ation of plant food; others do much harm, especially in causing 
“sick soils.” The most of them are microscopic in size; others 
can be seen with the naked eye, such as the beneficient earthworm 
which burrows through and feeds on the soil humus, letting in 
air and drawing down leaves and other debris from the surface. 
Beneficial soil organisms— These, fortunately for us, are readily 
controlled and their growth encouraged by certain proper agri- 
cultural practices. These beneficial organisms, in the first place, 
need a well-aerated, light, loamy soil for their best development. 
In a heavy, sticky, clay soil, devoid of humus, or a water-logged, 
sour, mucky soil, they will not grow. But in the soil made sweet 
by the addition of lime, well-stirred and oxygenated by cultiva- 
tion, with a plentiful supply of decaying vegetable matter 
(humus), and, finally, with a sufficient amount of mineral 
nutrients in soluble form, the beneficial soil organisms flourish, 
and the harmful ones are killed off or at least kept in the back- 
ground. 
The decay of platit and animal remains is brought about by 
beneficial bacteria and soil fungi; by this means, finally 
crumbling into dust, they again become dissolved in the soil 
water and thus available for plant food. Plant and animal 
bodies are composed of at least ten elements united into com- 
plex organic compounds: Carbon, Hydrogen, Oxygen, Nitrogen, 
Sulphur, Phosphorus, Potassium, Iron, Calcium , and Magnesium . 
Those in heavy type are the ones which are most apt to need 
replenishing in soils, and these the farmer often supplies to 
impoverished soils in the form of “artificial fertilizers.” Of 
course if he would add to his poor soils manures and plow in 
legumes, the final decomposition of these organic materials would 
supply all the necessary elements. Manures, however, are often 
poor fertilizers, from having been carelessly preserved and 
allowed to leach away and otherwise lose ammonia and other 
valuable materials. These losses may be reduced by compacting 
the manure and storing under shelter. 
Ammonification is the production of ammonia by bacteria and 
molds from manures and other decomposing organic bodies. 
This is accomplished by breaking-down processes comparable to 
digestions, performed by the enzymes secreted by certain bacteria 
and soil fungi. 
Nitrification is the breaking down of this ammonia, accom- 
plished by two very important sets of soil bacteria — the nihite 
and the nitrate bacteria. One group converts ammonia into 
nitrites; another changes the nitrites into nitiates, the only form 
of nitrogen which green plants can use directly. 
