390 



THE SOUTHE 



RN PLANTER 



[July 



of earthy phosphates not fixed by the soil^ 

 must become saturated with these phosphates, 

 nd thus convert them into a condition in 

 hich they can be diffused through the 

 "ound. If the earthy phosphates, when 

 ,lius diffused in solution, come in contact 

 with other portions of soil not yet saturated 

 with these salts, those portions absorb and 

 fix these earthy phosphates, and the chloride 

 of sodium or nitrate of soda retains, a second 

 time, or more frequently, the power of ex- 

 ercising the same solvent and distributing 

 action over the earthy phosphates until the 

 ultimate and complete conversion of the 

 chloride and nitrate into a lime or magnesia 

 salt. 



When we consider how much the fertili- 

 sing effect of bone earth is increased by the 

 greater solubility and capability of distribu- 

 tion in the soil communicated by the action 

 of sulphuric acid, we cannot too highly esti- 

 mate the significance of the properties, just 

 described, of the salts of ammonia, chloride 

 of sodium, and Chili saltpetre. 



The most abundant application of earthy 

 phosphates in coarse powder, can in its ef- 

 fects bear no comparison with a much small- 

 er quantity which, in an infinite state of divi- 

 sion, is dispersed through every portion of 

 soil. A rootlet requires at the spot where 

 it touches the soil a most minute amount of 

 food ] but it is necessary to its functions and 

 its very existence, that this minimum be 

 found exactly at this spot. For if the food 

 of plants be not soluble in water, then is any 

 excess at any other spot as valueless to the 

 function of nutrition of this rootlet as if it 

 did not exist at all in the soil. Now, the 

 salts of which we have been speaking, pos- 

 sess the property of conveying these ele- 

 ments of food from the spot in which they 

 exist in superabundance to others in which 

 there is a deficiency ; and even though their 

 elements contributed in no way directly to 

 the process of nutrition, yet, these salts must 

 nevertheless exercise a marked influence on 

 the increase of produce. 



When the sulphate of ammonia and Chili 

 saltpetre have been completely transformed 

 into lime and magnesia salts, and the chlo- 

 ride of sodium into chloride of calcium and 

 chloride of magnesium, this action then 

 ceases ; and a second dose of these salts is 

 then necessary to reproduce the action. 



If the effect of the salts of ammonia de- 

 pends on the ammonia, we can scarcely com- 

 prehend why, after a large application of 



them, that portion which has not acted dur- 

 ing the first year should not in the second 

 come into operation, since this latter portion 

 is presented in the soil to plants in the same 

 form as the portion which produced its effect 

 during the first year. 



Sulphate of ammonia produces on alka- 

 line silicates a reaction similar to that on 

 earthy phosphates If this salt, in very di- 

 lute solution, is brought in contact with soil 

 saturated with silicate of potash, and which 

 does not give up a trace of its potash to 

 water alone, it instantly di|solves a certain 

 quantity of this alkali, which may be easily- 

 detected by the ordinary re-agents. 



It is evident that the agriculturist, by the 

 proper application of the chemical action of 

 common salt, Chili saltpetre and ammonia 

 salts, accomplishes the same object as by the 

 mechanical operation of ploughing, and by 

 the action of the atmosphere in fallow. 



We should be committing an error, if, 

 judging from similarity of solvent proper- 

 ties, we concluded that common salt must 

 have the same effect as a corresponding quan- 

 tity of nitrate of soda. We know that, as 

 a rule, in these cases, the common salt is 

 converted into chloride of calcium, and the 

 Chili saltpetre into nitrate of lime ; and the 

 experiments of Kuhlmann have taught us, 

 that chloride of calcium by itself is abso- 

 lutely ineffective, or rather is hurtful in the 

 cultivation of plants, whilst nitrate of lime 

 contributes materially to the increase of a 

 hay crop. Nitrate of soda, consequently, 

 acts favourably in two ways ; chloride of so- 

 dium only in one. Further, land plants can 

 bear a considerable quantity of nitrates of 

 soda in the soil, whilst chlorine compounds, 

 beyond a certain very narrow limit, are de- 

 cidedly hurtful. 



We designate as manures all substances 

 which increase the produce of our fields, 

 without knowing whether many of these 

 may not simply act, by rendering the food 

 already existing in the soil more capable of 

 absorption and assimilation. The simple fact 

 of their favourable influence on vegetation, 

 is not yet a proof that they have acted di- 

 rectly as food. We compare the work which 

 the plough performs, to the mastication of 

 food, for which nature has provided animals 

 with a particular instrument ; and, as may 

 be seen from the experiments described 

 above, many substances, such as common 

 salt, nitrate of soda, and ammonia salts, in- 

 dependently of the action which is due to 



