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 1J 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 are 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 lias 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. 



' See Brlggs, L. J., and Bhantz, E. L., op. elt. 



a ICoktan determination i an made throagJb the cooperation <>f the Office ol Dry-Lund Agriculture and 

 the Blopbj ileal Laboratory. 



