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Ammonia/Ammonium fertilizers induce specific root toxicity symptoms

Careful fertilizer management is required to avoid seedling damage from the release of potentially toxic nitrogen forms from inorganic and organic fertilizers. 

In the November–December 2016 issue of Agronomy Journal, researchers report on controlled studies of seedling responses to fertilizer source, placement, and rate. Using digital scanners embedded in soil, the research team was able to capture high-resolution, time lapse images of symptoms induced by ammonia/ ammonium in the fertilizer toxicity zone. 

The team observed that roots of three species were damaged several centimeters from the fertilizer band where ammonia gas and ammonium ions are transported. Urea pellets and chicken manure induced more symptoms than polycoated urea and compost. Symptoms include necrotic meristems, root shrinkage, root hair death, and accelerated lateral rooting, sometimes causing seedling death.

Close up view of root tip

Species-specific root architecture matters. No-till wheat producers have been placing ammoniacal fertilizers below or near the seed for more than 30 years. This study demonstrated that the multi-seminal axes of wheat provide insurance against main root fatalities, thereby increasing seedling survival. That planting system applied to taprooted crops like canola can be much more devastating. Wheat farmers will need to rethink drill designs and 4R (right source, rate, time, and place) nitrogen management when diversifying their rotations with tap-rooted crops.

Read the open access paper in Agronomy Journal