Is Soil Water Potential a Reliable Variable for Irrigation Scheduling in the Case of Peach Orchards?

Abstract

Monitoring the crop water status of high-value crops such as fruit trees is generally performed through periodic measurements of physiological indicators on leaves or fruits using sophisticated instruments and complex procedures. These measurements are very often difficult to translate into irrigation advice. Soil water potential (SWP), however, is a basic soil water status variable that is correlated with plant water uptake, and it can easily be measured using sensors. Soil water potential can provide useful support for irrigation scheduling at the field scale, thus enhancing water savings in agricultural areas. In this work, we present the results of an experimental study conducted in the 2014 agricultural season on a peach orchard located in Lodi (Northern Italy). The purpose of this study was to evaluate the effects of an irrigation scheduling based on continuous SWP measurements collected at two soil depths (−15 and −35 cm) on the crop water status and the peach production relative to the farmer’s commonly adopted irrigation practice. To answer the question in the title, periodic measurements of physiological parameters such as leaf water potential, stomatal resistance (rs), transpiration (E), and crop water stress index were performed, along with monitoring of fruit size evolution and fruit sugar content at harvest. All of these variables were measured to assess the crop physiological state of the trees subjected to the two different irrigation treatments, with the final objective of determining whether the irrigation scheduling based on SWP measurements compromised the quality and quantity of produced peaches. Although obtained for only one agricultural season, the results showed that no considerably crop water stress occurred, even for the irrigation treatment based on SWP measurements. In particular, the most extreme values of leaf water potential, rs, E, and crop water stress index measured at midday were −2 MPa, 45 s m−1, 1.4 mm h−1 and 0.5, respectively, which are in good agreement with those observed in many studies for well-watered orchards in Mediterranean areas. In conclusion, we can stress that SWP monitoring can be considered to be a reliable alternative to the more costly and time-consuming physiological measurements for the irrigation scheduling of fruit crops such as peach orchards. This approach provides continuous information about the soil water status, thereby preventing plant water stress and reducing irrigation water consumption at the farm scale.