COLONIAL MUSEUM AND LABORATORY.

19

D—.No. 14

SOILS. Introduction. The following report on the composition of the soils in different parts of the Colony has been prepared, by direction of the Government, for the information of practical agriculturists. Tho assistance which is afforded by a knowledge of the component parts of soils, as ascertained by their chemical analysis, is now generally acknowledged. It is true that mere analytical results, without local knowledge, is not sufficient to prescribe in every case the course of treatment by which the soil may be rendered most fertile ; frequently, however, certain prominent wants in soils, and mode of treatment for increasing their fertility, are directly suggested by chemical analysis. For the general principles upon which chemistry is applied to agriculture the reader is referred to the standard works on the subject by Baron v. Liebig, Professor Johnston, and other writers. The principal object of this report is to enable the settler in New Zealand to apply these principles by affording the data necessary for enabling him to compare the soil with which he has to deal with the examples given in those standard works. With the view of making the information as complete as possible, the appended instructions were issued for collecting samples of soil with the accompanying questions. The answers sent with each specimen have been epitomized and embodied in this Report. Thirty-three of the samples of soil received have been analyzed by Mr, Skey, upon a method which is fully explained in the first section of the report. Tho results obtained have been arranged in a table (No. V.) in a form which renders them at once practically intelligible, and the principle of the construction of which is fully described. And lastly, a few practical deductions have been made, intended to assist the reader in referring to the works which treat at length on the subject of soils. Tho soils already analyzed probably represent most of the leading varieties which occur in the Colony, and therefore it will be unnecessary to extend the series of exact and exhaustive analyses. At the same time it would be very desirable to make a partial examination of a much larger number, in order to obtain a wide basis for the establishment of certain points; as, for instance, the average percentage of clay in different superficial deposits, and tho percentage of clay they contain in an undecomposed form. A fresh supply of circulars is therefore being issued, especially to those districts concerning which there is the greatest deficiency of information, and the results will form the subject of a future report. Explanation op the Method of Analysis employed. A weighed portion of each sample of soil was first exposed to the air in a thin layer for ten days, to free it from accidental water; then subjected to a temperature of 212° P., till the weight remained constant. The loss thus incurred was then tabulated, a knowledge of which affords a very good guide as to the comparative retentive power of the several soils for water. The dried soils were afterwards gently calcined, till all carbonaceous matter was consumed. The loss represented the total quantity of organic matter present, together with a variable quantity of constitutional water belonging to the earthy portion of the soil; a quantity, however, always so small as not materially to affect the correctness of the results arrived at. Another weighed and much larger portion was placed in a well-washed filter, and distilled water passed through unremittingly till everything soluble was removed. The filtrate was evaporated to dryness at 300° P., and the soluble organic matter determined as before by the loss suffered by calcination of the dried residue. The soluble organic matter subtracted from the total of organic matter at first obtained, gives the organic matter insoluble in water (col. 8). The residue from calcination was finally weighed. The analysis of the part soluble in water is not tabulated with the rest, partly because such would tend to encumber and unduly lengthen a table already extended enough, and partly because a complete analysis has frequently been omitted; but, instead of this, a column is reserved for an entry of its general character. The nature and proportion of these salts has, no doubt, a close relation to the amount and nature of such salts which are applicable for immediate assimilation by plants. A small portion of the soil was next digested for two hours with weak hydro-chloric acid of a certain strength, and the quantity of substances dissolved, together with their general nature, ascertained ; but it was only in the more characteristic or type specimens that it was thought necessary to determine the phosphoric acid, or to separate the alkalines, potash, and soda from each other. The ultimate object of this process was the determination of the relative susceptibility of these several soils to common meteoric influences, the acid here employed anticipating, as it were, the disintegrating effect of meteoric water containing air and carbonic acid in solution. The mechanical analysis which followed was effected by washing with water in such a manner that the clayey matter was separated, and the sand and gravel retained for further subdivision and mineralogieal examination, in order to determine the character of the rock mixed with the soil. It was only in a few cases that the greater portion of the coarse-grained material could not be readily identified. This combination of chemical and mechanical with mineralogieal analysis, appears more advantageous than a simply chemical and mechanical one ; as the composition of the soil is determined by it with sufficient exactness in less time, while the partial chemical analysis, which is part of this method, affords an indication of the rapidity with which decomposition progresses in each case, and the nature of the substances which would be thereby eliminated in forms suitable for maintaining plant life. 2. —Mode or Arrangement oe Table. 1. Prom tho most recent discoveries, and deductions therefrom by agricultural chemists, it appears to be highly probable, if not positively certain, that the relative fertility of any soil is in direct proportion to its relative power of absorbing and retaining, in a mechanical form, the chemical substances required by plants.