Influence of Nitrogen Rate and Drip Application Method on Pomegranate Fruit Yield and Quality

Currently, 98% of domestic commercial pomegranate fruit (Punica granatum L.) are produced in California on over 13,000 ha.  Developing more efficient methods of water and fertilizer application are important in reducing production costs.  In 2012, a pomegranate orchard established in 2011 with a density of 558 trees/ha, was supplied nitrogen as N-pHURIC (urea-sulphuric acid, 10% N) and AN-20 (ammonium nitrate, 20% N) at rates of 52, 166, and 279 kg N/ha delivered by surface (DI) and subsurface drip irrigation (SDI) (at 61 cm depth).  Water replacement was based on rainfall, tree water removal, and soil surface water loss as measured by weather station ET_o and a weighing lysimeter. An additional 10% more water was applied by the DI system to compensate for efficiency differences between the two water delivery methods.  A fresh market (FM) harvest was made on Oct. 30 and a juice market (JM) harvest was then made on Nov. 8 to remove remaining fruits.  Total season yields (FM+JM) and average fruit weights were higher from trees irrigated by the SDI system compared to the DI system.  Fruit aril weight was greater, but soluble solids (SS) and juice color were lower in fruits from trees supplied by SDI compared to DI.  The Nov. 8 harvested fruits were smaller but had greatly enhanced juice color (measured spectrometrically and by CDM) compared to FM fruits.  Nitrogen rate had no effect on FM or total season yield, but fruit from trees supplied with 52 kg/ha were smaller in weight compared to fruit supplied higher N rates.  Increasing N rate had no effect on aril weight, SS (%) or juice color, but did reduce juice pH.  Total season yield was significantly improved by SDI only at the 52 kg/ha nitrogen rate.  JM juice color, but not FM juice color, was most intense (darkest) at the highest N application rate.  External FM fruit appearance (color) was not affected by N rate or water delivery method.