Transformations and losses of urea nitrogen after application to flooded rice

Abstract

Direct measurements of gaseous loss, 15N labelling and intensive sampling of floodwater and soil columns were used to follow the transformations and movement of fertilizer nitrogen (N) applied as urea (80 kg N ha-1) into the floodwater of a young rice crop. During the first 11 days after urea application, about 46% of the applied N was lost from the water-soil-plant system. Only 11% was volatilized as ammonia, despite very high floodwater pH values (up to pH 10) and some strong winds. Gaseous loss as nitrous oxide and leaching of N beyond a soil depth of 100 mm were both negligible. All the evidence indicates that the other 35% of the applied N was lost as dinitrogen produced by denitrification of nitrite and nitrate after nitrification of ammonium near the soil surface. No further losses from the system were detected after the first 11 days. Final recovery of the fertilizer N by the above-ground crop was only 17%. The results show that the several processes which resulted in gaseous loss of N operated concurrently, commencing almost immediately after fertilizer application. The major microbiological transformations appeared to occur near the soil-water interface (c. 0-20 mm depth).

Soil quality assessment and phytoaccumulation potentials of selected edible vegetables around Ntigha solid waste dump, Abia State, Nigeria

“…This could explain its higher activities in 0-45cm depth than 46-90cm depth in the present study (Fig.9). It has been noted that the activity of hydrogen peroxidase is high in acidic environment [32]. This is in line with the observation made on hydrogen peroxidase in this study.…”

Dynamics of ammonia volatilization losses in wetland soil following the broadcasting application of urea amended with phenyl phosphorodiamedate

“…It is assumed that gases other than ammonia may have contributed to a significant part of the total gaseous loss from urea in the floodwater or in the aerobic surface of the flooded soil. Although previous investigations have demonstrated that of nitrous oxide contributed very little to the N losses in flooded soils (FRENEY et al 1981 ;SMITH et al 1982;SIMPSON et al 1984), there was direct evidence that about 46~ of the applied urea was lost from the flooded rice-soil system, 35~/o being lost as dinitrogen (N2) with only 11~ being volatilized as ammonia (SIMPSON et al 1984).…”

“…Urea largely remained nonhydrolyzed in the floodwater which exhibited a low urease activity (VLEK et al 1980). Since the major site of urea hydrolysis activity is lower in floodwater than in the underlying soil surface (DELAUNE and PATRICK 1970;VLEK et al 1980;SIMPSON et aL 1984), this may have resulted in the persistence of large amounts of nonhydrolyzed urea in the floodwater of the urea + PPD treatment. The inhibition of urea hydrolysis in the floodwater after the broadcasting of urea with PPD in the present study took a longer time than in similar greenhouse experiments reported by other workers (VLEK et al 1980;BYRNES et aL 1983).…”

Nitrogen gas (N2+N2O) flux from urea applied to lowland rice as affected by green manure

“…Other studies (Simpson et al, 1984;Smith et al, 1982) have also reported an increase in floodwater (nitrate + nitrite)-N following broadcast application of urea to flooded rice. Simpson et al (1984) observed a maximum floodwater (nitrate + nitrite)-N concentration of 2.5 g N m ~ during the 11 days following urea application in Australia.…”