MULCHED-BASIN SYSTEM OF IRRIGATED CITRUS CTJLTTJBE. 20 



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 preveni 

 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 coefficient. 



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 



