76 QUEENSLAND AGRICULTURAL JOURNAL. [1 Fexn., 1902. 
classes of soils which I shall not tell you about, because in Australia there is sO | 
much good, rich land that the farmers never cultivate them. These are peat | 
soils and marl lands. There are in most countries swampy tracts of land, the | 
soil of which is composed almost entirely of organic matter (or peat), such aS | 
the matted roots of plants which have long ago disappeared. Now, a soil which | 
contains too much of any one constituent is always poor, and it requires many | 
things to be done to it to bring it up to fertility. 
Maru contains a quantity of lime and clay, and is called ‘“ caleareous | 
clay” from the Latin word calz, limestone. The principal use of marl is for | 
mixing with very light soils, to make them hold together better, and thus 
enable them to obtain moisture, which they would not do unless the stiff, clayey | 
marl were added to them. ik 
However, as we do not meet with many such lands in Australia, we need Es 
not discuss them here, but will pass on to the subject of manure. ; 
Manure (from the French word ‘“ manwuvrer,” to work by hand), in the | 
old days of farming, was always understood to mean the dung (from the ~ 
German word Diinger) and straw bedding from the stables or the farmyard, — 
and hence it is also called farmyard manure. But now the word is applied to 
many other substances which are spread on the land to increase the fertility of | 
the soil. 
Now, this subject of manures requires that you should have a more | 
advanced knowledge of the requirements of plants than you have gained up to — 
the present. Most crop plants have been carefully examined—aNnatyseED is the 
term used, you remember—by agricultural chemists, in order to find out what — 
they are composed of, and these chemists are able to tell us exactly the elements — 
and the quantities of them which any plant contains, and so enable the farmer — 
to supply just the kind of plant food which is required for his crops. 
Plants are made up of organic matter which will burn, and water. They | 
also contain inorganic or mineral matter which will not burn. The former are — 
said to be COMBUSTIBLE, the latter to be rncomBustiBLE. These latter appear | 
as ashes when a plant has been burnt. Now, let us see what the organic | 
portions of the plant are composed of. They are the elements carBoN, — 
NITROGEN, HYDROGEN, and oxyaEN. The inorganic parts are made up of a 
great many more substances. They are principally minerals, such as LIME, | 
MAGNESIA, POTASH, SODA, OXIDE OF IRON, SILICA, and CHLORINE, besides which | 
we find PHOSPHORIC ACID and SULPHURIC acrD present in them. : 
You do not, at this stage, require to be reminded that carbonic acid in the — 
air is absorbed by the leaves of the plants, and that the oxygen absorbed with | 
it is separated from the carbonic acid and given out again, and that, by means — 
of the roots, certain constituents, such as nitrogen, phosphoric acid, and potash, — 
are supplied to the plant from the soil. Now, you can easily understand that 
if you gather no crops, but allow the natural growth to die off and decay, the 
elements which went to building up that natural plant growth are returned to 
the soil and to the air, and nothing has been removed. But, when the farmer 
begins to cultivate the soil and to carry off large crops, you must see that in | 
those crops he takes away a certain quantity of plant food from the soil which 
is not returned toit naturally. When this occurs, the most fertile soils will — 
gradually lose their fertility, because of the removal of the nitrogen, potash, — 
and phosphoric acid, which have been taken out of them to produce the cro 
the farmer has removed. It is just the same as it I had a pocketful o 
money, and kept on parting with some of it. If I did not put more into my | 
pocket, I should, at last, be left with nothings Or take another illustration. — 
BUpnoee you make a billyful of tea. At first the tea is good and strong, but | 
you keeping on drinking it, and to make it supply your wants you add water 
to it, just as you give water to a plant; but if you keep on adding only — 
water your tea gradually gets weaker, until at last you have nothing but hot 
water left. If you wanted your tea to keep up its strength, you should have 
