276 CITRUS FRUITS AND THEIR CULTURE. 



Cultivation in Relation to Irrigation. Perhaps the 

 most important thing to be considered in those districts 

 where irrigation must be carried on is the relation be- 

 tween cultivation and irrigation. One of the best dis- 

 cussions of this phase of citrus culture is that given by 

 J. W. Mills in Bulletin No. 138 of the California Experi- 

 ment Station, here reproduced in full: 



"In order to achieve the highest results, it becomes 

 more and more essential that the grower shall keep the 

 soil in the most perfect condition, shall apply all needed 

 water and plant food in sufficient, but not in excessive, 

 amounts, and shall pay especial attention to keeping the 

 feeding roots as low as practicable, and to preventing 

 the formation of what is called 'hard-pan/ but is only 

 the well-known 'plow-sole/ aggravated by shallow irriga- 

 tion. 



" 'Hard-pan/ some growers say, appears now where 

 it was never known before. The fibrous roots of orange 

 trees run along the surface and thus are subject to every 

 vicissitude. It often happens that what orchardists call 

 'hard-pan' is only the firm layer of soil caused by uniform 

 cultivation, or plowing, whether deep or shallow. The 

 depth to which the soil is stirred should vary from year 

 to year; eight inches, twelve inches, ten inches, fourteen 

 inches, and then eight inches again, would put an end to 

 much of the present outcry against 'hard-pan.' Cultiva- 

 tor teeth should always be kept sharp and should be 

 'set down' to various depths, so as to prevent the forma- 

 tion of 'plow-sole' of any description, and to assist in 

 breaking up that which former neglect has caused. 



"Very few orange groves have been planted upon true 

 'hard-pan' and if so planted have seldom succeeded. Only 

 a few trees, such as our native oaks, are capable of thrust- 



