Maximum daily trunk shrinkage and stem water potential reference equations for irrigation scheduling of lemon trees

Measurements of midday stem water potential (psi(stem)) and maximum daily trunk shrinkage (MDS) were done over a 3-year period in adult Fino lemon trees (Citrus limon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that reference equations can be obtained for MDS and psi(stem) by pooling data across several seasons using crop reference evapotranspiration (ETo), daily mean vapor pressure deficit (VPDm) and mean daily air temperature (T (m)) in the case of MDS, and ETo in the case of psi(stem). The best predictor of MDS under non-limiting soil water conditions was T (m), suggesting that MDS reference values can be obtained by means of easy and cheap measurements. MDS and psi(stem) values were not influenced significantly by yield or crop load variations between years. A negative linear relationship between MDS and psi(stem) was found, pointing to an unchanging radial hydraulic conductivity in the bark tissues and suggesting that the MDS is controlled by water potential.