EFFECT OF FOUR IRRIGATION RATES ON GROWTH OF SIX FIG TREE VARIETIES

Abstract

The fig tree is an attractive fruit crop for arid zones because of its tolerance to water deficit. However, there is very little information about its water requirements. A trial was conducted to determine the response of 4 leaf fig trees, in six varieties, to four irrigation rates in relation to estimated crop evapotranspiration (ETc), adapted for young trees and based on „Class A“ pan evaporation data. The irrigation treatments were T0 (not irrigated), T25 (25% ETc), T50 (50% ETc) and T100 (100% ETc). Rainfall in the region was 37 mm in the year of the study. The varieties were Brown Ischia (BI), Brown Turkey (BT), Kadota (K), Kennedy (KE), Larga de Burdeos (LB) and Royal Vineyard (RV), planted at 6 x 4 m. Significant differences in TCSA increase were observed in some treatments, except for var. BI and RV. Variety BT under T100 increased twice as much as under T50. In variety K , only T0 was different from T25. Regarding foliar area, significant differences were found only in varieties RV and LB, but in all others a good correlation between foliar area and TCSA increase, shoot length and leaf number was observed. In relation to shoot length only varieties BI and RV showed differences among treatments: T100 was significantly different to T0 and T25. In all treatments a good positive correlation between irrigation rate and shoot length was found. In xilem water potential, differences between T0 and T25, T50 and T100 were observed, but not between T50 and T100. In most varieties no differences between treatments in relation to phenological phase length were found. Most parameter showed no difference between T50 and T100. In conclusion, in the trial area, it‘s possible to irrigate 3-year old fig trees with 220 mm/year (2,200 m/ha-year), equivalent to 17% of „Class A“ pan evaporation. INTRODUCTION The fig tree is an attractive fruit crop for arid zones because of its tolerance to water deficit (Dominguez (1990)). However, there is very little information about its water requirements. Despite being considered a suitable crop for dry areas, its growth and development can be seriously affected by intense drought conditions (Melgarejo (1996)). Although the soluble solid concentration of fruit increases with a mild water deficit, irrigation is normally necessary at pre-harvest period in spring and summer. Irrigation in summer time is very important for growth of shoots, which are the points where the next season‘s first crop (brevas) and the second harvest of figs will occur. On the other hand, it must be recognized than the fig tree is a very sensitive plant to root rot, therefore excess of irrigation water must be avoided. (Dominguez (1990)). Regarding water quality, the fig tree is less demanding compared with other fruit tree crops, tolerating an electric conductivity of irrigation water up to 5.5 dS/m (Flores (1990), quoted by Melgarejo (1996)). D‘Andria et al. (1992) studied the productivity and vegetative growth of fig trees at different irrigation rates. Nonirrigated trees produced less fruit and less shoot length than irrigated ones. They also showed that there is good vegetative growth with irrigation equivalent to 50% of pan evaporation. In relation to the quantity and size of fruits, no significant differences between irrigation with 100% and 50% of ETc were found. Melgarejo (1996) indicates that one of the most important factor in fruit quality is the abrupt change in tree water status, which produces fruit cracking. In contrast, a wet soil