456 SOILS. 



necessity of cultivation, involving the renewal of the sand each 

 season, renders this a costly method. Straw, leaves, and ma- 

 nure have been more successfully used; but even these, unless 

 employed for the purpose of fertilization, involve more ex- 

 pense and trouble than the simple maintenance of very loose 

 tilth of the surface soil throughout the dry season; a remedy 

 which, of course, is equally applicable to hoed field crops, and 

 is in the case of some of these e. g., cotton a necessary con- 

 dition of cultural success everywhere. The wide prevalence 

 of " light " soils in the arid regions, from causes inherent in 

 the climate itself, renders this condition relatively easy of ful- 

 filment. 



Turning-under of Surface Alkali. Aside, however, from 

 the mere prevention of surface evaporation, another favorable 

 condition is realized by this procedure, namely the comming- 

 ling of the heavily salt-charged surface-layers with the rela- 

 tively non-alkaline subsoil. Since in the arid regions the roots 

 of al! plants retire farther from the surface because of the 

 deadly drought and heat of summer, it is usually possible to 

 cultivate deeper than could safely be done with growing crops 

 in humid climates. Yet even there, the maxim of " deep prep- 

 aration and shallow cultivation " is put .into practice with ad- 

 vantage, only changing the measurements of depth to corre- 

 spond with the altered climatic conditions. Thus while in the 

 humid States, three to four inches is the accepted standard of 

 depth for summer cultivation to preserve moisture without 

 injury to the roots, that depth must in the arid region fre- 

 quently be doubled in order to be effective ; and will even then 

 scarcely touch a living root in orchards and vineyards, particu- 

 larly in unmanured and unirrigated land. 



A glance at fig. 63, chapt. 22, p. 431), will show the great 

 advantage of extra-deep preparation in commingling the alkali 

 salts accumulated near the surface with the lower soil-layers, 

 diffusing the salts, say through twelve instead of six inches of 

 soil mass. This will in very many cases suffice to render the 

 growth of ordinary crops possible if, by subsequent frequent 

 and thorough cultivation, surface evaporation, and with it the 

 re-ascent of the salts to the surface, is prevented. 



A striking example of the efficiency of this mode of proced- 

 ure was observed at the Tulare substation, California, where a 



