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Phytotoxicity of foliar-applied urea.
M J Krogmeier1, G W McCarty, J M Bremner
1Department of Agronomy, Iowa State University, Ames, IA 50011.
Summary
Urease inhibitors do not prevent urea-induced leaf necrosis in soybean plants. This damage is caused by excessive urea accumulation, not ammonia formation, highlighting a critical factor in foliar fertilization strategies.
Area of Science:
- Agricultural Science
- Plant Physiology
- Soil Science
Background:
- Urea fertilizer hydrolysis by urease produces ammonia, impacting soil and plant health.
- Foliar urea application can cause leaf-tip necrosis, typically attributed to ammonia toxicity.
Purpose of the Study:
- To investigate if a urease inhibitor, phenylphosphorodiamidate, can prevent urea-induced leaf-tip necrosis in soybean plants.
- To determine the causal agent of leaf-tip necrosis following foliar urea application.
Main Methods:
- Soybean plants were foliar-fertilized with urea, with and without phenylphosphorodiamidate.
- Urea, ammonia content, and urease activity in soybean leaves were analyzed.
- Urea concentrations in necrotic and non-necrotic leaf tissues were compared.
Main Results:
- Phenylphosphorodiamidate addition increased leaf urea content and decreased ammonia levels and urease activity.
- Contrary to expectations, the urease inhibitor exacerbated leaf-tip necrosis.
- Necrotic leaf areas showed significantly higher urea concentrations than healthy tissues.
Conclusions:
- Leaf-tip necrosis from foliar urea application is caused by urea accumulation, not ammonia formation.
- Urease inhibitors are ineffective in preventing this specific type of plant tissue damage.
- Findings necessitate a re-evaluation of urea's role in foliar fertilization phytotoxicity.