s 
BULLETIN 151, U. S. DEPARTMENT OF AGRICULTURE. 
For the most part the curves show only slight variations in the 
amount of moisture present in the fallowed and continuously cropped 
plats during the period when crops were on the land. There was a 
somewhat higher moisture content in the soil of the fallow plats at 
the time when crops were growing on the other plats; but, as already 
stated, the difference generally disappeared by the next planting 
time. 
RUN-OFF FROM FALLOWED PLATS. 
The uniformity in soil-moisture content at planting time, already 
noted, is probably accounted for by the higher loss by run-off from 
fallow plats than from those which were cropped eveiy year. Dur- 
ing the years covered by this report the precipitation during the 
winter and early spring was comparatively heavy. Consequently, 
so far as the rainfall during the winter and spring immediately pre- 
ceding corn and cotton planting was concerned, land cropped each 
year and plowed as soon as possible after the removal of the crop 
had the same opportunity to store moisture as fallowed land had 
during the same period. Even though the fallowed land contained 
a larger amount of moisture at the time of seeding oats in the fall, 
a larger amount of run-off from the fallowed plats during the winter 
would result in approximately uniform moisture conditions in all 
the plats at the time of planting corn and cotton the following 
spring. That there is a difference in the run-off from the different 
plats is proved by the results of determinations shown in Table II. 
On February 16, 1912, three days after a rain of 3.3 inches, soil 
samples were taken on one plat of oats and on five fallow plats where 
the length of time since plowing varied from 3 to 18 months. Table 
II shows the moisture content at the last sampling before the rain and 
again three days after the rain, together with the increase in moisture, 
the run-off in inches, and the percentage of rainfall lost by run-off. 
On February 26, samples were again taken on the same plats after 
a 2-days' rain of 2.9 inches. The results are also given in Table II. 
Table II.- 
-Absorption and run-off from rains in February, 1912, San 
ment Farm. 
Antonio Experi- 
Fallow period 
or crop. 
Samples taken on Feb. 16, three days after a 3.3-inch rain. 
Plat Xo. 
Average moisture 
content in 3 feet. 
Increase. 
Run-off. 
5 days 3 days 
before after 
rain. ' rain. 
Per cent. 
Inches. 
Inches. 
Percent- 
age of 
rainfall. 
A4-1 
3 months 
Percent. Percent. 
15. 8 19. 9 
19.1 ; 21.6 
17. 2 19. 8 
20.0 23.0 
18.4 , 20.6 
4.1 
2.5 
2.6 
3.0 
1.92 
1.17 
1.22 
1.40 
1.38 
2.13 
2.08 
1.90 
2.27 
1.34 
41.8 
A4-2 
15 months 
64.5 
A4-3. . . . 
5 months.. 
63.0 
A4-4 
18 months. 
57.5 
A4-5 
6 months 
2.2 1 1.03 
68.8 
A4-6 
Oats 
18.1 22.3 4.2 1.96 
40.6 
