Impacts of deficit irrigation levels, potassium fertilization, and bunch thinning on grapevine vegetative growth, yield
and quality of Flame Seedless table grapes were investigated during 2012 and 2013 seasons. Vines were subjected to
seasonal irrigation treatments from bud swell to dormancy including: Standard irrigation (100 % of crop
evapotranspiration [ETc]), moderate deficit (80 % of ETc), and sever deficit (60 % of ETc). Effects of two levels of
potassium fertilization (0 and 0.58 kg as K2O per vine per season) and bunch thinning (40 and 30 bunch per vine) were
also investigated. Results showed that vine petiole potassium concentration was significantly dependent upon applied
irrigation level and was highest in standard irrigated potassium fertilized vines. Shoot length, leaf area and pruning weight
responded negatively to irrigation deficit, while bunch thinning increased leaf area in both seasons and pruning weight in
the 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. Crop
load (yield/pruning) significantly increased by potassium and decreased by thinning with no effect for irrigation. Water
use efficiency (yield/irrigation) significantly increased by increasing irrigation level and by potassium fertilization while
decreased 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, and
reduced skin color characteristics values of lightness (L*), chroma(C*) and hue angle(h°). Bunch thinning increased berry
TSS in first season, did not affect TA and fruit firmness, and increased berry skin anthocyanin and total phenolics, while
decreased skin L* in the first season, C* and h°. Potassium fertilization increased berry TSS, TA, anthocyanin, total
phenolics, did not affect firmness with no consistent effect on skin color characteristics.