Tue Carson Dioxipe oF THE Sort AIR 331 
that in the uncropped soil after the removal of the crop, reported by 
these investigators, may not be due to interference with bacterial activities, 
since in the work reported in the present paper no such action on the soil 
organisms, as evidenced by a decrease in carbon-dioxide production, was 
observed. It may be possible that the decrease noted by Bizzell and 
Lyon was due to some other effect of the crop, such as, for example, the 
reduction of the soil moisture. It has been pointed out in the review 
of the literature of the subject that some investigators have noted a 
decrease in carbon dioxide where the moisture was reduced below a certain 
optimum amount. On referring to figure 46 it will be seen that early in 
July, 1917, the carbon dioxide in the cropped soil showed a marked 
decrease. This was due to the drying-out of the soil when, thru an over- 
sight, it was not watered for two days. - 
It has been pointed out that the carbon dioxide in the cropped soil 
was somewhat higher (about 30 per cent) in 1918 than it was in 1917. 
The results for the two seasons are not strictly comparable, because in 
1917 the crop was sown in April whereas in 1918 the seeding was made 
in January. Also, in 1917 the number of plants was reduced to fourteen 
in each pot, while in 1918 there were fifteen. However, the total dry 
weight of the mature crop from the four cans in 1917 was 494.5 grams, 
as against 416 grams in 1918. 
Carbon-dioxide and water relationships 
As has already been stated, a record was kept of the amount of water 
added to the cropped cans in order to maintain them at a moisture content 
of 30 per cent (oven-dry basis). The sand mulch on the soil, as has been 
pointed out also, was so effective that the loss in moisture on the cropped 
cans could be regarded as due entirely to transpiration. 
The total amount of water lost on the cropped cans each week was 
determined in 1917 and 1918 for a period of ten weeks during which the 
crop was making the most active growth. These amounts, together with 
the average weekly content of carbon dioxide in the cropped and the 
uncropped soil, are indicated in tables 3 and 4 (appendix, pages 357 to 
358), columns A, C,and E. The difference between the carbon dioxide in 
the cropped and that in the uncropped soil is givenin column F of the 
same tables. The carbon dioxide produced to each pound of water used 
is shown in columns G and H. The figures in column G were obtained 
