CITRUS CULTURE IN HAWAII 



11 



two latter elements. Lava soils have sufficient calcium for most 

 plants. For desired plant growth often nitrogen has to be added 

 in the form of nitrate of soda, or as a superphosphate of am- 

 monia. The former is quicker in its action than the latter. 

 Organic nitrogen may also be added to the soil in the form of 

 dried blood, tankage, or other plant and animal material. Barn- 

 yard manure is a complete fertilizer and is usually rich in_ ni- 

 trogen. Less nitrogen and more potash in the complete fertilizer 

 is recommended to improve maturing citrus fruits, the nitrogen 

 being reduced from 5 to 3 percent, and the potash increased from 

 3 to 5 percent. 



In a young experimental citrus orchard in Kona, fertilizer 

 is being applied according to the plan of Vosbury and Robinson 

 (29, p. 27). In Hawaii the time of application may vary with 

 the most active growing season in different localities. For ex- 

 ample, on the island of Hawaii the rainfall of the Hamakua 

 (northeastern) coast is greatest in the winter, and in Kona, on 

 the west side, it is greatest from April to November, while in 

 Puna, on the southeast, it is comparatively uniform throughout 

 the year. One-year-old grafted citrus trees, with roots washed 

 clean of all soil to comply with the quarantine regulations, were 

 planted early in the spring of 1931 in soil moderately incorpor- 

 ated with barnyard manure. In the summer of 1931, after new 

 growth appeared, 1 pound of a complete fertilizer rather rich 

 in nitrogen was applied to each tree. This was worked into the 

 surface soil around the tree with a hoe and was followed by 

 vigorous growth in the fall of 1931, when a second application 

 was made. The third application, at the rate of 2 pounds to a 

 tree, was made in April, 1932, at the beginning of the growing 

 season, and a fourth application, at the rate of 2 pounds to a 

 tree, was made in midsummer, 1932. Applications will be in- 

 creased a pound to a tree until it begins to bear. Complete fer- 

 tilizer will then be applied during the summer, but the nitrogen 

 will be reduced to 2 percent. After the trees have borne for 10 

 years the amount of commercial fertilizer may be increased 

 about a pound a year for the next 15 years. This amount of fer- 

 tilizer and the plowing under of one or two green-manure crops 

 should maintain soil fertility and orchard production. 



Pruning 



The citrus orchard should never be severely pruned. The 

 tops should be cut back at the time the trees are planted to main- 

 tain a balance between the top and the roots that were pruned 

 at the time of transplanting. The first 5 or 6 years should be 

 devoted mostly to the production of a strong symmetrical tree. 

 The branches forming the framework of the top should arise 

 from the upper part of the trunk, be well-spaced and so shaped 

 as to sustain heavy crops. The foliage should shelter the frame- 

 work but not be so dense in the interior as to exclude light and 

 air. _ Severe pruning, with the lemon in particular, may lead to 

 a vigorous growth of water sprouts and resultant decreased 

 yields. The object of pruning is to stimulate vegetative growth, 

 remove undesirable branches, and increase the rate of growth 



