INFLUENCE OF BARNYARD MANURE AND WATER 

 UPON THE BACTERIAL ACTIVITIES OF THE SOIL 



By J. E. Greaves, Bacteriologist, and E. G. Carter, 1 Assistant Bacteriologist, De- 

 partment of Bacteriology, Utah Agricultural Experiment Station 



INTRODUCTION 



The application of barnyard manure to a soil brings about a far-reaching 

 change within the soil. It has been found that, as an average, i ton of 

 barnyard manure contains 10 or 12 pounds each of nitrogen and potassium 

 and 2 or 3 pounds of phosphorus. It also carries other substances of less 

 importance which may be directly utilized by the growing plant or which 

 may react with substances within the soil, changing their solubility. 

 This direct and indirect nutritive value of a manure is not its only function, 

 for it changes greatly the physical structure of the soil. It improves the 

 tilth of a clay soil by increasing the granulation within it, while in a sandy 

 soil it tends to bind the particles together, making it less porous. Each 

 of these changes react upon the water-holding capacity and the capillarity 

 of the soil, greatly altering the aeration of the soil and with it the tempera- 

 ture. 



The biological changes which the manure produces in the soil, especially 

 when small quantities are added, may be more far-reaching than either 

 the chemical or physical changes which it produces. Every pound of 

 manure carries with it to the soil millions of bacteria. Many of these will 

 find the new conditions unsuited for their growth, but some will continue 

 to multiply, and in so doing not only will decompose the constituents of 

 the manure but also will greatly alter other organic and inorganic sub- 

 stances of the soil. Hence, the bacterial content of the soil is changed 

 both quantitatively and qualitatively. There are added with the manure 

 many new species, and the changed physical and chemical conditions of 

 the soil due to the manure will greatly modify those already present, for 

 the microflora and fauna originally present in the soil were due to specific 

 properties of the soil. 



This changed flora and fauna will in turn change the chemical and phys- 

 ical properties of the soil still more. Acids are generated, which react 

 with insoluble constituents, rendering them soluble. Gases are formed, 

 which change the air within the soil; and in these reactions heat is gen- 

 erated, thus changing the temperature of the soil. The metabolism of 

 the bacterial cell requires nutritive substances, among which are water 



1 The authors wish to express their appreciation of the kindness of Dr. F. S. Harris, of the Utah Experi- 

 ment Station, in placing at their disposal the plots used in this investigation and also the records of treat- 

 ment and yield, for it is this assistance which has made possible this investigation. 



Journal of Agricultural Research, Vol. VI, No. 23 



Dept. of Agriculture, Washington, D. C Sept. 4, 1916 



fe Utah— 3 



(889) 



