Ca and Mg nutrition and its application in Eucalyptus and Pinus plantations

Our objective with this review was to understand the possible benefits and opportunities of Ca and Mg applications in plantation forests through lime, gypsum or other base cation rich materials, with a specific focus on highly productive, short rotation Eucalyptus and Pinus plantations. We started by identifying the Ca and Mg demand by these forest plantations and the efficiency of absorption, use and cycling of these nutrients in some species of each genus. We subsequently grouped the main hypothesis and evidence to explain the mechanisms developed by these species to tolerate acidic soil conditions. We also grouped research that related the response to Ca and Mg application in such plantations and we tried to establish relationship with the product and rate used and considering the soil properties. We found that despite the high tolerance to acidic soils, specifically to Al toxicity, some species of both genera demand large quantities of Ca and Mg to reach high levels of productivity. The tolerance mechanism to acidic soils appears to come at a cost of carbohydrate allocation which may explain the modest reductions of stand volume growth that have been reported. In base-poor soils, we found a strong relationship between the Ca and Mg exchangeable in the soil and the response to Ca and Mg application, indicating that higher responses are found when the Ca and Mg availability is lower than 4 and 2 mmol(c) L-1 respectively. We conclude that the main benefit of lime application in these forests is increase the Ca and Mg availability and not to increase the soil pH or to lower acid saturation. Liming to increase the soil pH can be important only in soils with very high or toxic levels of solubilized Mn, since species of both genera seem to have only a limited ability to avoid the uptake of this nutrient when present in high concentrations in the soil solution.