Soil water content criteria for peach trees water stress detection during the postharvest period

Irrigation scheduling based on soil water moisture sensors requires that the soil water status be maintained within a range that is optimal for plant growth. The objective of this work was to evaluate whether soil water content dynamics, measured by multi-sensor capacitance probes, could be used to determine indices of a drying soil to detect the commencement of water stress in a peach tree orchard. For this, an experiment was carried out in a drip irrigated mature peach tree orchard in Murcia (Spain). During the postharvest period well irrigated trees (control treatment) were compared with two water stress treatments consisting of a drying cycle applied for one month in two ways: withholding irrigation (Rapid Stress) and progressively reducing irrigation (Gradual Stress). The soil water content (SWC) was measured continuously using multi-sensor capacitance probes. The beginning of plant water stress was identified by the first significant difference in midday stem water potential (Ψstem) between stressed and control trees. The ‘breaking point’ (the transition between a relatively rapid reduction of SWC in the drying soil to a slower rate) as well as the stabilization of the SWC-derived indices coincided with appearance of a water stress level as severe as to reduce plant water uptake, as judged from the Ψstem reduction. The results suggested that a lower SWC limit could be established for irrigation management in early maturing peach trees using capacitance probes at 90% of the field capacity value during the postharvest period.