130 The Potato 



FARM MANURES 



Farm manures increase the productiveness of the soil 

 in four ways : first, by the actual plant-food added to the 

 soil ; second, by the physical effect of loosening and 

 aerating the soil and adding to its moisture-holding ca- 

 pacity ; third, by the action of the organic matter of the 

 manure in making available to the plants by its decay the 

 insoluble plant-food of the soil ; and fourth, by improving 

 the soil conditions for the work of the beneficial bacteria. 

 Any computation based on the trade value of the plant- 

 food may be falsified by the other values being even more 

 important. A better way is to consider the results ob- 

 tained in farm practice by particular crops through a 

 series of years long enough for the residual effect of the 

 manure on the soil to be measured. The potato usually 

 responds well to the use of manure throughout the humid 

 sections, and the increase in yield of a cash crop like the 

 potato gives quick returns for the use of the manure. 



There is some danger that common scab will be worse on 

 potatoes grown on land heavily manured. This danger 

 is reduced by using smaller amounts, by having the 

 manure rotted, and by spreading some time before plant- 

 ing. Horse manure is thought by some to favor scab 

 more than other manures, but this is doubtful. 



Manures are poorly balanced fertilizers. They contain 

 relatively much more of nitrogen than of the other 

 plant-food elements and are likely to produce plants 

 with large growth of tops without corresponding tubers. 

 This can be prevented by using with the manure 50 

 pounds of acid phosphate to each ton, and in rare 

 cases potash may be added also. Coarse and strawy 

 manure may make some soils too open and porous, 



