Role in the plant: Used in actively growing plants to produce chlorophyll (green pigmentation) and plant protein. Often required in high quantities if the plant is not a legume or unable to fix its own nitrogen.
Deficiency symptoms: Pale yellowing in the lower/older leaves of the crops. In cabbages, this may be identified as red discolouration of the leaves.
Toxicity symptoms: Over fertilized soils can result in crop lodging, soft leaves that are susceptible to disease and poor seed development. Under dry conditions root burn from soil-applied fertilizers can result in stunting of the crop and wilting. Foliar toxicities can result in (phytotoxicities) burning of the leaves.
Soils that have nitrogen most prevalent: Carry out soil analysis. Soils with high clay or organic matter concentrations are most likely to have higher levels of Nitrogen then those that are sandy with low levels of organic matter. Crop rotations that used legumes will increase the nitrogen levels in the soils for the following season.
Management remarks: Avoid nitrogen applications through the leaves or soil when the crop is moisture stressed. On sandy soils split nitrogen applications throughout the season. Avoid nitrogen applications on Soyas and other legumes that are able to fix their own nitrogen.