Is the soil water potential a reliable variable for irrigation scheduling in case of peach orchards?

Crop water status monitoring in the case of high-value crops such as fruit trees is generally carried out through periodic measurements of physiological indicators on leaves or fruits operated by sophisticated instruments and complex procedures. These measurements are very often difficult to translate in an irrigation advice. Soil water potential (SWP), on the contrary, is a basic soil water status variable correlated with plant water uptake, which can be easily measured by sensors. It can provide a useful support for irrigation scheduling at the field scale, enhancing the water saving in agricultural areas. In this work we present the results of an experimental activity carried out in the agricultural season 2014 on a peach orchard located at Lodi (Northern Italy), with the purpose of evaluating the effects of an irrigation scheduling based on continuous SWP measurements collected at two soil depth (-15 and -35 cm) on the crop water status and the peach production, with respect to the farmer’s commonly adopted irrigation practice. In order to answer the question in the title, periodic measurements of physiological parameters such us leaf water potential (LWP), stomatal resistance (rs), transpiration (E) and crop water stress index (CWSI) were performed, in association with the monitoring of fruit size evolution and fruit sugar content at the harvest. Al these variables were detected to assess the crop physiological state of the trees subjected to the two different irrigation treatments, with the final scope to show if the irrigation scheduling based on SWP measurements compromised the quality and quantity of the peach production. The results showed that, even for the irrigation treatment based on SWP measurements, no considerable crop water stress occurred. In particular, the most extreme values of LWP, rs, E, and CWSI measured at midday were respectively -2 MPa, 45 s m-1, 1.4 mm h-1 and 0.5, in good agreement with those observed by many researches for well-watered orchards in Mediterranean areas. In conclusion, we can stress that SWP monitoring can be considered a reliable alternative to the more costly and time consuming physiological measurements for the irrigation scheduling of fruit crops such as peach orchards, providing continuous information about the soil water status, preventing the plant water stress and reducing the irrigation water consumption at the farm scale.