LECTURE ON AGRICULTURE.

Waikato Times, Volume XXXIII, Issue 2720, 17 December 1889, Page 2

LECTURE ON AGRICULTURE.

The following is a continuation of Mr Dick's lecture delivered by him before the Waikato Farmers' Club at Cambridge on Monday December 2nd : — The inorganic part of the plant consists of phosphorus, Bulphur, chlorine, silicon, iron, calcium, magnesium, sodium, potassium, and manganese. Phosphorous occurs in tho state of phosphoric acid combined chiefly with lime and magnesia, and is a constant constituent of all plants used as animal tood. In combination with lime it forms the chief mineral constituent of animal bones. Phosphorus itself is, as most of you are aware, a pale yellow waxy substance, distinguished by its great inflammability, from which property it derives its name, which literally means light bearer, or light giver. Phosphoric acid which is simply a chemical combination of phosphorus with oxygen has one peculiar property, it can combine with bases to form three different salts. Thus in combining with lime tho one equivalent of phosphoric acid can unite with one, two, or three equivalents of lime, tho resulting salts being known as, monocalcic, dicalcic, and tricalcic phosphate. Sulphur is sufficiently familiar to you ail to require but little description from me. In plants it exists as sulphuric acid combined with bases, and also in a form somewhat difficult to describe, but which very much resembles the white of an egg. Chlorine is a very peculiar gaseous body, it is about 2k time 3as heavy as air, is of a greenish yellow colour, and has a peculiarly suffocating odour. In plants it exists chiefly as chloride of sodium the well known common salt. Silicon does not exist in nature uncombined, but its oxide silica is very abundant both as silica, such as rock crystal or white sand, aud in combination as silicate of various bases, such

as sdicateof alumina the chief constituent of clay. Iron is another substance which ent'.rs into the composition of plants, though it is present only in very small proportion is as oxide of iron. Calcium is a substance known through its oxide lime. Calcium is itself a metal somewhat resembling what is known as German silver. Its oxide, lime, in various combinations as phosphate, sulphate, silicate, etc., enters largely into the compositions of most plants. Magnesium is one mf the same chemical group (the alkaline earths) as calcium, which, in many respects, it much resembles. Sodium and potassium, or rather, their oxides, soda and potash, are known as the fixed alkalies (ammonia in contradistinction being called the volatile alkali), and are very important elements of plant growth, potash especially so. The chief source of supply of potash formerly was from the ashes of trees and plants, but now there are large deposits being worked in Germany where the potash occurs as sulphate or as chloride in combination with other salts, forming substances known askainit, carnallite, etc. Munganese exists ill very small proportion in the ashes of a few plants, but for our present purpose it has no importance, and it is still an open question whether is is absolutely essentiaLto the growth of any plant. The elements I have named are present in varying proportions in various plants, aud in varying proportions in different parts of the same plant. They are also found in different proportions in different stages of the growth of the same plant. Taking wheat, for example, we find the following to be an average analysis uf the ash of its various parts

Roots .Straw Grain J'hosphoric acid 1.70 p.c. 'J liO p.c. 46'00 p.c. Lime oS3 ~ UOO „ I 111 „ Magnesia 1 !*' ~ ~ IH'77 ~ Potash '-"S7 ~ l-> IS ~ 3-'6O ~ Then again, as showing the difference at various stages of growth, Bretschnider (a German investigator), found that the oat plant 58 days after sowing contained S's7 per cent, of ash, when in full bloom .r!)0 per cent., at commencement of ripening 0'33 per cent., and when fully ripe f>MO per cent, of ash, showing that the proportion of mineral matter decreases as the process of growth advances. I ask your special attention to this point, as I may have to refer it again when speaking of soluble and insoluble manures. I may here, for the benetit of grazing members, state that the same remark holds true of flesh-forming constituents as of mineral. With grass Way found that on April 30th it contaioed of (lesli-forming 25'!) per cent., and of fatforming G's per cent. Oil June 2(ith the flesh-formers had sunk to 10'!) per cent, and the fat-formers to 2'l per cent. With vetclus found flesh-forming compounds on May 23rd to be 2S\S per cent. ; on June 12ih, l!l'7, and on July 12 only 15'!) per cent. With red clover, Dr. KmirWoltf found flesh-forming compounds in young clover to he 21.''J per cent, on June 13th, lo'ti per cent., and on July 20th only !l's per cent. 1 have no doubt that many of you are, as most of you are, interested in grazing will find these figures interesting and instructive. We have now seen what elements are required for plant growth, and we will now (following chiefly the inorganic pare which is catered for in manures) endeavour to see how plants are supplied with all they need. Of course tho primary and most obiious reply is from the soil. But as supplying these wants takes fr Jin the soil a certain amount of its wealth, and as tho total amount of that wealth however great is limited, it follows that the soil must in some way bo recouped for its generosity, or a time must come when it will be reduced beyond the po.ver of giving. Soils, like individuals, cannot atford to live beyond their income. We will, therefore, lirst examine the soil to ascertain the total amount of its wealth, and then consider the means by which we may repay its liberality, which means, we call manures, T'irst then, what is soil? This is in itself a sufficient subject for more than one such paper as this. It is but a very meagre answer to the question to siy that soil is the earthy matter in which plants grow. Soils are like individuals in more than tho point already mentioned. Soils liavo character, soi's have temper, soils have disposition, soils have wealth, and soils have a history. Far back through the ages long ore the period which man calls historic, the element* of our snils, took part in wars and revolutions, and in calm and more peaceful changes of the terrific grandeur of which we have but a faint conception. But our present inquiry is as to what they are, not what they have him. Chemically considered soils consist of two parts the organic and inorganic. Tho organic part is derived from decayed vegetable matter, and from the dung and remains of animals and insects. This organic matter besides contributing its share in nitrogenous and carbonaceous compounds to the fertility of the soil is useful in various other ways. It helps to give freedom or friability to the soil, it increases its power of absorbing moisture and gaseous matter, and of holding them when absorbed; it is one of the means by which plant food is retained in the soil, and in its decay it generates some of the agents by which plant food is prepared or rendered available for the uso of the plant. The inorganic or mineral portion of the soil is formed by the disintegration and decomposition of various rocks, and tho composition of soils is as varied as that of the rocks from which they aro derived. The elements present aro chiefly identical with those constituting the inorganic parts of plants though the forms in which these elements are present as well as their relative proportions are widely varied. (To be continued.)