Yield and physiological responses of walnut trees in semi-arid conditions: application to irrigation scheduling
Résumé
The response of Serr walnuts (planted in 1987) to different irrigation treatments (20% ET c from June to September with 100% before and after the deficit period, 70, 100, and 130% ET c) was evaluated during 1992 and 1993 at Reus, Spain. Physiological, environmental and agronomic parameters were measured. Sap flow sensors enabled transpiration in the field under different irrigation conditions to be measured accurately. Trunk diameter variations appeared to be a good water stress indicator. Yield differences were primarily due to differences in fruit load since individual nut weight and size was not affected by irrigation regime. A 30% reduction (70% ET c) of irrigation reduced the total tree leaf area, yield, harvest indices and fruit size. This negative effect seems to be related to the deficit irrigation occurring during the rapid nut growth phase in May. The highest yields were obtained with 100% ET c. An additional supply of 30% water (130% ET c) only increased unnecessary vegetative development. The results suggest that trees irrigated with 20% ET c adapted by growing less but they were not less productive.