Effects of Seasonal Deficit Irrigation, Potassium Fertilization and Bunch Thinning on Growth, Yield and Quality of Flame Seedless Grapes

Abstract

Impacts of deficit irrigation levels, potassium fertilization, and bunch thinning on grapevine vegetative growth, yieldand quality of Flame Seedless table grapes were investigated during 2012 and 2013 seasons. Vines were subjected toseasonal irrigation treatments from bud swell to dormancy including: Standard irrigation (100 % of cropevapotranspiration [ETc]), moderate deficit (80 % of ETc), and sever deficit (60 % of ETc). Effects of two levels ofpotassium fertilization (0 and 0.58 kg as K2O per vine per season) and bunch thinning (40 and 30 bunch per vine) werealso investigated. Results showed that vine petiole potassium concentration was significantly dependent upon appliedirrigation level and was highest in standard irrigated potassium fertilized vines. Shoot length, leaf area and pruning weightresponded negatively to irrigation deficit, while bunch thinning increased leaf area in both seasons and pruning weight inthe second season with no effect on shoot length, whereas potassium had no effects on vegetative growth. Vine yield,bunch weight and berry diameter increased significantly with increasing irrigation level and with potassium fertilization.Bunch thinning significantly decreased yield in first season only while increased bunch weight and berry diameter. Cropload (yield/pruning) significantly increased by potassium and decreased by thinning with no effect for irrigation. Wateruse efficiency (yield/irrigation) significantly increased by increasing irrigation level and by potassium fertilization whiledecreased in first season by thinning. Increasing deficit irrigation level resulted in increased berry juice total soluble solids(TSS) and declined titratable acidity (TA), decreased berry firmness, increased skin anthocyanin and total phenolics, andreduced skin color characteristics values of lightness (L*), chroma(C*) and hue angle(h°). Bunch thinning increased berryTSS in first season, did not affect TA and fruit firmness, and increased berry skin anthocyanin and total phenolics, whiledecreased skin L* in the first season, C* and h°. Potassium fertilization increased berry TSS, TA, anthocyanin, totalphenolics, did not affect firmness with no consistent effect on skin color characteristics.