December 1, 1996
- controlled-release fertilizers
Young 'Hamlin' orange (Citrus sinensis [L.] Osb.) trees on 'Swingle' citrumelo (C. paradisi Macf. × Poncirus trifoliata [L.] Raf.) rootstock were interset in a 10-year-old 'Hamlin' orange grove. The objective was to compare various irrigation schedules, emitter patterns and fertilizer types for optimizing interset growth while minimizing costs. Trees were irrigated using 90ordm;, 180ordm; or 360ordm; 10 gph microsprinklers for either 2 (young tree) or 4 (mature tree) hours based on an available soil water content (SWC) of 70% for young trees or 70% Jan.-June and 50% July-Dec. for mature trees. One half of the trees in each group were either fertilized 5 times/year with dry, water soluble (8N-2P[sub2]O[sub5]-8K[sub2]O) material or once/year with Sherritt® controlled-release fertilizer (44.5N-0P[sub2]O[sub5]-45K[sub2]O). Trees on the young tree program were irrigated 27 and 17 times/year in 1993 and 1994, respectively, while those on the mature tree program were irrigated 15 and 11 times/year, respectively. SWC was generally lower for interset trees irrigated using 360ordm; vs 180ordm; or 90ordm; emitters, although SWC was usually greater than 70% for all emitter patterns. Mean trunk diameter after years 1 and 2 in the field was similar for all emitter types, and both irrigation schedules. The dry fertilizer produced statistically but not noticeably larger trunk diameters than the controlled-release fertilizer. Therefore, interset trees may be watered on a mature tree schedule and fertilized once/year using controlled release materials without significantly decreasing growth during the first 2 years in the field.