K in high concentration in the soil is associated with Mg uptake antagonism. Reduced Mg uptake resulting from excessive K application is a common phenomenon in fruit-tree orchards. Nitrate (NO3-) application usually increases Mg uptake.
The fruit tree species most prone to Mg-deficiency in Chile are apple, pear, quince, orange, lemon and kiwifruit. Differences in susceptibility exist between cultivars of a particular fruit type. In apple, the most susceptible cultivars are 'Golden Delicious' and 'White Winter'. In orange, the 'seedless' cultivars show greater susceptibilty. In grape, 'Thompson Seedless' and 'Torontel', and in avocado, 'Edranol' and 'Zutano', are more prone to deficiency. In pear, 'Beurré Bosc' and 'Asian' more easily become Mg-deficient. In apple, the rootstock used may also affect sensitivity. M-4, M-7, M-9 and MM-106 tend to enhance susceptibility, whereas M-26, M-2 and 'seedling-rootstock' tend to reduce susceptibility.
Mg-deficiency is difficult to rectify. Recovery of fruit trees in response to conventional soil Mg applications is slow, the time to recovery increasing with soil heaviness, alkalinity, or K content. Fertigation lessens the influcence of these restricting factors. Repeated foliar sprays of Mg aid recovery.
Leaf symptoms of Mg-deficiency in 'Granny Smith' apple.
Young 'Red Spur' apple tree affected by Mg-deficiency.
Leaf symptoms of Mg-deficiency of 'Golden Delicious' apple.
Pear leaves showing symptoms of severe Mg-deficiency.
Leaf symptoms of Mg-deficiency in 'Asian' pear.
Leaf symptoms of Mg-deficiency in peach.
Mg-deficiency in a 'D'Agen' prune tree.
Leaf Mg-deficiency symptoms in greenhouse grown 'Mahaleb' cherry rootstock. The nutrient solution applied to the trees was devoid of Mg.
Leaf symptoms of Mg-deficiency in walnut (photo courtesy Rafael Ruiz).
Leaf Mg-deficiency symptoms of 'Torontel' grape.
Symptoms of severe Mg-deficiency in 'Thompson Seedless' grape.
Shoot removed from a Mg-deficient lemon tree.
Avocado leaf showing symptoms of Mg-deficiency and excess chloride (Cl -) uptake (necrosis).
Mg-deficiency symptoms in an avocado branch.
Leaf symptoms of Mg-deficiency in coffee (photo courtesy INPOFOS).
Banana leaf deficient in Mg (photo courtesy CORBANA and INPOFOS).
Leaf symptoms of Mg-deficiency in banana (photo courtesy CORBANA and INPOFOS).