'166 



The term ''irrigation hardpan" is quite generally used in the 

 orange-growing district to describe the condition of some small areas 

 in orchards where irrigation and subsequent culture have been care- 

 less, or where sufficient attention has not been paid to the difference of 

 treatment required by lighter and heavier soils. 



Of course very sandy soils can be handled sooner after irrigation 

 than can heavier soils and when a sandy piece of land containing 

 areas of heavy soil is cultivated as soon after irrigation as the sandiest 

 part will permit, trouble may be expected with the so-called " irriga- 

 tion hardpan," by the puddling of the subsoil, partly directly by the 

 plough, partly by the soaking in of claywater. 



Value of proper CulUvation. — It is usual for orchardists to put in a 

 subsoil plough to help in breaking up the heav}' spots of what is called 

 " irrigation hardpan." But this difficulty can easily be overcome 

 without using a subsoil plough, as was shown by the experience of Mr. 

 "W. J. C(»x, of Glendora, Los Angeles County, who found that "irri- 

 gation hardpan" was forming in a part of his orange grove. He irri- 

 gated a few trees that were within reach of ihe domestic water-supply 

 and followed this up at the proper time with thorough cultivation. 

 After each irrigation he cultivated a little deeper. As a result of 

 deep irrigation and cultivation, the soil took in water as readily as 

 ever and the trees regained their vigorous appearance. He simply 

 used a chisel-tooth cultivator and plenty of water. 



A somewhat different, case was that of Mrs. McKenzie of Riverside, 

 whose orange grove failed to be profitable, though apparently well 

 irrio-ated. This orcha d had been cultivated to the same depth until 

 a hard, clav "plough-sole" had been formed. The stratum of hard sub- 

 soil was several inches thick and contained a number of large surface 

 roots. She wrote to the Californian Experiment Station, sending 

 samples of soil for examination. It was found thas the plough -sole 

 prevented the irrigation water from reaching the deeper roots, and 

 she was advised to plough the entire orchard, roots and all, as deep as 

 the plough 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 Glondora 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 " plough-sole" so thatthe 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 (ilendora grove had been culti- 

 vated to a uniform depth a few more seasons, deeper ploughing 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. 



Eec/iless Deep Cultivation. — 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- 



