Effects of limestone amendments in the response of holm oak infected by Phytophthora cinnamomi

Abstract: The aim of this work was to evaluate the effects of two limestone amendments in the response of infected holm oaks in field conditions. An experiment with different types of limestone amendments (CaCO3 and CaSO4) was carried out in two dehesas farms – open oak woodland – with oak root rot caused by Phytophthora cinnamomi in Huelva province (Andalusia, Spain). We evaluated the change of soil parameters (pH, exchangeable Ca and K), water and nutrient concentrations of holm oak leaves, shoot growth and the evolution of tree canopy defoliation. Limestone amendments have effectively increased the concentration of soil exchangeable Ca, especially with CaCO3 application. The increase of Ca in soil has shifted exchangeable K. In the short term, CaCO3 amendment increased soil pH while CaSO4 reduced it. Tree shoot growth was similar between limestone amendments and did not differ to the control trees. Additionally, no significant differences in nutrient concentrations of leaves were found. CaCO3 amendment increased the water concentration of leaves. Compared with control trees, limestone amendments slowed down the defoliation of the canopy in the first year after treatment but kept increasing the second year. Results obtained indicate that limestone amendments may attenuate the disease symptoms but their effects are ephemeral and are related to weather condition.