240 QUEENSLAND AGRICULTURAL JOURNAL. [1 Ocr., 1962. 
Let us first consider the amount needed for a single watering. This must 
be determined by the amount of water the soil contains at the time it is to be 
irrigated, and by the amount it should contain in order that plants may do their 
work to the best advantage. 
The maximum capacity of upland field soils for water ranges from about 
18 per cent. of their dry weight for the light sandy types to about 30 per cent. 
for the heavy clayey varieties, while the amounts of water these soils should 
contain in order that plants may thrive in them best is from 12 to 14 per cent. 
for the former and from 18 to 20 per cent. for the latter. The growth of 
plants will be seriously checked in sandy soils when the water content falls 
below 8 per cent., and in heavy, clayey types when it falls below 14 per cent. 
of the dry weight of the soil. 
The dry weight of a light sandy soil and subsoil will average about 105 Ib. 
per cubic foot, and the heavy, clayey type about 80 lb. per cubic foot. Hence 
the maximum amount of water per cubic foot of soil would be about 24 lb. for 
the clay and 18°9 lb. for the sand. This being true, 4°6 inches of water on the 
level would completely saturate the surface foot of heavy clay soil, were it 
entirely dry to begin with, while 3°6 inches would place the sandy soil in a 
similar condition. 
But since water should be applied as soon as the water content of the 
sandy soil falls to 8 per cent. and that of the clayey soil to 14 per cent, it 
follows that under these conditions 10°5 lb. of water, or 2 inches, is the maximum 
amount which would be needed to fili the surface foot of sandy soil and 12°8 
Ib., or 2°46 inches, is enough to fill the surface foot of clay soil. 
If we consider the second foot of soil to have been dried out to a 
corresponding extent, and that it is desirable to saturate this with water also, 
then the amounts just stated would need to be doubled, 4 inches being 
demanded for the sandy soil and 4°92 inches for the clayey soil. It is quite 
certain, however, that such an application of water to a field at one time would 
result in the percolation of a considerable amount of this water below the 
depth of root action, and hence in a considerable loss of it unless a large crop 
were growing upon the land at the time. It appears, therefore, that the 
amounts of water which may be applied to a field at one time will lie between 
2 and 5 inches in depth over its whole surface. 
How often this watering may need to be repeated, it is not possible to 
state in anything like definite terms, but practical experience shows that as a 
rough average the intervals between watering where maximum yields are sought 
can not much exceed seven to fourteen days, the time being shortest when the 
crop is making its most vigorous growth. ; 
In experiments at the Wisconsin Station during 1895, corn was irrigated 
once about every seven to nine days, applying at each time 4°43 inches of water. 
The corn, however, was planted very thickly upon the ground, the rows being 
only 30 inches apart and the hills 15 inches apart in the row, with from two to 
five stalks in each hill. The first irrigation was given 26th June and the last 
15th August, the total amount of water applied being 26°6 inches. The yield 
produced was 11,125 lb. of water-free substance per acre. 
In the case of the water meadows of Europe very little attention is paid 
to the natural rainfall, the irrigation waters being applied whenever it is 
possible to do so, and whatever rains fall are counted as so much additional 
gain. It is true, however, that on most lands with crops other than grass, 
attention would have to be given to the natural rainfall in the application of 
water by irrigation, but oversaturation of the soil and a positive waste of water 
should occur. 
If it is regarded that ample irrigation has been provided when 2 inches of 
water is supplied every ten days as a minimum, and 4 inches as a maximum, 
then, to meet this demand, there would be required for one acre a continuous 
flow of water at the rate of 0°5042 cubic foot, or 3°77 gallons per minute for 
