28 
Research Bulletin No. 5 
Chart III gives further data concerning the effects of summer 
tilling. On the right hand side of the chart beginning at the 
top are shown first the spaces showing rainfall in inches, and 
rainfall for the year. Below that are shown the depth which 
each section of the chart represents, from one to six feet. On the 
left of the chart is shown the per cent of water. Each section 
of the chart is divided by minor lines. The spaces between these 
lines represent five per cent of water in the soil. The heavy, 
broken horizontal lines represent the "wilting coefficient'' as 
defined by Briggs and Shantz.* The wilting point as indicated 
on these charts is probably somewhat high as is shown by field 
results. All water over 8 per cent is available for crop use 
in this soil. The chart is divided to show the different months 
and days of the month. The perpendicular lines near the top 
represent the amounts of various rains on various dates. The 
total for the month is shown in figures at the top of that section. 
The heavy, solid, horizontally-drawn lines represent the moisture 
content of the soil at that particular depth. (This explanation 
will serve for all charts of this kind used in this bulletin.) 
It will be noted from the chart that at the first sampling the 
first foot of soil was filled with water and some water was avail- 
able in the second foot. Below that the soil was dry. The chart 
shows several heavy rains between the sampling in June and 
that done in July. The June sampling showed that the third 
foot was beginning to receive water and that the fourth foot 
had not yet received any water. In July the sampling was done 
so soon after the heavy rain that the first three feet had more 
water than they would hold. Water had penetrated to five feet. 
At the time of the first sampling in August, the first six feet were 
filled to the maximum carrying capacity. Some loss is shown 
during the latter part of the season, which was very dry. 
Chart IV shows the effect of summer tilling during a less 
favorable year (1911) than shown in Chart III. The samplings 
this year are not frequent enough to show all the fluctuation in 
the moisture content of the first foot. The chart does show, tho, 
the ultimate results. There were two rains of more than one 
inch during the season. The effect of the first one is seen at the 
second sampling. All the water that was held is still in the 
first foot. At the next sampling an increase of water is shown 
in the second foot. The third foot does not show any increase in 
* Bulletin No. 230 of the Bureau of Plant Industry, U. S. Dept. of Agr., 
on "The Wilting Coefficient for Different Plants and Its Indirect Deter- 
mination," by Briggs and Shantz. 
