How LEGUMES HELP THE FARMER 165 



by the acid condition caused by the humic acids present in the muck, and the 

 absence of alkaline bases. The addition of lime to the soil furnishes this 

 alkaline base, and nitrification will go on rapidly in the presence of an abund- 

 ant supply of carbonate of lime. That is, a supply in proportion to the 

 amount of organic matter present; for if in too great amount, the process 

 may be checked almost permanently, as has frequently been experienced 

 by our farmers who have used shell marl to excess on lands deficient in 

 organic matter. 



Another important condition for the rapid formation of nitrates is the 

 best temperature. While it has been found that the process will go on at a 

 quite low temperature, and, in fact, all winter in sections where the soil 

 does not freeze deeply ; it is far more active during 'the heats of summer, pro- 

 vided the temperature is not too high and there is plenty of moisture. It 

 is entirely checked at a temperature of 131 degrees Fahrenheit, and in per- 

 fectly air-dry soil. 



Strong light, such as direct sunshine, retards nitrification in the soil; 

 shading the soil with any sort of cover promotes more rapid accumulation of 

 nitrates. Hence the top dressing with manure not only makes a mulch to 

 retain moisture in the surface soil, but also, by means of the shading, it pro- 

 motes the nitrification of the organic matter in the soil, though, at the same 

 time, there will be a check to the nitrification of that part of the manure 

 fully exposed to the sun. 



NITRIFICATION AND ITS PRODUCTS. 



Nitrification, or the formation of nitrates in the soil, is the result of the 

 power possessed by certain microscopic plants of the great class known by 

 the general name of bacteria, to oxidize the ammonia, or organic matter, in 

 the soil ; and, through the energy thus produced, to get for their own use the 

 carbon in combination in the soil. The result of the oxidizing influence of 

 these plants is the production of nitric acid, carbonic acid, and water, but 

 whether these are all the result of the activity of one form of mico-organism 

 or not is as yet unknown. For many years some of the most accurate in- 

 vestigators in this country and in Europe have been engaged in the study 

 of the organisms that transform organic nitrogen into nitrates. These 

 investigations have proved that there is more than one kind of microbe en- 

 gaged in the work. ( "Remember that a microbe, or bacterium, is a plant and 

 not. an animal.) One form feeds on ammonia and transforms it into nitrous 

 acid, making nitrites, and can go no further. Another form then takes up 

 the work of oxidation and from these nitrites forms nitric acid, and hence 



