REGULATING THE EVAPORATION 159 
amount lost during the first week, over 60 per cent 
occurred during the first three days. Cultivation 
should, therefore, be practiced as soon as possible 
after conditions favorable for evaporation have been 
established. This means, first, that in early spring, 
just as soon as the land is dry enough to be worked 
without causing puddling, the soil should be deeply 
and thoroughly stirred. Spring plowing, done as 
early as possible, is an excellent practice for forming 
a mulch against evaporation. Even when the land 
has been fall-plowed, spring plowing is very bene- 
ficial, though on fall-plowed land the disk harrow is 
usually used in early spring, and if it is set at rather a 
sharp angle, and properly weighted, so that it cuts 
deeply into the ground, it is practically as effective 
as spring plowing. The chief danger to the dry- 
farmer is that he will permit the early spring days 
to slip by until, when at last he begins spring culti- 
vation, a large portion of the stored soil-water has 
been evaporated. It may be said that deep fall 
plowing, by permitting the moisture to sink quickly 
into the lower layers of soil, makes it possible to get 
upon the ground earlier in the spring. In fact, un- 
plowed land cannot be cultivated as early as that 
which has gone through the winter in a plowed 
condition. 
If the land carries a fall-sown crop, early spring 
cultivation is doubly important. As soon as the 
plants are well up in spring the land should be gone 
