2 BULLETIN 1257, U. S. DEPARTMENT OF AGRICULTURE 
In this discussion " reclamation "' is used in the popular sense, as 
applying only to the preparing of wet and overflowed land and of 
dry land, for use for agriculture. 
The 1921 Yearbook of the United States Department of Agri- 
culture gives the areas of such lands, as follows : 
ReclaimaJ)le areas in the United States, 1921. 
Acres. 
Irrigable land not now irrigated 30, 000, 000 
Wet land requiring drainage only 30, 00O, 000 
Wet land requiring drainage and clearing 60, 000, 000 
Total 2 120, 000, 000 
The estimate of the area of land that can be reclaimed by irri- 
gation is based on estimates of the water supply within the regions 
where irrigation is necessary to the growing of crops or practicable 
as a means of increasing or insuring crop yields. A large part of 
the land reported as pasture and range land, and of that reported 
as desert, is susceptible of irrigation so far as its topography and 
the inherent qualities of the soil are concerned, but it is not within 
reach of any known water supply. The estimated total of the area 
that can be irrigated is based upon estimates of the total quantity 
of water available and of the quantity of water used per acre. 
Studies made by this department and the State experiment stations 
show that the quantities of water used in common practice are far 
in excess of the water requirements of crops, indicating that it is 
possible to reduce greatly the quantity of water used per acre, and 
thus increase the total area that can be supplied with water. These 
studies show also that the law of diminishing returns applies to the 
use of water in irrigation with peculiar force. That is, when in- 
creasing quantities of water are applied to a field the increase in 
crop is much less than proportional to the increase in the quantity 
of water. In fact, the point of actual decrease in yield is soon 
reached. This means that a given quantity of water will produce 
more crop when applied to a large area than when applied to a small 
area. As demand for crops increases, the tendency is to use less water 
per acre, and to irrigate larger areas. It seems likely, therefore, that 
the area ultimately irrigated will be considerably larger than that 
given in the 1921 Yearbook. 
The estimate of the area that can be reclaimed by drainage is 
based on more or less accurate measurement and estimates of the 
area of the land itself, rather than on estimates of other indetermi- 
nate factors, as is the case with irrigation. It is probable that this 
figure is much more accurate than that given for irrigation. 
It appears, therefore, that it is possible to increase our present 
improved area about 25 per cent by reclaiming wet and dry land. 
This will not represent an absolute increase of 25 per cent in our 
agricultural production, since most of the land concerned now pro- 
duces something, chiefly grasses and timber. The irrigation of the 
arid lands will replace a \ c y extensive type of grazing with a very 
high type of crop production. Measured by the carrying capacity 
for animals, it is probable that the productivity will be increased 
at least a hundredfold. The untimbered wet lands produce in their 
s Yearbook 1021, p. 430. 
