Phytotoxicity of banded urea amended with triple superphosphate and potassium chloride

Banded urea can result in toxicity to corn (Zea mays L.) germination and gr owth, due to accumulation of NH3 and NO2- as a result of urea hydrolysis. D elaying urea hydrolysis through addition of acidic materials may reduce ure a toxicity. Laboratory and field experiments were conducted to studs phyoto xicity of banded urea amended with triple superphosphate (TSP) or KCl. A St e. Rosalie clay (fine, mixed, frigid Typic Humaquept), on Ormstown silty cl ay loam (fine-silty, mixed, frigid Typic Humaquept), and a Chicot sandy cla y loam (fine-loamy, mixed, frigid Typic Hapludalf) were used in the laborat ory 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 KCl (0 and 0.42 g K kg(-1)), 0.50 g urea-N k g(-1) and an unfertilized control. Field experiments were conducted on a St e, Rosalie clay and an Ormstown silty clay Loom 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)), ei ther compacted or blended. In the laboratory experiment, NH3, NO2-, and pH decreased with TSP and KCl, due to delayed urea hydrolysis. Soil electrical conductivity (EC) increased with KCl, but was not affected by TSP. Corn gr owth decreased with increased soil NH3 concentration and EC. In the field, corn germination decreased with banded urea and increased with banded TSP a t Day 10 after planting, but no difference was found at Day 20. Compacted m ixtures 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 f or corn production.