130 CALIFORNIA FRUITS: HOW TO GROW THEM 



three inches of dust spread over a hardpan layer formed in some soils 

 by cultivation, will not retain moisture well in California. The cultiva- 

 tor should go twice that depth, ordinarily, and then the result will be 

 accomplished if it is done frequently enough to prevent the re-firming 

 of the surface by atmospheric moisture or by the rise of moisture from 

 below. The exact significance of depth in the loose, surface layer has 

 also been demonstrated by moisture determination in the subsoil at 

 different points by the California Experiment Station, as follows : 



Percentage of Moisture in Cultivated Loam Soil. 



These may be accepted, probably, as average results : Variation 

 may occur in soils of different characters. The capillarity in a heavy 

 soil is vastly greater than in a light soil. The difficulty of securing a 

 pulverized surface layer is also greater in the heavy soil. The poorer 

 the pulverization, the deeper the layer must be. Naturally, then, grow- 

 ers' practice will vary. The rule will remain that there must be depth 

 enough to secure effective protection of the firm soil beneath from 

 agencies promoting evaporation. 



Loss of Moisture by Weed Growth. One of the most active 

 agencies for the exhaustion of moisture from the subsoil is the growth 

 of weeds. To cultivate the soil in winter and spring, and then to allow 

 a summer growth of weeds to "shade the soil" is a great error. Al- 

 though under cover of rank weeds moisture many appear even at the 

 surface and convey the impression of moisture-saving, the fact is, as 

 fully demonstrated by experience and actual experiment, the moisture 

 in the lower layers of the soil is reduced and trees are thus robbed of 

 their supply. Weed growth must be resolutely suppressed during the 

 dry season, if one has to operate by rainfall or desires to make best 

 use of irrigation water. 



Moisture Storage in the Soil. Conservation of moisture in the 

 soil is not only the surety of the current season's growth and fruitful- 

 ness, but is the safeguard against injury from the years of deficient 

 rainfall which occur now and then in California. The moisture supply 

 is equalized by this storage of the soil, and a surplus from the liberal 

 rainfall of one year is held over to supply the lack of the next. Of 

 course, the well-cultivated surface is also well calculated to catch water. 

 While from a hard surface much of a heavy rainfall flows off quickly 

 to a lower level before it can penetrate, a loose soil, if sufficiently deep, 

 retains all that falls upon it, except the excess, which disappears by 

 drainage. 



It has sometimes been held by California orchardists that planting 

 some tall-growing crop, like corn, so as to shade the young tree and 

 the ground around it, is an advantage. This is a great mistake. Though 

 some rich, moist soils may afford moisture enough to grow both the 

 tree and the corn, it is a fact that in most cases the growth of the corn 



