Phytotoxicity of foliar-applied urea.

Recent work in our laboratory showed that the adverse effect of urea fertilizer on seed germination and seedling growth in soil is due to ammonia produced through hydrolysis of urea by soil urease (NH(2)CONH(2) + H(2)O --> 2NH(3) + CO(2)) and can be eliminated by amending the fertilizer with a small amount of a urease inhibitor such as phenylphosphorodiamidate. Because the leaf-tip necrosis often observed after foliar fertilization of plants with urea is usually attributed to ammonia formed through hydrolysis of urea by plant urease, we studied the possibility that this necrosis could be eliminated or reduced by adding phenylphosphorodiamidate to the urea fertilizer. We found that, although addition of this urease inhibitor to foliar-applied urea increased the urea content and decreased the ammonia content and urease activity of soybean [Glycine max.

Evidence that the adverse effect of urea fertilizer on seed germination in soil is due to ammonia formed through hydrolysis of urea by soil urease.

Studies using seeds of wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.

Potential phytotoxicity associated with the use of soil urease inhibitors.

Recent work in our laboratory showed that the adverse effect of urea fertilizer on seed germination and seedling growth in soil is due to ammonia produced through hydrolysis of urea by soil urease (NH(2)CONH(2) + H(2)O --> 2NH(3) + CO(2)) and can be eliminated by amending the fertilizer with a small amount of a urease inhibitor such as N-(n-butyl)thiophosphoric triamide or phenylphosphorodiamidate. Continuation of this work showed that these inhibitors can induce leaf-tip necrosis in plants. Research to account for this phytotoxicity indicated that it resulted from an accumulation of toxic amounts of urea in plants through inhibition of urease activity by N-(n-butyl)thiophosphoric triamide and phenylphosphorodiamidate.

Elimination of the adverse effects of urea fertilizer on seed germination, seedling growth, and early plant growth in soil.

The rapidly increasing importance of urea fertilizer in world agriculture has stimulated research to find methods of reducing the problems associated with the use of this fertilizer. One of these problems is that urea has adverse effects on seed germination, seedling growth, and early plant growth in soil. Because there is evidence that these adverse effects are caused largely, if not entirely, by ammonia produced through hydrolysis of urea fertilizer by soil urease, we explored the possibility that they could be reduced or eliminated by amending urea fertilizer with a small amount of a urease inhibitor.