Preliminary assessment of the feasibility of using maximum daily trunk shrinkage for irrigation scheduling in lemon trees

The response of adult Fino lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus aurantium L.) to an irrigation schedule based exclusively on maximum daily trunk shrinkage (MDS) measurements was studied during the 2005 growing season. Plants irrigated above their crop water requirements (T0 treatment) were compared with plants under deficit irrigation. Reduced water application was based on MDS signal intensity (actual MDS/T0 treatment MDS) threshold values of around 1.25 (T1 treatment) and 1.35 (T2 treatment). When MDS signal intensity on at least two of three consecutive days did not exceed the MDS signal intensity threshold value, irrigation was reduced by 10%. When the MDS signal intensity on at least two of three consecutive days exceeded the threshold value the irrigation rate was increased by 10%. During the experimental period, the estimated crop evapotranspiration (ETc) was 536.9 mm and the cumulative amounts of applied water in T1 and T2 treatments were 396.3 and 220.3 mm, respectively. The results indicated that MDS measurements are suitable for adjusting the irrigation schedule, except in periods of very low evaporative demand, when some changes in the irrigation protocol should be introduced; using higher MDS signal intensity threshold values and/or lower irrigation frequency.