Recommendations for water conservation in peach orchards in Mediterranean climate zones using combined regulated deficit irrigation

The results of three different studies of combined regulated deficit irrigation (RDI) under different soil depth conditions were compared for horticultural effects (fruit growth, bloom density and fruit set) and changes in relief patterns of water stress. One study was carried out under shallow soil (< 0.5 m) conditions (SSE-50) with irrigation rates for RDI trees being respectively reduced to 0.5 and 0.35 of a full irrigation Control treatment during Stage II of fruit development and Postharvest. In another study, on deep soils (> 2 m) (DSE-35), irrigation rates for RDI trees were reduced to 0.35 of the Control treatment during both Stage II and Postharvest. In the third experiment, soils were also deep, but irrigation during Stage II was withheld for RDI trees (DSE-NI). Plant water deficit was estimated by means of midday stem water potential (psi(stem)). On deep soils a detrimental effect on fruit size at harvest tended to be observed when the period of water stress relief (after the deficit period in Stage II) was extended for several weeks, whereas this tendency was minimized when this period lasted no more than 3 weeks. Short recovery periods on deep soils were associated with high psi(stem) values at the end of deficit irrigation periods. On shallow soils, plant water status recovery occurred after one week of full irrigation: water stress management did not therefore represent a problem during Stage II. However, during Postharvest, shallow soils presented the problem of rapidly developing water stress. In such cases, severe stress tends to occur and bloom density and/or fruit set may be substantially reduced in the following season. The possibility of increasing irrigation rates should be considered on shallow soils during postharvest when psi(stem) values become too negative (i.e. <-2.0 MPa) and on deep soils when psi(stem) approaches -1.5 MPa.