Salinity effects on Florida grapefruit in the Indian River Region

A study was initiated in the 1997-98 production season to evaluate the effects of salinity on grapefruit yield and fruit quality in the Indian River area of Florida. The experiment was conducted on 'Ray Ruby' grapefruit (Citrus paradisi) planted in 1990 on 'Carrizo' citrange (C. sinensis x Poncirus trifoliata) and 'Swingle' citrumelo (C. paradisi x P. trifoliata) rootstocks. Trees were planted on 15.2-m-wide (50 ft) double-row beds at a spacing of 4.6 m (15 ft) in-row x 7.3 m (24 ft) across-row [286.6 trees/ha (116 trees/acre)]. The control treatment was irrigated via microsprinkler emitters with water from a surficial aquifer well with an electrical conductivity (EC) of 0.7 dS.m(-1). Higher irrigation water salinity levels were achieved by injecting a sea water brine mixture into the supply water to achieve ECs of 2.3, 3.9, and 5.5 dS.m(-1). A wide range of rainfall and irrigation conditions occurred during the years encompassed by these studies, with rain totaling 1262, 1294, 1462, and 964 mm (49.7, 50.9, 57.6, and 38.0 inches) for 1997, 1998, 1999, and 2000, respectively. Salinity level had little effect on internal juice quality parameters [total soluble solids (TSS), acid, or juice content] at time of harvest. One of the most visible effects of irrigation with high salinity water was the damage to leaves, with leaf chloride (Cl) levels increasing about 0.14% for each 1.0 dS.m(-1) increase in EC of the irrigation water for trees on 'Carrizo' citrange and 0.02% for trees on 'Swingle' citrumelo. For both rootstocks, the number of fruit and the size of the fruit decreased with increasing salinity in the irrigation water. The non-salinized trees had significantly larger fruit compared to the rest of the treatments. In the very dry 2000-01 season, trees on 'Carrizo' irrigated with 0.7 dS.m(-1) water had about 50% more fruit size 36 [fruit count per 0.028-m3 (4/5 bu) carton] or larger than trees watered with 3.9 or 5.5 dS.m(-1) water. For trees on 'Swingle' rootstock, trees irrigated with 0.7 dS.m(-1) water had 150% to 200% more size 36 and larger fruit than trees watered with 2.3 dS.m(-1) water. Over the four seasons, average yields for 'Carrizo' were reduced 3200.0 kg.ha(-1) (2855 lb/acre) per year for each 1.0 dS.m(-1) increase in EC of the irrigation water. For 'Swingle' rootstock, the reduction was 2600.3 kg.ha(-1) (2320 lb/acre) per year for each 1.0 dS.m(-1) increase in EC of the irrigation water. These reductions averaged 7% ('Swingle') and 6% ('Carrizo') for each 1.0 dS.m(-1) increase in salinity of the irrigation water.