112 STATE BOARD OF HORTICULTURE. 



examination. It was found that the plow-sole prevented the 

 irrigation water from reaching the deeper roots, and she was 

 advised to plow the entire orchard, roots and all, as deep as 

 the plow would go. This was done, much to the alarm of 

 many growers, and great numbers of orange roots of all sizes 

 were turned to the surface. Following further advice, she 

 irrigated and cultivated the ground deeply, and the following 

 season she harvested the largest crop ever taken from this 

 grove. 



The Glendora grove, to which allusion has been made, had 

 had deep cultivation from the beginning, and the roots were 

 mainly below the so-called hardpan. The McKenzie grove 

 had many roots in the hard "plow-sole," so that the only 

 remedy was to destroy these useless roots and force the growth 

 of new and deeper ones, at the same time giving the irrigation 

 water a chance to penetrate. This rather drastic root-pruning 

 was necessary, and if the Glendora grove had been cultivated 

 to a uniform depth a few more seasons, deeper plowing and the 

 destruction of the surface roots would have become inevitable 

 there also. The breaking-up of all hard layers of soil caused by 

 improper cultivation or careless use of water is of the first 

 importance to the health and profit of an orchard. 



After Mrs. McKenzie's experiment at Riverside, previously 

 mentioned, subsoilers of different forms were used, and the 

 idea soon became common among growers that the deeper 

 a plow could be run, the better would be the results that would 

 follow. The injurious results of such practice can not be 

 estimated without careful study of the root-systems of orange 

 trees on various stocks and soils. A number of bearing citrus 

 groves were so much injured by the reckless use of subsoil 

 plows that the leaves of the trees actually wilted down imme- 

 diately after the operation. In these cases, the sharp-cutting 

 plow was run close to and on all sides of the trees. When 

 trees over ten years of age, which have been subjected to uni- 

 form shallow plowing and irrigation, are submitted to such 

 treatment, they probably lose at one blow not less than seventy- 

 five per cent of their active roots. The shock is such that it 

 would take several years of careful treatment to restore the 

 trees. 



It is almost always more economical to use a subsoiler or 

 plow where " irrigation hardpan" has been formed than it is 

 to use the large amount of water necessary to soften it; but 



