The toxicity of banded urea to corn growth and yield as influenced by triple superphosphate

Abstract

Banding of urea in corn (Zea mays L.) production is restricted by toxic conditions from urea hydrolysis, but higher urea rates could reduce application cost. A growth chamber experiment and a field experiment were conducted to study toxicity of banded urea when applied with triple super-phosphate (TSP). In the growth chamber experiment, surface samples from a Ste. Rosalie clay (Humic Gleysol), a Chicot sandy clay loam (Grey-brown Podzol), and an Uplands sandy soil (Humo Ferric, Podzol), were used. The field experiment was conducted on a Ste. Rosalie clay, a St. Bernard loam (Eutric Brunisol), and a Chicot sandy clay loam soil. In the growth chamber experiment, banded urea increased soil pH to 7.2–7.5 at a distance of up to 4 cm from the fertilizer band, and NH3 concentrations were as high as 2.1 mM at 2 cm from the fertilizer band after 20 d. The high pH and NH3 concentrations from urea hydrolysis inhibited corn root and seedling growth. Banding TSP with urea reduced soil pH increases from urea hydrolysis and reduced NH3 concentrations. Root weights increased with added TSP in urea bands. In the field experiment, banding urea at > 40 kg N ha−1 reduced plant density and shoot dry weight in early growth stages. Banding TSP with urea increased seedling growth in all soils. Maximum rates of urea compatible with increased corn yield could be increased from 40 to 80 kg ha−1 when banded with TSP. Key words: Urea, nitrogen, ammonia, triple superphosphate, phosphorus, pH, fertilization, corn (Zea mays L.)