Avoid Ammonium Toxicity

March 2021

Different factors, including cold weather and low soil temperatures can impact optimal tomato planting and establishment. We are seeing cold soils which could present challenging conditions to get the crops off to a quick and healthy start.

One common issue we should be aware of under the current growing conditions (low temperatures, wet or low oxygen soils) is ammonium toxicity. Ammonium toxicity occurs when there is too much ammonium available for plant uptake in the soil and plants absorb harmful amounts of it. Remember that the preferred form of nitrogen for plant uptake is nitrate and the conversion of urea and ammonium into nitrate nitrogen in the soil is a biological process governed by temperature, moisture and soil pH.


Ammonium toxicity affects most plants but the threshold at which symptoms of toxicity show differs among plant species. The most sensitive plants include tomatoes, potatoes, strawberries, lettuces, brassicas and some citrus species. The symptoms of ammonium toxicity include chlorosis of leaves, decreased growth and poor root development. Depending on plant species, the edge of leaves may curl upward or downward. Some plants may die and the marketability of surviving plants is reduced. Also, seed germination and seedling establishment can be inhibited by ammonium toxicity.

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Symptoms of ammonium toxicity in tomatoes.
Photograph by Cary Peters as seen on Culture Notes by Neil Mattson, Cornell University.

Ammonium toxicity can be prevented by following appropriate cultural practices. When it comes to choosing your spring nitrogen fertilizer, the use of ammonium containing fertilizers or fertilizers that are converted to ammonium (urea) can have a negative impact on crops due to toxicity from ammonium. Manures can also release ammonium. By reducing the amount of nitrogen in the ammonium form and using a nitrate nitrogen fertilizer we can avoid ammonium toxicity. There is clear evidence from trials that better root growth is attained when plants receive nitrate nitrogen.

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Tomato roots
REF.: Research Centre Hanninghof, Yara - 2004


Improved root growth in citrus trees fertilized with YaraLiva CALCINIT
Quaggio et al., unpublished data

Nitrate is immediately plant available and it can be easily taken up by crops. Field research confirms that using nitrate-nitrogen can significantly increase yields compared to using ammonium nitrogen. Also, nitrate nitrogen promotes uptake of critical nutrients such as calcium, magnesium, and potassium, increasing crop quality.

Provide your Crop with the Best Nitrate Product Options


YaraLiva Calcium Nitrate fertilizers provide fast-acting nitrate nitrogen, along with strength-building calcium. In combination, these nutrients fuel prolonged growth and are the preferred choice to prevent the incidence of ammonium toxicity.


YaraTera NITRAKAL provides a balanced formulation of nitrate-nitrogen, potassium and calcium immediately available for the crop that maintains an optimum root environment for healthy early growth and improved tolerance to diseases and environmental stress.

Contact your local Yara representative to find YaraLiva and YaraTera distributors near you.

Read the latest tomato crop nutrition advice

sebastian korob
Sebastian Korob
Crop Manager, Vegetable/Berries