1 Seer., 1897.] QUEENSLAND AGRICULTURAL JOURNAL. 228 
smallest size that should be used under any conditions, and where the drains 
are of any length, say over 100 yards, before being connected with the main 
drain or outlet, the size of the lower tiles should be increased to at least 3 
inches. For main drains, tiles of 4, 6, or 8 inches diameter are used, the size of 
the tiles depending on the extent of the ground to be drained. ‘Tiles of larger 
size than this are not required except in very extensive drainage operations. 
Where a large area of land is to be drained in any one district it will be found 
to be much cheaper to make the tiles on the land to be drained, if there is any 
suitable clay available, as a pug-mill and tile-making plant do not run into a 
yery great amount, whereas the cartage and freight on drain tiles obtained 
from a distance soon become a heavy item when there is a considerable 
quantity of draining to be done. 
Liffects of Drainage.—The effects of drainage may be briefly summarisetl 
as follows :— 
J. Drainage removes the superfluous moisture from the soil, and facil#* 
tates cultivation, so that drained land can be worked sooner after 
rain than undrained land. 
2, Drainage removes stagnant water, and prevents the accumulation of 
same round the roots of fruit trees or plants, so that the roots are 
able to develop healthily. 
3. Drainage increases the absorptive properties of the soil, so that 
drained soils retain moisture better during a prolonged dry spell than 
undrained soils. ; 
4, Drainage warms the soil, as undrained land is always colder than 
drained land, owing to the excessive surface evaporation from such 
soils, such evaporation cooling the land. Undrained soils always 
freeze sooner than drained soils, undrained land being sometimes 
white with hoar frost, when drained land adjoining is practically 
free from frost. 
Cu 
. Drainage ewrates the soil, as the space occupied by water before 
drainage is occupied by air afterwards, and this air in the soil acts 
directly in disintegrating the soil and consequently in liberating 
plant food for the use of the trees or plants growing in the soil ; 
a thorough eration of the soil is also essential to the healthy deyelop- 
ment of all plant growth, as, unless the roots are supplied with 
plenty of air, the plants are never healthy or vigorous. 
G6. Drainage renders the land more friable, and consequently less expensive 
to work. 
7. Drained land responds to the application of manure much more 
readily than undrained land, and the results of the manuring are more 
apparent. In the case of very soluble manures, however, a large 
quantity of manurial matter is apt to be carried off by the drains 
after heavy rains, so that such manures should not be applied in 
large quantities at any one time to well-drained soils, but should 
be applied in small quantities, when the plants or trees actually 
require them—that is to say, during a period of active plant growth. 
In drainage there are several points that are worthy of especial mention, 
and which should always be carefully attended to :— 
1. Whatever drainage has to be done, see that it is well done, as bad 
drainage is often worse than no drains at all. 
2. See that the tiles are well laid, and the drain has a regular fall. 
7 
