosphorus, and potassium 

 are lost in shrinkage. 



3. The loss varies widely in stored manures, depending upon 

 the conditions of storage. Light, porous, dry piles burn out much 

 faster than do compact, wet piles. This is due to the rapid oxi- 

 dation which goes on in the well-aerated piles. This at times is 

 sufficient to burn out most of the organic matter and leave the 

 remainder as a black charred mass. Manure piles subjected to 

 the leaching of rain lose in plant-food faster than non-exposed 

 piles. For this reason the loss in the humid districts is greater 

 than in the arid. On the other hand, probably manure in the 

 arid regions burns out faster than similar manure in the humid 

 regions. 



Value. — li^he value of barnyard manure varies with the com- 

 position of the manure, and the soil on which it is to be used, and 

 the kinds of crops to be grown. The valuable constituents within 

 it are the phosphorus, potassium, and nitrogen which are probably 

 worth about the same as similar quantities in the form of com- 

 mercial fertilizers. In addition to this, however, manure contains, 

 organic matter which influences the physical properties of the 

 soil and also furnishes food for bacteria. These in turn render 

 available more plant-food from the soil to fix nitrogen from the 

 atmosphere. The benefit derived in this latter case will vary with 

 the composition of the soil. A soil containing considerable in- 

 soluble plant-food will respond better to small quantities of ma- 

 nure than will another soil containing small quantities of insolu- 

 ble pknt-food. 



The results of the Pennsylvania Station indicate that in a good 

 rotation the average value of manure was $1.65 per ton where 

 twelve tons per acre are used, $1.32 where sixteen tons are ap- 

 plied, and $1.14 where twenty tons were applied for each four 

 years' rotation. This would correspond to an annual application 

 of 3, 4 and 5 tons, respectively. 



The work at the Rothamsted Station, which extended over a 

 period of half a century, clearly demonstrates that fourteen tons 

 per acre of farmyard manure will maintain the productivity of 



