AVAILABLE NITROGEN OF THE SOIf.. S8.^ 



ing of their indirect nutritive influence upon vegetation. 

 By these chemical transformations the organic nitrogen 

 may pass into the two compounds wliich, in the present 

 state of knowledge, we must regard as practically the ex- 

 clusive feeders of the plant with nitrogen. The rapidity 

 and completeness of the transformation depend upon 

 circumstances or conditions which we vinderstand but im- 

 perfectly, and which are extremely important subjects for 

 furtlier investigation. 



Difliciilty of estimating ttic Available Nitrogen of any 

 Soil. — The value of a soil as to its j^ower of supplying 

 plants with nitrogen is a problem by no means easy to 

 solve. The calculations tliat have just been made from 

 the analytical data of Boussingault regarding the soil of 

 his garden are necessarily based on the assumption that 

 no alteration in the condition of the nitrogen could take 

 place during the period of growth. In reality, however, 

 there is no constancy either in the absolute quantity of 

 nitrogen in the soil or in its state of availability. Por- 

 tions of nitrogen, both from the air and from fertilizers, 

 may continually enter the soil and assume temporarily the 

 form of insoluble and inert organic combinations. Other 

 portions, again, at the same time and as continually, may 

 escape from this condition and be washed out or gathered 

 by vegetation in the form of soluble nitrates, as has al- 

 ready been set forth. It is then manifestly impossible to 

 learn more from analysis, than how much nitrogen is avail- 

 able to vegetation at the moment the sample is examined. 

 To estimate with accuracy what is assimilable during the 

 whole season of growth is simply out of the question. 

 The nearest approach that can be made to this result is to 

 ascertain how much a crop can gather from a limited vol- 

 ume of the soil. 



Brctschneidcr's ExperinicntSt — We may introduce here 

 a notice of some recent researches made by Bretschneider 

 in Silesia, a brief account of Avhich has appeared since the 



