SAVING WATER BY CULTIVATION 53 



save soil moisture. In the Utah work such a soil was 

 found, from which one and one-half times more water 

 was lost during the growing season when cultivation was 

 practised. The natural mulching of this soil permitted 

 the lowest evaporation of a large series of tests with 

 several varieties of soil. Nevertheless, even on such soil, 

 the stirring of the soil carried with it other beneficial 

 results of high value to crops. That is, even though 

 cultivation on such soils may cause a greater loss of water, 

 the soil becomes able by the cultivation to produce more 

 dry matter with the water actually at its disposal. This 

 was well brought out in the Utah work, for the self- 

 mulching soil produced a crop 14 per cent larger on the 

 cultivated areas. 



Self-mulching soils are not plentiful, and too much 

 reliance should not be placed upon them. The irrigation 

 farmer is safe only when he cultivates his soils thoroughly 

 and frequently throughout the season. 



38. Time of cultivation. The rate at which water 

 soaks into a soil depends largely upon the physical con- 

 dition of the land. If the soil is coarse and loose, the down- 

 ward movement is rapid ;tif fine and compact, the down- 

 ward movement is slow. In any case the top soil remains 

 saturated or too wet for cultivation during several hours, 

 or days, after an irrigation. A sand or loam soil may often 

 be cultivated within one or two days after irrigation; but, 

 on a clay soil, this cannot be done until three to seven 

 days after irrigation. During this period before cultiva- 

 tion, when the top soil remains moist, evaporation losses 

 occur very rapidly. In fact, from one-fifth to one-third 

 of the loss due to evaporation throughout a three- or 

 four-week period occurs before the cultivator can be 

 applied to form a protective soil mulch. 



