4 BULLETIN 157, U. S. DEPARTMENT OF AGRICULTURE. 
with snow. When there is no snow, however, winterkilling of fall- 
sown cereals is not uncommon. 
Only two months of the year, July and August, have been free 
from frost. Normally, however, there are from 90 to 100 days in the 
frost-free period, extending from June 15 to September 15. 
EXPERIMENTAL WORK. 
All experiments were conducted under field conditions, the treat- 
ment differing from common farm practice only in the tillage method 
under test. 
DESCRIPTION OF PLATS. 
Rectangular tenth-acre plats were used for all experiments except 
one, in which fifth-acre plats were used. The tenth-acre plats were 
36 by 121 feet, while the fifth-acre plats were 72 by 121 feet. The 
plats lay in series running north and south. The series were in pairs, 
the two in each pair being separated from each other by a 5-foot alley, 
while between the pairs of series there were roads 13 feet wide. The 
plats within each series were separated by 5-foot alleys. Thus, each 
plat was separated from the others by a 5-foot alley on two sides and 
one end and by a 13-foot road on the other end. 
Two sets of plats were used for each experiment, except in the case 
of the continuous-cropping test. These two sets of plats permitted 
the alternate cropping and fallowing of each plat, a practice which was 
followed regularly. 
SOIL-MOISTURE DATA. 
Soil-moisture data were collected on most fallow plats and on 
some cropped plats. The number of samples taken varied with the 
plan of the experiment. Soil tubes were used in sampling, the soil 
being taken out in foot sections to depths of 6 to 10 feet. Each foot 
section was placed in a soil can, which was immediately covered 
with a close-fitting lid and taken soon after to the laboratory. From 
two to four cores were taken from each plat on each day that it was 
sampled. 
The moist weight of each sample was obtained soon after its 
arrival in the laboratory. In no case was the weighing delayed 
more than half a day, the sampling usually being done in the fore- 
noon and the weighing in the afternoon. After the moist weights 
were obtained, the samples were placed in an asbestos-board oven, 
where they were subjected to an average temperature of 110° C. 
They were left in the oven until constant weight was reached and 
then the dry weight of each sample was determined. The difference 
between the moist and the dry weights of the sample was then 
divided by the dry weight of the sample, to get the percentage of 
moisture. An average of the moisture content of all samples taken 
on a plat was considered the average moisture content of the plat. 
