Authors: RIZA KANBER, HARUN KÖKSAL, ATİLLA YAZAR, BÜLENT ÖZEKİCİ, SERMET ÖNDER
Abstract: Long-term field experiments were carried out between 1985 and 1988 to determine the effect of different irrigation intervals and pan coefficients on the fruit and trunk growth rates and yield of mature grapefruit trees grown in the Eastern Mediterranean Region of Turkey in a medium-light textured soil. Two different irrigation intervals (I 1 =15 and I 2 =25 days), and pan coefficients (k 1 =0.60 and k 2 =1.00) were used. Higher evapotranspiration values were obtained from the treatments with k 2 coefficient in the two irrigation regimes. The average irrigation water (IR) and evapotranspiration (Et) values were 796 mm and 1039 mm for I 1 k 2 , and 782 mm and 988 mm for I 2 k 2 , respectively. The grapefruit trees exhibited periodicity during the period of study. Results indicate that the effects of the irrigaiton programs on grapefruit yield were not significantly different. However, slightly higher yields were obtained from the frequently irrigated trees with an average of 67.3±0.164 t/ha for I 1 k 1 . In periodicity years, the yield and the number of fruits harvested decreased by 45-52% and 77-85% with respect to irrigation treatments. In normal-yield years, the average fruit weight and diameter were nearly 32% and 20% lower than in the periodicity years, and the seed number was two to four times greater than in the periodicity years. It was found that there was an inverse relationship between fruit extract and TSS (total soluble solid percentage). The fruit extract content increased to 41.9%, whereas TSS decreased to 11.1% in normal-yield years. Fruit extract and peel thickness varied during the experimental period. In the periodicity years, the average fruit extract was about 17% lower and the peel thickness was 18% higher than in normal-yield years. Both the fruit and trunk-diameter growth rates were higher in treatment I 1 k 1 than the ohers. The maximum development in trunk diameters was observed in I 1 k 1 , with 23% (above the graft) and 28% (below the graft), and 35% in terms of fruit diameter. The relationship between yield and some quality characteristics in the estimation of the yield was analyzed. The effects of various factors on the yield were determined using multiple regression analysis. The equation Y=-141.518+0.058FN-10.359NS can be used to estimate the final yield o grapefruit where FN is the fruit number, and NS is the number of segments. However, it was shown that measurement of fruit diameter during certain periods of the year can be used to predict grapefruit yield. For this purpose, the equation Y=162.681+56.819(X 16 )-17.650(X 19 )-41.100(X 20 ) can be used, where X16, X19, and X20 are the fruit diameters observed on August 15, September 30, and October 15, respectively.
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