Ammonium nitrogen accumulation and root injury to tomato plants

Soluble fertilisers applied at rates commonly used in commercial tomato glass‐houses can cause root injury which may result in obvious external symptoms or which may be reflected only in reduced or delayed yields or difficulty in fruit setting. Although the rates of application may be safe initially, accumulation of ammonium salts or of soluble salts in general may reach damaging levels for one or more of several reasons. In a trial with varied rates of soluble fertiliser feeding, yield was highest with lowest fertiliser application rates, while root rot and corkiness were greatest with highest rates. In an investigation of the relation of ammonium accumulation to root injury, it was found that vegetative growth and early yields were reduced in plots where ammonium accumulation occurred due to lack of nitrification in fumigated soils fertilised with urea. Root rot and corkiness were markedly more severe in these fumigated plots than III non‐fumigated check plots. Root symptoms were similar to those shown elsewhere to be due to fungus attack. Thus in the root rot complex, a common set of symptoms may result from several different causes acting alone or in combination.