On Irrigation in Tasmania. 
91 
300,000/. per annum. Nor is it at all too much to sup¬ 
pose that, some years hence, when the lands are more 
extensively cultivated, irrigation may be carried to such 
an extent as to make an increase of produce to the value 
of several millions per annum. 
It may here be observed, that in the only instance which 
came to my knowledge of the water being let out on the 
natural pasture, the effect appeared to be very insigni¬ 
ficant ; the principal part of the advantage being lost 
where the land had not previously been broken up. 
Before proceeding to consider by what methods the 
irrigation of land in this Colony may best be accom¬ 
plished, it will be well to examine what quantity of water 
will be required per acre. In India, in nearly the hottest 
season, when the land is not shaded by the crop, the 
extreme quantity required to keep the land Hooded to the 
depth of several inches is found to be about 70 cubic 
yards per acre per day; but towards the end of the 
season, when the weather is cool, and the land shaded by 
the crop, about 24 cubic yards is ample. In this Colony, 
therefore, allowing for the difference of temperature, and 
for the circumstance of its being necessary merely to keep 
the ground sodden, but not Hooded, about 16 cubic yards 
will probably be found sufficient: this is equal to a fall of 
rain of rather more than 1 inch (which is a good night’s 
rain) once in ten days. At this rate an acre of grass 
land would require during the whole summer, viz. from 
1st November to 1st April, or five months, 2400 cubic 
yards; and an acre of grain, from 1st November to 
1st January, 1000 cubic yards. In irrigating grain it is 
of the greatest consequence that it should be well supplied 
from the time of flowering till the corn begins to turn 
colour: if the supply is scanty at this time, although the 
crop may be luxuriant, it will not yield well. Hence we 
conclude, that an acre of reservoir or tank, covered to* 
