20 Bulletin 1356, U. S. Department of Agriculture 
enough to cover the land under cultivation to a depth of 6 or 8 inches 
for at least 90 days and must be available during May, June, July, 
August, and September. During normal seasons the precipitation 
and the water from streams and deep wells in this area are adequate 
to supply irrigation for approximately a million acres. Dry seasons, 
however, reduce this total and limit the rice crop to a much smaller 
acreage. 
In a section where there is abundant rainfall an extravagant use 
of water is to be expected and probably will be very difficult to pre- 
vent. The delivery of irrigation water for rice in southwestern 
Louisiana has ceased to be a problem. It has been so satisfactorily 
solved that if the payment for water could be based upon volume 
used instead of some form of crop rental the rice farmers of this 
section could probably compete with any rice area in the world. A 
cash rental, however, can not be put in practice until the farmers 
become impressed with the importance of conserving water. 
The depth and character of the soil, imperviousness of the subsoil, 
compactness of levees, depth of submergence, and the length of the 
growing season are the factors that determine the quantity of water 
which must be supplied to a field of rice to obtain profitable produc- 
tion. Shallow clay soils are best adapted to rice culture. They 
require less water to maintain a given depth of submergence and 
lose less water by seepage than soils lighter in texture. On account 
of the abundance of water in southwestern Louisiana many soils 
of lighter type are used for rice; but if the water supply should 
ever be diminished the crop would ultimately be confined to the 
shallow clay types with impervious subsoils, because of the smaller 
quantity of water required for their irrigation. Clay soils also are 
useful in constructing water-tight levees, an important consideration 
in conserving irrigation water. If the outside levees are broad and 
firmly constructed of a compact clay soil, seepage may become a 
negligible factor. Levees should be permanent and constructed on 
contour lines at distances which will hold the water at an average 
depth of 6 to 8 inches. Their efficiency in controlling the field water 
depends largely upon their structure. They should be at least 12 
feet wide at the base and built with broadly sloping sides to a 
height just sufficient to prevent the water from overflowing into 
the fields below. Levees of this construction are practically sub- 
merged during the irrigation period. There is no seepage through 
them after they have become saturated and thoroughly settled. On 
account of their height, they also can be brought under cultivation 
and sown to rice, preventing a waste of land and leaving no unculti- 
vated strips for the growth of weeds. 
i The general practice is to seed the crop early and to supply irriga- 
tion water approximately 10 days after emergence. The depth of 
the water at the time of submergence and at subsequent applications 
often varies greatly even under the same management. The time 
of applying irrigation water and the depth of submergence are 
factors which should be more carefully considered, since they deter- 
mine the quantity of water used and also have an effect on vield. 
The irrigation experiments at the Rice Experiment Station were 
conducted on plats 1 square rod in size. The plats were arranged 
side by side in one series. Each plat was completely inclosed^bv 
high levees. Low levees, which are preferable, would have required 
