Using continuously recorded trunk diameter fluctuations for estimating water requirements of lemon trees

Adult Fino lemon trees (Citrus limon L. Burm. fil.) grafted on sour orange (Citrus aurantium L.) and irrigated above their crop water requirements (T0 treatment) were compared with plants where water was applied according to maximum daily trunk shrinkage (MDS) (T1 treatment), in order to maintain MDS signal intensity [actual (T1) MDS/control (T0) MDS] threshold values close to unity. When MDS signal intensity on at least 2 of 3 consecutive days did not exceed the signal intensity threshold value, irrigation was reduced by 10%. In contrast, when the MDS signal intensity on at least 2 of 3 consecutive days exceeded the threshold value, the irrigation rate was increased by 10%. The results indicated that lemon tree irrigation scheduling can be based on MDS measurements, avoiding the appearance of any plant water stress situation without affecting yield or fruit quality. Also, the cumulative amounts of applied water in T1 plants can be considered as an estimate of lemon tree water requirements, because they were only 9% above the estimated crop evapotranspiration (ETc) and drainage did not occur. Nevertheless, to improve the precision of irrigation management, some changes in the irrigation protocol for periods of variable evaporative demand were proposed: for instance, increasing the irrigation scheduling frequency and/or using changes in the daily irrigation rate higher than those proposed in the protocol.