Response of plum trees to deficit irrigation under two crop levels: tree growth, yield and fruit quality

Abstract

The effects of regulated deficit irrigation (RDI) and crop load on Japanese plum were investigated. RDI applied during phase II of fruit growth and post-harvest was compared with irrigation to match full crop evapotranspiration. Each irrigation treatment was thinned to a commercial crop load (described as medium) and to approximately 40% less than the commercial practice (described as low). The RDI strategy allowed for 30% water savings, increasing tree water use efficiency, with minimal effect on crop yield and fruit growth providing that plant water stress during the fruit growth period was low (stem water potential > −1.5 MPa), trees could recover optimum water status well before harvest, and crop load was low. However, the economic return, calculated from fruit weight distribution by commercial categories, was more affected by RDI than yield. The combination of medium crop load and RDI shifted fruit mass distribution towards the low value categories. This lead to similar or even higher economic returns in the RDI treatment with low crop level than with the medium one. In addition, since both, low crop level and RDI, increased fruit total soluble solids (TSS) concentration, fruit under RDI and low crop levels had the highest values of TSS.