8 BULLETIN 71, HAWAII EXPERIMENT STATION 



container at the time of planting, care being taken to avoid 

 disturbing the soil about the roots. The young trees should be 

 set firmly by lightly tramping the soil as the holes are filled. The 

 natural ground line of the tree should be an inch or two above 

 the natural surface of the orchard (fig. 2, A, c), particularly in 

 heavy soil. High planting is believed to prevent several forms 

 of gum diseases that affect citrus trees. In Puerto Rico, Hen- 

 ricksen (15, p. 21, 33) found that the planting of citrus trees on 

 mounds effectively safeguarded them from foot rot, a gum dis- 

 ease doing considerable damage to citrus trees planted too deep. 



Immediately after they are planted, the trees should be liber- 

 ally watered. Temporary shading is not necessary if the plant- 

 ing is well done and the trees were exposed to the sun during 

 their last month in the nursery. A vigorous, vegetative growth 

 should be maintained during the first few years to enable the 

 trees to produce good crops. 



Tillage 



The best results are obtained with the tillage necessary to 

 produce spring and fall cover crops. Turning the cover crop 

 under in early spring has been satisfactorily practiced at the 

 station. If the herbage is high it should be cut finely with the 

 disk and turned under to a depth of 6 or 8 inches with the plow. 

 A few days later the plowed field should be disked to pulverize 

 the surface, and the seed either drilled in, or broadcast and 

 harrowed. Weeds should be destroyed. 



Irrigation 



In most parts of Hawaii occasional prolonged drought may 

 injure the growth of orchard crops. There are also good citrus- 

 growing localities where irrigation is necessary every spring 

 and summer. The windward slopes of the islands usually are 

 favored with an adequate rainfall, but the warm leeward slopes 

 where irrigation is possible afford the best results with citrus. 

 Irrigation is generally applied in shallow basins about the base 

 of each tree trunk. The method is not satisfactorily used on 

 heavy soils. They soon become "water-logged," a condition fa- 

 vorable to the development of gum diseases. Under this method 

 on heavy soils much of the water is lost by deep percolation and 

 soluble plant food is carried below the root zone. Citrus trees 

 should not be set too low in the ground and the basins should be 

 leveled at the beginning of the second year and a moat provided 

 1 or 2 feet from each tree for the irrigation water. The moat 

 should be maintained from year to year above the feeding roots. 



The irrigation water may be conducted to the highest point 

 of the orchard through concrete or iron pipes, or, on compara- 

 tively heavy soil, through open ditches, preferably of stone, con- 

 crete, or wood (12. p. 4-20). From the highest point the water 

 may be delivered to the moat of each tree through temporary 

 furrows made between tree rows with a furrower. The grade 

 of the furrows should be less than 10 percent so that the water 

 will flow gently and not wash the fine soil to lower levels. The 

 short ditches connecting the furrows with the moats may be 



