the popular notion to the contrary, and makes the soil more porous, and, therefore, more effectively worked for the prevention of evaporation.  When this practice is continued for considerable periods, the topsoil becomes rich in organic matter, which assists in retarding evaporation, besides increasing the fertility of the land.  When straw cannot be fed to advantage, as is yet the case on many of the western dry-farms, it would be better to scatter it over the land than to burn it, as is often done.  Anything that covers the ground or loosens the topsoil prevents in a measure the evaporation of the water stored in lower soil depths for the use of crops.

Depth of cultivation

The all-important practice for the dry-farmer who is entering upon the growing season is cultivation.  The soil must be covered continually with a deep layer of dry loose soil, which because of its looseness and dryness makes evaporation difficult.  A leading question in connection with cultivation is the depth to which the soil should be stirred for the best results.  Many of the early students of the subject found that a soil mulch only one half inch in depth was effective in retaining a large part of the soil-moisture which noncultivated soils would lose by evaporation.  Soils differ greatly in the rate of evaporation from their surfaces.  Some form a natural mulch when dried, which prevents further water loss.  Others form only a thin hard crust, below which lies an active evaporating surface of wet soil.  Soils which dry out readily and crumble on top into a natural mulch should be cultivated deeply, for a shallow cultivation does not extend beyond the naturally formed mulch.  In fact, on certain calcareous soils, the surfaces of which dry out quickly and form a good protection against evaporation, shallow cultivations often cause a greater evaporation by disturbing the almost perfect natural mulch.  Clay or sand soils, which do not so well form a natural mulch, will respond much better to shallow cultivations.  In general, however, the deeper the cultivation, the more effective it is in reducing evaporation.  Fortier, in the experiments in California to which allusion has already been made, showed the greater value of deep cultivation.  During a period of fifteen days, beginning immediately after an irrigation, the soil which had not been mulched lost by evaporation nearly one fourth of the total amount of water that had been added.  A mulch 4 inches deep saved about 72 per cent of the evaporation; a mulch 8 inches deep saved about 88 per cent, and a mulch 10 inches deep stopped evaporation almost wholly.  It is a most serious mistake for the dry-farmer, who attempts cultivation for soil-moisture conservation, to fail to get the best results simply to save a few cents per acre in added labor.

When to cultivate or till