Water retention potentials of Italian soils and physiological responses of potted golden kiwifruit

Correct water management of golden kiwifruit vines, besides being essential for reaching high yield and fruit quality, is also fundamental to keep plants healthy and avoid useless water loss. The objectives of this trial were to: 1) assess the water retention curve in typical soils for the kiwifruit production in Italy; 2) evaluate the response of potted Zezy002 plants to the variation of soil moisture, in term of leaf gas exchange and stem water potential. Plants grown on each soil were divided into two groups: 3 plants were irrigated maintaining soil water at field capacity (control); 4 plants were subjected to water stress as follows: irrigation rate was reduced 50 % of the evapotranspiration rate for one week, then irrigation was suspended. Two days after water suspension, 2 of the 4 stressed plants were irrigated as for the control plants (recovery), the other 2 vines were not irrigated (stress). Each pot was provided with a chalk potentiometric probe so that soil matric potential was constantly monitored. During the experiment leaf gas exchange and stem water potential were daily measured. After irrigation stop, a decrease of net photosynthesis, transpiration and stomatal conductance were observed, on the other hand, intercellular CO2 concentration showed the opposite trend. Specific behavior has been detected for the two loam soils tested (here labelled as "sand-clay-silt" and "silt" soils). At wilting point, established when plant photosynthetic activity stopped, soil matric potential, measured by chalk probes, ranged between -1.8 and -2.0 MPa in all soils with the exception of "sandy-clay-silt", where it was -0.49 MPa. Soil matric potential at field water capacity ranged between -20 and -50 kPa in all soils with the exception of "silt" soil (-140 kPa). This peculiar behavior will be likely due to specific pore size distribution or poor-connected pores, however further investigations are needed.