MULCHED-BASIN SYSTEM OF IRRIGATED CITRUS CULTURE. 329 
of a plowsole, or incipient hardpan, below the surface mulch, vary- 
ing in thickness from 3 inches to 2 feet; leads to excessive accumula- 
tions of soluble plant-food substances, especially nitrates, at the sur- 
face of the soil, where they remain until washed down by the winter 
rains; and fails to conserve the soil moisture sufficiently to prevent 
the trees from wilting frequently during the summer months. 
The mulched-basin system was found to conserve the soil mois- 
ture better than any other system of soil treatment compared with 
it, and none of the basined trees on either light or heavy soils wilted. 
Under all the other cultural methods employed wilting occurred at 
some period during the summer on both light and heavy soils. 
Available soil moisture below the third foot did not prevent orange 
trees from wilting if the moisture content in the first 3 feet of soil 
fell below the wilting coeflicient. 
With the amount of irrigation water ordinarily available in these 
districts (1 miner’s inch to 4 or 5 acres) cover crops of barley or 
sweet clover can not be grown during the summer months in groves 
on either heavy or light soils without causing the wilting of the 
orange trees. 
Circular trenches dug around orange trees, filled with manure or 
alfalfa and covered with dirt, did not remain open sufficiently after 
the second irrigation to distribute the irrigation water adequately. 
In the clay-loam soils of the type constituting the Victoria area 
the lateral movement of moisture is very slight. In such soils the 
furrow system of irrigation is inadequate unless a large number of 
furrows are used, including furrows under the trees. 
Moisture determinations in groves in which alfalfa was being 
grown as a permanent cover crop show that the irrigation water 
never penetrated deep enough into the soil to insure an adequate 
moisture supply for the orange trees. 
For a basin having an area of 150 square feet the experiments 
indicate that approximately 150 pounds of alfalfa or 15 to 20 cubic 
feet of stable manure will be required each year to maintain an 
effective mulch. 
It is not possible with the water ordinarily available to grow 
mulching material between the basins sufficient to maintain a satis- 
factory mulch on the basins. Cover crops, however, can be grown 
between the basins on winter rainfall to supply part of the mulch, 
and where water is available in the summer it can be used for the 
same purpose. 
Orange trees on clay-loam soil, such as the Victoria soil, responded 
more quickly to the mulched-basin system than trees similarly treated 
on light soils, because the heavier soils under the furrow method of 
irrigation do not absorb moisture as rapidly as lighter soils. Mulched- 
basined trees on clay-loam soils showed a marked response to the 
