Loss in Uncultivated Soit. 141 
CULTIVATED. UNCULTIVATED. 
DEPTH IN SOIL. 
Per cent, ce er | Per cent. pie! ge 
First f00tssccwsessvereveuteieatverience| 6.4 128 4-3 * 86 
Second foot 5.8 116 4-4 88 
Third foot .....c.ccceeeeesee 6.4 128 3.9 78 
Fourth foot.........0. see 6.5 130 5.1 102 
Fifth foot... cece 6.7 134 3-4 68 
Sixth foots ccavsssvevssrenssceasvassssesares 6.0 120 4.5 go 
Total for six feet... seen 6.3 756 4.2 512 
This shows a gain of nearly fifty per cent of soil moisture 
by cultivation. 
Necessity of Adequate Cultivation—It has been very fully 
demonstrated by California experience that adequate depth of 
tilth must be attained. The depth of cultivation, or the thickness 
of the dust-mulch, as some like to call it, must be sufficient to 
prevent the access of the dry air to the firm soil below. At the 
East, where they have a moister air, a thin mulch may answer; 
but in California, with a thirsty air for such a protracted period, . 
there must be deeper tilth. Two or three inches of dust spread 
over a hard-pan layer, formed in some soils by cultivation, will 
not retain moisture well in California. The cultivator should 
go twice that depth, ordinarily, and then the result will be accom- 
plished 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, sur- 
face 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. 
Depth. Niles. Santa Maria. Ventura. 
Three inches. 5.4 5.3 6.5 
Six inches. 6.3 8.3 9.3 
These may be accepted, probably, as average results: varia- 
tion may occur in soils of different characters. The capillarity 
in a heavy soil is vastly greater than in a light soil. The diffi- 
culty 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, growers’ practise 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 
