MOVEMENT OF UREA AND ITS HYDROLYSIS PRODUCTS AS INFLUENCED BY MOISTURE-CONTENT AND UREASE INHIBITORS

A laboratory experiment was conducted on an Aquic Udifluvent Belgian s oil in order to study the movement of urea and its hydrolysis products . This study was carried out at two moisture levels (10 and 20%) upon the addition of three types of urease inhibitors: hydroquinone, phenyl phosphorodiamidate (PPDA), and N-(n-butyl)phosphorothioic triamide (NB PT). The results clearly show the effects of the inhibitors in retardi ng the hydrolysis of urea. The highest effect was observed with NBPT, followed by hydroquinone, and PPDA. The effect was more pronounced at 10% than at 20% moisture content. It was clear that subsequent nitrifi cation of the NH;: formed was inhibited at the lower moisture level. A t 10% moisture, from the 7th day of incubation on, some NH4+ moved abo ut 3 cm and reached the top of the soil column. At 20% moisture, no NH 4+ reached the surface as it was quickly nitrified. After 17 days of i ncubation and at 20% moisture, the total mineral N was more or less ho mogeneously distributed within the soil column. In contrast, at 10% mo isture, the remaining urea and the hydrolysis products were still conc entrated at the place of application. The distribution of urea and its hydrolysis products was comparable with 7 days of incubation at 20% m oisture and 17 days at 10%.