The Storage and Use of Soil Moisture 
63 
corn in 1908. At the sampling about June 20, the moisture con- 
tent of the first three feet is above carrying capacity. This 
sampling was done so soon after a rain that the moisture had 
not had time to move downward. The first sampling in July 
shows that this moisture had moved into the lower depths, as 
indicated by the abrupt rise in the curves in the fifth and sixth 
foot-sections. After July 20 the crop not only uses the light 
rains that come but uses the available water from the first four 
feet of soil. The use of the water from the first three feet of 
soil is rather gradual and simultaneous. From the fourth foot 
it is abrupt. The first four feet are dried to about 10 per cent. 
The fifth and sixth feet contain 15 per cent at harvest, showing 
that the roots feed to at least four feet. 
The data in Table 28 were obtained from frequent sampling 
made on a plat summer tilled 1912 and growing spring wheat 
1913. It was hoped to show more clearly how the moisture is 
used from the soil. At the first sampling the first and second 
feet are taken in foot-sections. Thereafter they are divided into 
six-inch sections. The table shows the soil practically filled with 
water at the first sampling. Very little water is used the first 
month. Kains occasionally replenish the water near the surface. 
On June 23 the third foot was practically dry and on July 8 
the fourth foot was dry. Some water is lost from the fifth and 
sixth foot-sections but the abrupt break in water content comes 
between the fourth and fifth foot-sections. 
In Chart VIII is shown the use of the soil water by spring 
wheat. In each case the crop was on summer tilled land. Only 
the water available to the crop, or that above 8 per cent, is rep- 
resented. The depth is indicated on the left of the chart. The 
dates shown indicate when the samples were taken. Each small 
vertical space represents 5 per cent of available water. 
The chart shows that under the favorable rainfall conditions 
the crop did not reduce the water content of the soil until after 
the June samples were taken. There was enough rainfall to 
replace any water that was used. In 1909 the July sampling 
showed the water used from the first and second foot had been 
replaced with water from a recent rain. 
In 1908 the crop was seeded April 4 and harvested August 3. 
The yield was 10.5 bushels an acre. In 1909 the seeding was done 
April 12. The crop was harvested July 29 and yielded eighteen 
bushels an acre. The crop this year was injured by a freeze in 
April. The chart further proves that spring wheat feeds to a 
depth of four feet. In each case it used practically all the avail- 
