Topic
Urea
About: Urea is a research topic. Over the lifetime, 21394 publications have been published within this topic receiving 382444 citations. The topic is also known as: carbamide & carbonic acid diamide.
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01 Jun 1984TL;DR: In this paper, simulated sheep urine patches in a perennial ryegrass (Lolium perenne L.)/white clover pasture in New Zealand were measured in the field during the summer, autumn and winter periods.
Abstract: Ammonia (NH3) volatilization losses from simulated sheep urine patches in a perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) pasture in New Zealand were measured in the field during the summer, autumn and winter periods. An enclosure technique was used with microplots (23 cm diameter) receiving either sheep urine or aqueous urea at rates equivalent to 500 kg N ha−1 and monitored continuously until measured losses decreased to 0.5% per day. Mean volatilization losses for urine treated plots were 22.2% of the applied N in summer, 24.6% in autumn and 12.2% in winter. Corresponding losses for the urea treated plots were 17.9%, 28.9% and 8.5%. Differences between these two N sources were not significant although the seasonal differences were significant (P ≦ 0.05). Changes in NH3 gas fluxes were found to be related to measured changes in soil pH and air temperature. Two repeated applications of urine or aqueous urea to the same microplot resulted in significantly greater subsequent volatilization losses averaging 29.6% from the second and 37.5% from the third application.
174 citations
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TL;DR: In this article, the uptake of ammonium, nitrate, amino acids and urea was examined in the nitrate-rich Thames estuary and adjacent area in the North Sea during February 1999.
Abstract: The uptake of ammonium, nitrate, amino acids and urea was examined in the nitrate- rich Thames estuary and adjacent area in the North Sea during February 1999. The majority of uptake was by heterotrophic bacteria, as demonstrated by addition of a prokaryotic inhibitor that lowered uptake rates by 82, 66, 49 and 86% for ammonium, nitrate, amino acids and urea, respec- tively. Amino acids were preferred over ammonium and urea, which in turn were preferred over nitrate. Urea was not important as nitrogen substrate. Amino acids were the main nitrogen substrate offshore and at the mouth of the estuary, but in the inner estuary nitrogen was mainly taken up as ammonium and, even more, as nitrate. Nitrate appeared to be the main substrate in the inner estuary (60 to 90%) despite its low affinity for nitrate. The high nitrate uptake by heterotrophic bacteria is probably due to high ambient concentrations of nitrate (up to 650 µM).
174 citations
01 Jan 2007
TL;DR: In this paper, the urease inhibitor NBPT slowed down urea hydrolysis and thus may help decrease ammonia losses in sugarcane fields, but the inhibitor was less effective when rain sufficient to incorporate urea into the soil occurred only 10 to 15 days or latter after fertiliser application.
Abstract: Legal restrictions from burning sugarcane prior to harvest are causing a sharp increase in acreage which is harvested as green cane. The presence of a thick sugarcane trash mulch left after harvest makes it difficult to incorporate fertilisers in the soil. Since large losses of ammonia may occur when urea is surface applied to trash, it is important to find ways to improve urea-N use efficiency. The urease inhibitor NBPT slows down urea hydrolysis and thus may help decrease ammonia losses. Ammonia traps were set up in seven sugarcane fields covered with trash and fertilised with ammonium sulfate or ammonium nitrate, urea, and NBPT-treated urea. All N fertilisers were surface-applied at rates of 80 or 100 kg N ha-1. Very little N was lost when ammonium nitrate or ammonium sulfate were used. However, volatilisation losses as ammonia from the urea treatments varied from 1% (rainy days after fertilisation) to 25% of the applied N. The percentage of reduction in volatilisation due to NBPT application ranged from 15% to 78% depending on the weather conditions during the days following application of N. Addition of NBPT to urea helped to control ammonia losses, but the inhibitor was less effective when rain sufficient to incorporate urea into the soil occurred only 10 to 15 days or latter after fertiliser application.
173 citations
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TL;DR: In this article, Nitrogen-doped titanium dioxide (TiO 2 ) powders were prepared by the heating of titanium hydroxide with urea and showed visible-light photocatalytic activity of about 550nm.
Abstract: Nitrogen-doped titanium dioxide (TiO 2 ) powders were prepared by the heating of titanium hydroxide with urea The samples had a relatively larger specific surface area of 92 ± 2 m 2 g −1 and showed visible-light photocatalytic activity of about 550 nm
173 citations
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172 citations