Z BULLETIN 253, U. S. DEPARTMENT OF AGRICULTURE. 
,the most necessary of the cultural operations, but this is not sub- 
stantiated either by the experience of many successful farmers or 
by the records from experimental work. A smooth, deeply plowed, 
well-harrowed surface looks well and gives the impression of care- 
fully conducted farm operations, but may prove detrimental in crop 
production. The smooth, finely pulverized surface is readily sub- 
jected to blowing, and the loose, unpacked seed bed may be quickly 
dried by the rather free circulation of air through it. Stubble left 
on a field may give it an unkempt appearance, but at the same time 
may be of value in catching snow or in preventing the soil from 
blowing. There may be a great deal of misdirected labor expended 
in preparing a seed bed, which defeats the object sought rather than 
aids in the production of a crop. 
Moisture is generally considered the most important factor in crop 
production in eastern Colorado. Its conservation is the primary 
object in cultivation. Experience has shown that on this soil weeds 
are the greatest robbers of moisture, and their control must always 
be considered. Stubble, weeds, and uneven ground are the common 
means of retaining snow and holding a large part of the winter pre- 
cipitation. In deciding when a field shall be plowed, the question 
whether a greater amount of moisture will be accumulated by hold- 
ing the snow that falls than will be dissipated by the growth of weeds 
must be paramount. It can best be decided by the man on the 
ground. In answering this question several factors must be consid- 
ered, namely, the amount of moisture already in the soil that may 
be lost through weed growth, the probable time before the weeds 
vail be killed by frost, the possibilities of increasing the water in 
storage in the soil by holding the snow that may come, the danger 
of soil blowing if the stubble and weeds are removed, and the distri- 
bution of the farm labor. 
In the following pages the importance of these factors will be 
considered and the experimental evidence bearing upon them will be 
given. It is believed that a careful consideration of these data will 
assist the farmer in determining the best time to plow. 
In order to interpret properly the following data it is necessary to 
consider the amount and distribution of precipitation during the 
time these investigations have been in progress. The precipitation 
records and crop yields of the six years from 1909 to 1914, inclusive, 
should be studied together if any correlation is to be seen between 
the distribution of precipitation and the time of plowing. 
PRECIPITATION. 
Table I gives the monthly precipitation for 10 years from 1905 to 
1914, inclusive, which is the period covered by continuously recorded 
observations at Akron, Colo., both bv the United States Weather 
