NITRITE ACCUMULATION AND DENITRIFICATION DURING UREA HYDROLYSIS WITH ADDED TRIPLE SUPERPHOSPHATE

Banded urea could cause nitrite (NO2-) accumulation and enhanced denit rification due to ammonia (NH,) toxicity to Nitrobacter. Delayed urea hydrolysis with addition of acidic phosphate to urea would reduce thes e problems. A laboratory experiment was conducted to evaluate effects of triple superphosphate (TSP) on NO, accumulation and denitrification . A Ste. Rosalie clay (Typic Humaquept), an Ormstown silty clay loam ( Typic Humaquept) and a Chicot sandy clay loam (Typic Hapludalf) were u sed. Treatments included three rates of TSP (0, 0.22, and 0.44 g P col umn(-1)) and 0.50 g N column(-1) with an unfertilized control. Urea an d TSP were pelleted and placed on soil columns which were sampled for urea, ammonium (NH4+), NH3, nitrate (NO3-), NO2--N, and pH analyses. D enitrification was measured on day 7, 14, and 21. Soil pH and NH, conc entrations were reduced with added TSP due to delayed urea hydrolysis, and as a result, NO2- accumulation and denitrification were decreased . With time, differences in denitrification rate decreased between tre atments with urea alone and with urea plus TSP, implying that TSP was more effective in the early stages of urea hydrolysis. Application of TSP with urea may improve urea use efficiency through reduced denitrif ication.