Soils, Fertilizers and Irrigation 141 



Soil Depth for Citrus Trees. 



/ liaz'c a top soil of rich loam containing small rocks and pebbles. 

 Underneath it is zvashed gravel, rocks, boulders, yelloiv sand, etc. What 

 is the limit as to thinness before trees will not grow, or thrive? 



Orange trees arc growing quite successfully on shallow soil over- 

 lying clay where the use of water and fertilizers was carefully adjusted 

 so as to keep the trees supplied with just the right amount. Under 

 such conditions a good growth may he expected so long as this treat- 

 ment is maintained. There should he, however, not less than three 

 feet of good soil to make the large expenditure necessary to estahlish 

 an orange orchard permanently productive, and all the depth you can 

 get beyond three feet is desirable. We question the desirability of 

 planting orange trees even on a good soil overlying gravel, rocks or 

 sand. Roots will penetrate such material only a short distance usu- 

 ally. It is almost impossible with such a leachy foundation to keep 

 the surface soil properly moistened and enriched. You are apt to lose 

 both water and fertilizer into the too rapid drainage. 



Soils and Oranges. 



/ find this entire district underlaid with hardpan at various depths, 

 from I to 6 feet down, and of various thicknesses. This hardpan is 

 more or less porosis and seeps up water to some extent, but is too hard 

 for roots to penetrate. It is represented to me that if this hard pan 

 is down from 4 to 5 feet it does not interfere with the growth of thd 

 orange tree or its producing. Is 4 or 5 feet of the loam enough? 



Four or five feet of good soil over a hardpan, which was some- 

 what porous, is likely to be satisfactory for orange planting. There 

 has been trouble from hardpan too near the surface and from the oc- 

 currence of a hardpan too rich in lime, which has resulted in yellow 

 leaf and other manifestations of unthrift in the tree. Discussion of 

 this subject is given on page 434 of the fifth edition of our book on 

 "California Fruits," where we especially commend a good depth of 

 "strong, free loam." This does not mean necessarily deep. The or- 

 ange likes rather a heavier soil, while a deep sandy loam is preferred 

 by some other fruits. If you keep the moisture supply regular and 

 right and feed the plant with fertilizers, as may be required, the soil 

 you mention is of sufficient depth — if it is otherwise satisfactory. 



Oranges Over High Ground Water. 



Does California experience shozu that citrus trees can be groivn upon 

 land successfully zvhere the zvater-lcvcl is 6 feet from the surface; that 

 is, where water is found at that level at all seasons and does not appear 

 to rise higher during the rainy season? 



We do not know of citrus trees in California with ground-water 

 permanently at six feet below the surface. If the soil should be a free 

 loam and the capillarity therefore somewhat reduced, orange trees 

 would probably be permanently productive. If the soil were very 



