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Phytotoxicity of Banded Urea Amended with Triple Superphosphate and Potassium Chloride

Dep. of Natural Resource Sciences, Macdonald Campus of McGill Univ., 21111 Lakeshore Rd., Ste. Anne de Bellevue, QC, Canada H9X 3V9

^* Corresponding author (afm{at}nrs.mcgill.ca).

Banded urea can result in toxicity to corn (Zea mays L.) germination and growth, due to accumulation of NH₃ and NO^-₂s as a result of urea hydrolysis. Delaying urea hydrolysis through addition of acidic materials may reduce urea toxicity. Laboratory and field experiments were conducted to study phytotoxicity of banded urea amended with triple superphosphate (TSP) or KCI. A Ste. Rosalie clay (fine, mixed, frigid Typic Humaquept), an Ormstown silty clay loam (fine-silty, mixed, frigid Typic Humaquept), and a Chicot sandy clay loam (fineloamy, mixed, frigid Typic Hapludalf) were used in the laboratory to investigate corn germination and growth across distances of 2.0 and 4.0 cm from the fertilizer band with four rates of TSP (0, 0.11, 0.22, and 0.33 g P kg^–1), two rates of KCI (0 and 0.42 g K kg^–1), 0.50 g urea-N kg^–1 and an unfertilized control. Field experiments were conducted on a Ste. Rosalie clay and an Ormstown silty clay loam with two rates of urea (60 and 120 kg N ha^–1) and three rates of TSP (0, 26, and 52 kg P ha^–1), either compacted or blended. In the laboratory experiment, NO^-₂-N, and pH decreased with TSP and KCI, due to delayed urea hydrolysis. Soil electrical conductivity (EC) increased with KCI, but was not affected by TSP. Corn growth decreased with increased soil NH₃ concentration and EC. In the field, corn germination decreased with banded urea and increased with banded TSP at Day 10 after planting, but no difference was found at Day 20. Compacted mixtures of urea-TSP increased corn germination, growth, N uptake, and yield compared with blended mixtures for the same rate of P. Compaction of urea and TSP may provide an effective way to improve efficiency of banded urea for corn production.

Received for publication March 25, 1997.

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