It has already been shown that the rate of evaporation is greater from a wet than from a dry surface.  It follows, therefore, that the critical time for preventing evaporation is when the soil is wettest.  After the soil is tolerably dry, a very large portion of the soil-moisture has been lost, which possibly might have been saved by earlier cultivation.  The truth of this statement is well shown by experiments conducted by the Utah Station.  In one case on a soil well filled with water, during a three weeks’ period, nearly one half of the total loss occurred the first, while only one fifth fell on the third week.  Of the 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 beneficial, 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 cultivation, 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, unplowed 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 over thoroughly several times if necessary, with an iron tooth harrow, the teeth of which are set to slant backward in order not to tear up the plants.  The loose earth mulch thus formed is very effective in conserving moisture; and the few plants torn up are more than paid for by the increased water supply for the remaining plants.  The wise dry-fanner cultivates his land, whether fallow or cropped, as early as possible in the spring.

Following the first spring plowing, disking, or cultivation, must come more cultivation.  Soon after the spring plowing, the land should be disked and. then harrowed.  Every device should be used to secure the formation of a layer of loose drying soil over the land surface.  The season’s crop will depend largely upon the effectiveness of this spring treatment.

As the season advances, three causes combine to permit the evaporation of soil-moisture.