Deficit irrigation without reducing yield or nut splitting in pistachio (Pistacia vera cv Kerman on Pistacia terebinthus L.)

摘要

An irrigation experiment involving pistachio (Pistacia vera cv Kerman on Pistacia terebinthus L.rootstocks) was performed over a four-year period in central Spain to determine the effect ofregulated deficit irrigation (RDI) on nut yield and quality. The growth season was dividedinto three phenological stages: stage I – from sprouting until the end of rapid nut growth;stage II – from maximum nut size until the beginning of kernel growth; and stage III – fromthe beginning of kernel growth until harvest. Control trees were irrigated to supply their fullwater needs throughout the growth season, except for the post-harvest period. Sustaineddeficit irrigation at 65% (DI65) and 50% (DI50) of control irrigation was provided to two othergroups of trees. The RDI provided to a further group was designed to provide a stress periodduring stages I and II but no water stress during stage III; the aim was to reduce water useand increase the percentage of split nuts. A fifth group of trees was maintained under rainfed conditions. Water potential and leaf conductance were affected in the DI65, DI50 and rainfed treatments mainly during stages II and III, with midday water potentials below 2.0 MPa.The RDI trees were only significantly water stressed during stage II, showing midday waterpotentials of around 1.4 MPa. On most days, leaf conductance was not significantlyaffected in any of the irrigation treatments. The nuts of the DI65 and DI50 trees were smallerin diameter and their total yield was reduced compared to the controls. However, nosignificant differences in kernel dry weight were observed. The RDI trees showed a totalyield and percentage of split nuts similar to those of the controls, even though they receivedaround 20% less water. The split nut yield showed a linear relationship with crop evapotranspiration.However, since the percentage of split nuts was similar in all treatments thisvariation was likely related to the total yield. The RDI trees did not show the normalalternate bearing pattern (which was clearly maintained in the control trees). Early splitting,a process that decreases the quality of the yield, was not related to water status but totemperatures lower than 13 8C. The results suggest that P. terebinthus L. rootstocks confer P.vera scions a degree of drought-resistance, reducing the likelihood of water stress and,therefore, allowing more severe RDI scheduling.