Reference values of maximum daily trunk shrinkage for irrigation scheduling in mid-late maturing peach trees

Precise irrigation is essential in arid and semi-arid areas where water is scarce, such as the South-East of Spain. Therefore, finding a precise and reliable plant water status indicator, which could be automatically monitored, is of paramount importance. Maximum daily trunk shrinkage (MDS) showed some potential for irrigation scheduling. However, MDS records may be difficult to interpret and reference baselines could be useful for this interpretation. In the current study, measurements of midday stem water potential (Ψs) and MDS were taken over a 3-year period in peach trees [Prunus persica (L.) Batsch cv. 'Catherine'], in order to obtain reference baselines for irrigation scheduling. Plants were daily irrigated above their water requirements (∼120%) in order to obtain non-limiting soil water conditions. Climate parameters and MDS were recorded automatically, whereas midday stem water potential was assessed in the field every 3 days. The relationships between MDS and climate parameters such as ET0, daily maximum and midday air temperatures (Tmax and Tmid, respectively), maximum and midday air vapour pressure deficit (VPDmax and VPDmid, respectively) were determined. The results indicate that MDS records were better related to Tmid and Tmax than to other meteorological variables. The relationship between MDS and Ψs differed from year to year. However, these relationships varied greatly with the conditions of each year, tree phenological stage and crop load. Therefore, the growers must be aware of these factors when using MDS values for irrigation scheduling.