RATE OF HYDROLYSIS AND NITRIFICATION OF UREA AND IMPLICATIONS OF ITS USE IN POTATO PRODUCTION

The effect of soil temperature on urea hydrolysis and subsequent nitrification in an acid Podzolic soil was investigated under laboratory conditions to determine the transformation rate parameters. More than 90% of applied urea was hydrolyzed within 5 d at temperatures between 9 and 18 °C. Subsequent nitrification rates were more temperature dependent and increased from 4 up to 18 °C. Nitrification was limited at 4 °C, was extensive at 9 °C, and it was essentially complete after 48–68 d at 18 °C and 90% complete after 92 d at 9 and 13 °C. The nitrate-N produced during the cropping season from a spring application of urea was predicted, with a model based on the laboratory determined transformation rates, for field conditions at normal soil temperatures. Following spring-applied urea (20 May), the model indicated that nitrification would be virtually complete by 31 July. In a field experiment, total N uptake by Kennebec potatoes (Solanum tuberosum L.) from applied ammonium nitrate was 95% complete within t...