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be continually returned to the soil in order that its fertility may be 

 maintained. These are Nitrogen, Phosphoric acid and Potash. In 

 this leciure Mr. Warington discusses the character of the nitrogen- 

 holding material in the soil under three heads, i. Ammonia ; 2. Nitrates ; 

 3. Nitrogenous organic matter. The relative and absolute amounts in 

 which they exist and the circumstances that control their increase and 

 decrease are given at length. He shows that while the two former are 

 the most readily available forms for plants, it is in the organic matter 

 of a soil that the great bulk of the nitrogen is stored up. The accu- 

 mulation or nitrogen in the surface soil tikes place to a greater extent on 

 prairie and pasture land than in arable soils ; and further Mr. 

 Warington says that "for the present we cannot, I think, affirm that 

 soils are enriched by the free nitrogen of the air, except through the 

 medium of a leguminous crop. A diminution of surface-soil nitrogen 

 takes place when organic matter is in excess and air freely penetrates 

 the soil, since the conditions are then most favourable to the growth of 

 those organisms whose function it is to ( xidise ihe nitrogenous organic 

 matter. Hence, the richest soils are those most liable to waste and 

 demand the greatest exercise of the farmer's skill to preserve their 

 condition. 



Lecture 3. Treats of a very important maker, viz. Nitrification, 

 or the conversion of the nitrogen of the soil humus into the soluble 

 nitrogenous food of plants. Schlosing and Miintz showed that this was 

 due to the action of an organized ferment and Warington by experi- 

 ments carried on simultaneously confirmed their conclusions. I'his 

 living micro-organism has been succesfuUy isolated and studied by 

 Dr. Fra-.ikland, Winogradsky and Mr. Warington. The most favour- 

 able conditions for this process of nitrification are here discussed at 

 length. Briefly, they are the presence of phosphates, a slightly alkaline 

 condition of the soil due to lime or other salifiable base, "a liberal 

 supply of oxygen, the absence of strong light " and a temperature about 

 98° F. We here find the explanation of the fact so well known, viz., 

 that the addition of marl or chalk (carbonate of lime) in moderate 

 amounts to a soil and especially to cne rich in humus, is of great value in 

 increasing crop yields. 



Lecture 4. Nitrification and Denitrification. — The conver- 



