MANURES 91 



(4) Add humus to the soil and increase its moisture holding- 

 capacity, also allowing freer circulation of air through soil. 



(5) Increase bacterial content of soil. 



*"It is probably fair to assume that asan average, 80 per cent of the 

 plant food contained in a ration passes on into the manure, and if the 

 manure is economically handled, a large portion of this plant food can 

 be gotten back into the soil, though as a matter of fact, it is pretty 

 difficult to avoid considerable loss, no matter how well the manure is 

 handled. A little carelessness may easily result in the loss of more 

 than half its value, since two-thirds of the nitrogen and four-fifths of 

 the potash in a ration are voided in the urine, and unless the liquid 

 manure is saved by absorbent bedding and a tight floor, the loss of 

 these elements is particularly heavy. The possible losses through 

 heating and leaching are equally serious and must be guarded against 

 with the utmost care. 



"The question is often asked what manure is worth, but it is evi- 

 dent from the foregoing statements that no definite value can be as- 

 signed. It is variable and depends upon the ration from which the 

 manure is made, the age and kind of animals, and the care given it, 

 and in general is closely proportional to the care. One ton ofmanure 

 of average composition contains plant food which it would cost $2.25 

 to replace in the form of the cheapest fertilizing materials, and that 

 valuation is perhaps as fair as any." 



The importance of manures as a source of humus is well shown by 

 an experiment at the Minnesota Station, where two plots, originally 

 similar, were cropped in the same manner except that one was ma- 

 nured and the other was not; At the end of 35 years the first contained 

 3.32 per cent of humus and a water-holding capacity of 48 per cent, 

 while the second contained 1.8 per cent humus and could hold but 39 

 per cent of moisture. 



At the Minnesota Station** a four and a five-year rotation, which 

 included corn, oats, clover, wheat, and barley, were compared with 

 the continuous growing of each of the cereals mentioned. Manure 

 was applied to the corn in the rotations, but the continuous cropping 

 plots received none. The experiment was continued for twelve years. 

 Excessive losses of humus and nitrogen, together with decreasing crop 

 yields, were found on each of the continuous cropping plots, while on 

 the manured rotation plots the yields and humus and nitrogen sup- 

 plies were maintained and in one case slightly increased. The corn 

 in the rotation yielded 20 bushels per acre more than that grown on 

 the plot which grew corn exclusively and continuously, 



♦Indiana Circular No. 25, Revised Edition 

 •♦Minnesota Bulletin No. 89 



