Nitrogen
Nitrogen is necessary for many tree functions, including growth, fruit bud formation, fruit set and fruit size. Because of the complexity of nitrogen interactions with quality and production, the best guide for nitrogen rates is leaf analysis.
Identification
- Usually first appears on older leaves,
- Leaves turn light green or yellow as nitrogen is relocated from older, less productive leaves to the newest growth,
- The bark of shoots and twigs may become reddish in colour and shoot growth is spindly,
- If the deficiency is prolonged, older leaves become orange to reddish in colour and may drop prematurely,
- Fruit bud formation and fruit set may be restricted,
- Fruit is small and highly coloured and yields will be reduced.
- Terminal shoot growth of less than 20 cm on bearing trees and less than 40 cm on non-bearing trees may indicate a nitrogen deficiency.
Often Confused With
Chemical:
- spray damage yellowing and browning of leaf margins and interveinal areas,
- herbicides such as triazines (simazine, atrazine); ureas (diuron, linuron), uracil (terbacil, bromacil); dichlobenil, amitrole.
Diseases:
- canker diseases along trunks and branches,
- anthracnose,
- leaf blotch.
Insects:
- aphids,
- leafhoppers,
- mites,
- plant bugs,
- wood boring insects,
- root feeders.
Mechanical:
- damage to tree bark,
- leaf scorch,
- root injury,
- ozone.
Soil & planting conditions:
- decomposition of organic materials with high carbon/nitrogen (C/N) ratios,
- leaching of nitrates from sandy soils or soils with low organic matter,
- waterlogged soil conditions,
- dry soil conditions,
- soil compaction,
- weed competition,
- too little fertilizer applied.
Weather:
- low temperatures and frost.
Scouting Notes
Cool growing conditions in early spring often cause plants to develop a temporary nitrogen deficiency. This is usually due to poor growing conditions, and not necessarily a lack of nitrogen in the soil. Nitrogen deficiency often occurs when a permanent grass is seeded in the orchard or when a large amount of organic matter which is low in nitrogen, such as straw, is worked in to the soil. Deficiency symptoms may also occur when fertilizer is leached by heavy rains.
