The 2011 ASHS Annual Conference

Freeze damage is often the most limiting factor for Satsuma mandarin production in Alabama.  Currently, various orchard designs are being employed to minimize the risk of freeze damage.  These orchard design strategies include planting in open fields with microsprinkler irrigation, interplanting between pine and pecan trees, and planting behind windbreaks. The goal of this study was to evaluate the effects of different orchard designs on orchard temperature, photosynthesis, leaf characteristics, fruit quality and yield.  Five orchards planted with ‘Owari’ Citrus unshui grafted onto ‘Rubidoux’ Poncirus trifoliata were selected based on their orchard design, and four trees were selected as experimental units within each orchard.  For each experimental unit, a temperature data logger was placed approximately 1.5 m high on the exterior of the canopy, and in an open area outside the orchard for comparison.  The orchards that were interplanted with mature pine trees had the greatest insulating effect on temperature when compared to the control.  In addition, Satsuma mandarin trees grown under pine tree canopies appeared to experience less yield loss in 2010 following a significant freeze event.  However, yield appeared to be greatly reduced under dense pine tree canopy in 2009, when freeze damage was not experienced.  The fruit from shaded orchards tended to be smaller and have reduced rind thickness compared to other orchard designs.  Typical of smaller mandarin fruit, shaded fruit had higher percent soluble solids.  As expected, trees grown under continuous shade had reduced rates of photosynthesis, greater leaf areas, and greater specific leaf area (thinner leaves).  In summary, orchard design, specifically growing Satsuma mandarins under mature pine tree canopies, can moderate temperature resulting in higher yields when freeze events occur.  However, continuous shade also affects plant physiology and fruit quality, and potential maximum yields are reduced when environmental conditions are favorable.