SOIL FERTILITY AND PLANT GROWTH 241 



teria, many of which aid in plant growth. Attention has 

 already been called to the fact that the addition of manure 

 improves the physical condition of the soil, making it more 

 porous, and increasing the supply of humus. 



Preventing loss from manure. Loss of fertilizing 

 qualities from manure is due principally to two causes : ( 1 ) 

 fermentation, or heating, which reduces the supply of nitro- 

 gen ; and (2) weathering, or leaching from rains, in which 

 all the valuable elements suffer. 



The fermentation of manure is caused by two different 

 kinds of bacteria, one of which works near the outside of 

 the heap where there is air, and one farther in where the 

 air is excluded. A certain degree of fermentation is neces- 

 sary to the best rotting of the manure, yet overheating, or 

 the "fire-fanging" so common in horse and sheep manure, 

 greatly reduces its value. 



The rapidity of fermentation can be controlled in part 

 by packing. If the heap is too loosely built, the air-working 

 bacteria become active, the heat grows intense and nitrogen 

 and humus-making material are lost. If, on the other hand, 

 the heap is packed too closely, the decomposition is slow 

 and the manure does not have the best effect when spread 

 on the soil. Frequent sprinkling with water will aid in 

 checking too rapid fermentation. 



Great loss is suffered from leaching when manure is ex- 

 posed to the weather. It has been found that six months' 

 leaching of horse manure reduces its value fully one-half. 

 The remedy lies in collecting manure under cover, so that 

 it is not exposed to rains. It should also be provided with 

 a water-proof floor for the heap, so that the liquid parts, 

 which are fully as valuable as the solid, may not drain away 

 into the soil. The profits from open-yard, badly leached 

 manure are so small as hardly to pay for spreading it on 



