AGEICULTURAL CHEMISTRY. 171 



especially in presence of lime or alkalies, or perhaps under other 

 conditions as ammonia. 



As to the amount of assimilable matters needful to constitute a 

 fertile soil, we have hardly any just notion, nor, indeed, can we easily 

 form one. 



If we assume Avhat is as yet not altogether warranted, the right 

 of distinguishing between the assimilable and non-assimilable parts 

 of the soil by the solvent action of carbonated water, we still en- 

 counter the variable influence of physical characters as affecting the 

 distribution of the plant-food, and above all, there stands in our way 

 the capital fact that as the growth of the plant is progressive, so are 

 its wants, and likewise those solving mediating agencies which supply 

 its food. So that we cannot, hj observations made at any one mo- 

 ment, determine the value of ingredients which extend their action 

 over a considerable period of time. 



The same soil may vary exceedingly at different times in its con- 

 tent of soluble matters, as analysis has proved. In the garden soil 

 above alluded to the content of nitric acid given is that found in 

 June; but Boussingault informs us that in the following September 

 the same earth contained near thirty times as much of this ingredient. 



There is doubtless a rigorous reciprocal relation between the 

 quantities of soluble (assimilable) matters in the soil and the mass 

 of soil needed to feed a plant during the vegetative period. 



The greater the proportion of soluble matters, the less volume of 

 earth is neeeded to sustain a given crop. In practice it is found that 

 each kind of plant requires a certain and pretty large quantity of 

 soil for its development. The farmer has his rules as to the space 

 which shall intervene between individual plants of wheat, of potatoes, 

 of maize, &c; and in regions widely distant from each other these 

 rules, adopted as the best result of experience, are more or less 

 unlike, varying with climate, soil, and other circumstances. It is 

 found, also, that on a given soil nearly the same crop is obtained, 

 whether the plants be closer to, or farther from each other, within 

 certain limits. In case of fewer plants, each one is more vigorous, 

 and gives a larger return; while in the other instance, the smaller 

 individual yield is made up by the greater number of plants. 



Boussingault, to whose numerous and admirable researches the 

 student of scientific agriculture must constantly make reference, 

 found by actual measurement that, according to the rules of garden 

 culture as practiced near Strasburg, a dwarf bean had at its disposition 

 65 pounds of soil; a potatoe plant, (hill?) 190 pounds; a tobacco 

 plant, 480 pounds; and a hop plant, 3,000 pounds. 



In respect to chemical composition, we may assert that the absence 

 of several, or even of one essential form of plant-food, must stamp 

 a soil with utter infertility, no matter how abundant its other ingre- 

 dients may be. It is equally true that the absence of one ingredient 

 in assimilable condition must constitute a soil barren and worthless. 



We may likewise lay down the proposition that the deficiency, vp to 

 to a certain point, of one or several substances in available form, 

 renders a soil infertile. On the other hand we cannot, with any 



