Xn. 6. DEPARTMENT OF AT, raCULTURE. 363 



THE VALUE OF FAKM .MANURE AND UOW TO KETAIN IT, 



BY Fkof. Wells \V. Cooke, Washinoton, U. v. 



Farmers have for years recognized the fact that farm manures 

 have a value as a fertilizer for the plant food they contain, but it 

 is only within a comparatively short time that these same manui-es 

 have become valued for another quality, which, in many cases, h 

 fully as important as the fertilizing value. The first value is chem- 

 ical and depends on the chemical elements of plant food, the nitro- 

 gen, phosphoric acid and potash that are present; the second is 

 mechanical, and is due to the action of the manure on the soil. 



It is true that plants must have food to grow, but they must also 

 have a proper condition of the soil or they cannot use the plant food 

 in that soil. Farm manure is one of the best agents for putting the 

 soil in this correct condition. It loosens and lightens the soil, 

 making it porous, and letting in air and sunlight; farm manures are 

 great absorbers of water, one pound of dry matter holding from 

 four to seven poundsof water, and thus helping to tide the crop over 

 a drouth. "When the manure decays, much of it remains in the soil 

 as the black humus, and this has water-holding power in the highest 

 degree. As the stable manure decays it gives off carbonic acid, 

 though one of the weakest of acids, yet is strong enough to act 

 on the insoluble plant food of the soil and set some of it free for the 

 use of the plant. 



If soils contained no humus or vegetable matter they would be- 

 come so compacted that the roots of the plants could not penetrate 

 through them, and the crops would be failures. The air and sun- 

 light are continually acting on the vegetable matter, burning it up 

 and hence it is necessary to renew the supply, or the soil becomes 

 in a bad mechanical condition. The roots of plants, the stubble of 

 the grain, the sod of the meadow, all serve to add vegetable matter 

 to the soil. The plowing in of a green crop is the common method 

 in the South for increasing the supply of vegetable matter, but in 

 the North this is usually too exi)ensive, and farm manures are 

 relied upon to furnish the bulk of the humus needed by the crops. 



The heavier a soil is, i. e. the more clay it contains, the greater the 

 need of the lightening and loosening effects of farm manures, and 



