CULTIVATION OF CITRUS GROVES. 277 



ing roots through the iron-like layer of natural sub-soil 

 that is properly termed 'hard-pan.' When found to exist 

 it should be deemed sufficient to debar citrus culture, un- 

 less so thin that by boring or blasting the root system 

 can be established in good soil below the 'hard-pan/ or 

 when it is so constituted that when kept irrigated the 

 roots will penetrate it. 



"An instance of the latter occurred at Kiverside, 

 where Mr. Keed planted a few trees on a terrace border- 

 ing on an arroyo, and found what was reported as true 

 'hard-pan' near the surface. The trees received 'an abun- 

 dance of water over the whole area for a year,' and it 

 was then found that the roots had penetrated it to a con- 

 siderable distance. 



"The term 'irrigation hard-pan' is quite generally 

 used in some orange-growing districts to describe the 

 condition of some small areas in orchards where irriga- 

 tion and subsequent culture have been careless, 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 'irrigation 

 hard-pan,' by the puddling of the sub-soil, partly directly 

 by the plow, partly by the soaking in of clay-water. 



It is usual for orchardists to put in a sub-soil plow 

 to help in breaking up the heavy spots of what is called 

 'irrigation hard-pan.' But this difficulty can easily be 

 overcome without using a sub-soil plow, as was shown by 

 the experience of Mr. W. J. Cox, of Glendora, Los Ange- 

 les County, who found that 'irrigation hard-pan' was 



