ORGANIC MATTER 115 



It is interesting to note that fallow soil has a much higher 

 ammonifying power than has cropped, and this helps to account 

 for the good results obtained by fallowing in the arid regions. 



The speed with which proteins are ammonified varies also with 

 the soil. A rich sandy soil supplied with optimum moisture may 

 ammonify many times as fast as depleted soil or even a rich, tight, 

 clay soil. 



Moisture. — Ammonifying bacteria are similar to all other 

 plants in that they must have water in order to function. Their 

 activity increases as the moisure content of the soil increases until 

 a certain moisture content is reached. Above this concentration 

 there is a sharp drop in the ammonia production. This is at its 

 maximum in a soil when the moisture is 60 per cent of the soil's 

 water-holding capacity. This is one of the reasons why practical 

 farmers find that crop yields are best when the soil is kept moist 

 but not wet. 



Aeration. — The first stages of the breaking down of the pro- 

 tein is due to the microorganism causing water to enter into the 

 compound and then in some mysterious way to fall to pieces. In 

 the last stages, however, when ammonia is split oif oxygen enters. 

 Hence, we find that aeration increases ammonification. We find 

 ammonification rapid in fallow and the hoed crops as corn and 

 potatoes, but slow in oat and alfalfa soil. 



Reaction. — Acid soils ammonify slowly. Probably the small 

 amount produced is due mainly to molds. Either limestone or 

 lime added to such a soil accelerates the speed with which ammo- 

 nia is produced. Limestone soil usually ammonifies rapidly. 



Food Requirements. — ^The ammonifying bacteria break down 

 the proteins with the formation of ammonia in order to get the 

 energy necessary in their life processes. In addition to energy 

 they must also have certain elements which are essential to plant 

 growth. Phosphorus is required in large quantities by these organ- 

 isms, and a soil having large quantities of available phosphorus, 

 provided other conditions are ideal, has an active ammonifying 

 flora. 



The addition of starches, sugars, and other carbohydrates to a 



