TIME OF PLOWING SMALL-GRAIN STUBBLE. 7 
water available on them. For example, if one field is found to be 
wet to a depth of \\ feet and a second is wet to a depth of 3 feet it 
may be assumed that the second field has approximately twice as 
much water in it as the first field. In the discussion of soil moisture 
as related to time of plowing it is not necessary to consider the 
hygroscopic moisture, which is not available to the plants. 
Wheat plants at Akron readily root to a depth of 5 feet if the soil is 
wet from the surface to that depth and if there is not a more easily 
obtained supply nearer the surface. This soil will hold an average 
of 1J inches in each of the upper 5 feet, so that 6§ inches of precipi- 
tation may be stored for the use of the crop. This would be suffi- 
cient under favorable wind and temperature conditions to produce a 
crop of 10.7 bushels of wheat per acre. 1 
In order to study the relative efficiency of different times of plow- 
ing in the accumulation of moisture in the soil and the relation of the 
moisture in storage to crop production, moisture determinations 
have been made at more or less regular intervals. 2 A continuous 
record of the moisture content is available for only two plats under 
discussion. These are plats A and B, continuously cropped to 
spring wheat, and are probably representative in their moisture 
relations of all spring-plowed and fall-plowed plats, plat A being con- 
tinuously spring plowed and plat B continuously fall plowed. 
In Table VI are presented the data obtained in making the moisture 
determinations on these plats. The moisture content is shown in 
percentages of the dry weight of the soil. For example, 10 per cent 
means that for every 100 pounds of dry soil there $re 10 pounds of 
water. In the table are shown the total water content at the time 
of sampling, the nonavailable water, or that which can not be utilized 
by the plants, and the water available for the use of the plant. 
The total water content needs little explanation. It is determined 
directly by weighing the sample of soil, drying it thoroughly, reweigh- 
ing, and determining the loss in weight. The difference in weight 
represents the amount of water. 
As water from the soil is used by the crop and the soil becomes 
drier, a point is reached below which the plants can obtain no more 
water. This point is called the " minimum point of exhaustion," and 
the amount of water remaining in the soil below this point is termed 
" nonavailable." The minimum point has been determined by 
observing the behavior of the crop on the plat and by frequent sam- 
pling. By continuing such study through several years the minimum 
point can be determined quite accurately. 
1 See Briggs, L. J., and Shantz, H. L., op. cit. 
2 Moisture determinations are made through the cooperation of the Office of Dry-Land Agriculture and 
the Biophysical Laboratory. 
