Influence of irrigation strategies on productivity, fruit quality and soil-plant water status of subsurface drip-irrigated apple trees

Introduction. The aim of this work was to study the effects of regulated deficit irrigation (RDI) on fruit yield, fruit weight and fruit quality parameters, as well as soil-plant water relations, in apple orchards under high frequency subsurface drip irrigation in a region with a continental climate. Materials and methods. Four irrigation treatments were applied in 2010 and 2011 to apple trees cv. 'Gala':T1, no irrigation; T2, optimal irrigation except during summer; T3, optimal irrigation except during summer when RDI with a threshold for irrigation at -1.2 MPa midday stem water potential (Psi stem) was utilised; T4, optimal irrigation. The soil water status and plant water status were followed over two growing seasons. Results and discussion. The irrigation treatments had no significant impact on fruit yield. However, compared with optimal irrigation (T4) and RDI (T3), the absence of irrigation in summer (T1, T2) induced low Psi stem (< -1.2 MPa), decreased fruit size and slightly increased the soluble solid, vitamin C and polyphenol contents of the fruits. The RDI (T3) during summer allowed a water-use reduction of 47% without loss in fruit yield, fruit weight and fruit quality compared with the optimal irrigation (T4). Conclusion. The RDI treatment saved 47% water compared with optimal irrigation without negative impacts on yield and fruit quality. In the temperate conditions of Switzerland, Psi stem, as well as Psi soil, are well adapted for scheduling RDI in apple orchards.