N-deficiency is first indicated by a slight reduction in green colour intensity of the leaves. If N becomes increasingly deficient, intensity decreases. If extreme, the entire leaf, including the veins, becomes yellow. Yellowing of the old leaves precedes that of the younger leaves due to N-extration by the old leaves. In many species reduced green colouration is accompanied by orange or reddish pigmentation of the entire leaf or parts thereof. This typically occurs in peach, apple, pear and cherry. On occasions the stems also become red. In lemon, N-deficiency may be noted by the sudden incidence of vein yellowing in mature leaves. N-deficiency may also effect a reduction in leaf size.
Images from the book Symptons of Nutrient Imbalances in fruit trees, Bruno Razeto.
'Granny Smith' apple leaves: Left- leaf from a N-deficient tree. Right- leaf from a non-N-deficient tree.
'Red Delicious' apple trees: Front- tree with severe N-deficiency. Back- trees having received soil-applied N fertilizer.
'Granny Smith' apples: Left- harvested from a healthy tree. Right- harvested from a N-deficient tree.
Peach leaves: Left- N-deficient leaf. Right- normal leaf concerning N status.
Left- N-fertilized peach tree in a highly N-deficient orchard.
Symptoms of severe N-deficiency in peach shoots developing in spring.
Grape leaves: Right- leaf with symptoms of N-deficiency.
Grape shoots: Left- normal shoot concerning N status. Right- N-deficient shoot.
Lemon leaves: Left- N-deficient leaf. Right- normal leaf concerning N-status.
Severe N-deficiency in lemon.
Avocado leaves: Left- N-deficient leaf. Center- leaf low in N. Right- normal leaf concerning N status.
Avocado nursery: Front- plants growing in a substrate devoid of N. Back- plants having been supplied with N fertilizer.
Mango tree deficient in N.
Symptoms of N-deficiency in coffee ('Arabica') (Photo courtesy INPOFOS).
Sections of a banana leaf: Left- leaf section from a N-deficient plant. Right- leaf section from a normal plant concerning N-status.
Front- strawberry plant growing in a N-deficient substrate. Back- strawberry plants having been fertilized with N.