CITRUS CULTURE IN HAWAII 



9 



made with a hand shovel or with a hoe, and the amount of 

 water for each tree may be regulated by filling the short ditch 

 with several shovelfuls of soil to form a gate. 



Some growers who have water under pressure are satisfied 

 with a pipe system. According to the pressure the system may 

 be constructed of 1-, IV2-, or 2-inch galvanized iron pipe laid at 

 a depth of 15 inches and arranged to give one upright with 

 faucet for each 9 trees. A hose is used to carry the water from 

 faucet to any of the 9 moats. Overhead irrigation is described 

 by Coit (7, p. 198-199), but it has been seldom practiced in Ha- 

 waii. Thomas {27, p. 353) found that California growers gen- 

 erally "followed certain arbitrary rules, especially in regard to 

 the frequency of application and the amount of water applied." 

 In his opinion, irrigation furrows that exceed 250 or 300 feet 

 in length are undesirable. The amount of water required for 

 good growth depends on temperature, humidity, rainfall, the 

 nature of the soil, and the age of the trees. 



Intercropping 



A short-time crop should be kept growing between the trees 

 as a source of revenue or as a green manure. Such short-time 

 crops as peas, beans, carrots, beets, tomatoes, sweet potatoes, 

 and upland taro are best adapted to the lower elevations during 

 the winter and the early spring. The roselle, poha, cabbage, and 

 other plants adapted to the lower temperatures also may be used 

 at elevations above 800 feet. Such perennials as papayas and 

 alfalfas are sometimes grown. A single row of passion fruit 

 (Passiflora edulis), midway between orchard rows of citrus, is 

 being grown at the Kona substation, at an elevation of 1,500 

 feet. Intercropping in the young citrus orchard should be dis- 

 continued at the end of five years so that it will not interfere with 

 the development of the trees. Intercropping should not be prac- 

 ticed on heavy soils with plants requiring frequent watering. 



Cover Crops 



Cover crops for green manuring greatly benefit Hawaiian 

 soils, many of which are deficient in organic matter. The cover 

 crop when turned under returns to the soil all the fertilizing 

 elements that were removed in the making of the crop and adds 

 humus or organic matter which greatly improves the texture 

 and the moisture-holding capacity of the soil. According to 

 Piper and Pieters (20, p. 5), soils vary greatly in their water- 

 holding capacity, and the addition of humus affects both the 

 physical and the chemical properties of the soil. They state 

 that 100 pounds of sand can hold only 25 pounds of water and 

 100 pounds of clay 50 pounds, whereas the same weight of humus 

 will hold 190 pounds. Humus increases the water-holding capa- 

 city of the soil and makes it workable. Humus is also helpful 

 in the formation of bacteria which make available great stores 

 of inert plant food in the soil. Leguminous cover crops aid in 

 increasing the nitrogen content of the soil. In most localities 

 cover crops are maintained during the season of heavy rainfall 



