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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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Journal ArticleDOI
TL;DR: The present model predicted that 95% of the label movements across the GIT could be accommodated by three or fewer entries and returns of urea-N and 99% by recycling for a maximum of six occasions, and offered a relatively simple means of estimating anabolic reuse of Urea by digestive tract micro-organisms.
Abstract: The effect of intake on urea production, entry into the digestive tract and return of N to the ornithine cycle was studied in four sheep. Each sheep received 0–6, 1–2 and 1.8 × estimated maintenance energy intake quantities of grass pellets for 9 d. After 4 d of adjustment, N balance measurements were conducted between days 5 and 8. From day 7 to day 9 animals were continuously infused, via the jugular vein, with [15N15N]urea and three urine samples were collected at approximately 2h intervals 48–54h after the start of infusion. Total urea and enrichments of [15N15N]- and [14N15N]urea in the urine samples were determined. Urea production was calculated from the isotopic dilution of [15N15N]urea and entry into the gastrointestinal tract (GIT) obtained from the difference between this and urinary urea elimination. Urea which enters the GIT undergoes hydrolysis to liberate NH3 which may be reabsorbed and enter the ornithine cycle, in which case the product is [14N15N]urea, based on the probabilities of labelled and unlabelled N providing ureagenic precursors. The quantity of urea-N which returns to the ornithine cycle from the GIT can thus be calculated. Existing models based on this approach yield overestimates of the fate of individual urea molecules due to a failure to allow for multiple recycling of [14N15N]urea species through the GIT. Refinements introduced to cover this resulted in a 33–48 % reduction in calculated return of label for the current study. The present model also predicted that 95 % of the label movements across the GIT could be accommodated by three or fewer entries and returns of urea-N and 99 % by recycling for a maximum of six occasions. Urea-N production increased with intake (P < 0.001) and exceeded digestible N values at all intakes. Urea which entered the digestive tract, both in absolute terms (P < 0.001) and as a proportion of production (0.62, 0.69, 0.73; P = 0.027), increased with intake. The proportion of entry into the digestive tract which was returned to the ornithine cycle remained reasonably constant (0.37–0.41) across all intakes but the absolute amount increased (5.6, 9.2 and 15.0gN/d; P < 0.001) with intake. If allowance is included for losses of 15N in faeces then the approach offers a relatively simple means of estimating anabolic reuse of urea by digestive tract micro-organisms and can complement data obtained from the technically more demanding arterio-venous and multiple-isotope techniques used hitherto.Urea: Gastrointestinal tract: [15N]kinetics: Sheep

96 citations

Journal ArticleDOI
TL;DR: At times urea was safe but in one experiment heavy dressings incorporated in the seed-bed caused serious damage and here again there is an indication of the infrequent slightly lower efficiency of urea.
Abstract: The results of the grassland experiments show that as a straight nitrogen fertilizer urea was, on average, slightly less effective than the conventional materials. In the majority of individual experiments there was no significant difference between the yields from urea and those from ‘Nitro-Chalk’; on the other hand, in a very few experiments the urea yields were much lower. The arithmetic means of the averages in each series of grassland experiments indicate that urea gave total yields about 93% of those from ‘Nitro-Chalk’ and the average response (i.e. difference from control) from urea was about 85% of that from ‘Nitro-Chalk’.The available data for cereals are considerably less than for grassland but here again there is an indication of the infrequent slightly lower efficiency of urea.On kale the results are confusing. At times urea was safe but in one experiment heavy dressings incorporated in the seed-bed caused serious damage.

96 citations

Journal ArticleDOI
01 Oct 1985
TL;DR: In this paper, two modified urea products (urea supergranules [USG] and sulfur-coated urea [SCU]) were compared with conventional urea and ammonium sulfate as sources of nitrogen (N), applied at 58 kg N ha−1 and 116 kg N h−1, for lowland rice grown in an alkaline soil of low organic matter and light texture (Typic Ustipsamment).
Abstract: Two modified urea products (urea supergranules [USG] and sulfur-coated urea [SCU]) were compared with conventional urea and ammonium sulfate as sources of nitrogen (N), applied at 58 kg N ha−1 and 116 kg N ha−1, for lowland rice grown in an alkaline soil of low organic matter and light texture (Typic Ustipsamment) having a water percolation rate of 109 mm day−1. The SCU and USG were applied at transplanting, and the whole dose of nitrogen was15N-labeled; the SCU was prepared in the laboratory and was not completely representative of commercial SCU. The SCU was broadcast and incorporated, whereas the USG was point-placed at a depth of 7–8 cm. The urea and ammonium sulfate applications were split: two-thirds was broadcast and incorporated at transplanting, and one-third was broadcast at panicle initiation. All fertilizers except the last one-third of the urea and ammonium sulfate were labeled with15N so that a fertilizer-N balance at flowering and maturity stages of the crop could be constructed and the magnitude of N loss assessed. At all harvests and N rates, rice recovered more15N from SCU than from the other sources. At maturity, the crop recovered 38 to 42% of the15N from SCU and only 23 to 31% of the15N from the conventional fertilizers, urea and ammonium sulfate, whose recovery rates were not significantly different. In contrast, less than 9% of the USG-N was utilized. Fertilizer nitrogen uptake was directly related to the yield response from the different sources. Most of the fertilizer N was taken up by the time the plants were flowering although recovery did increase up to maturity in some treatments. Analysis of the soil plus roots revealed that less than 1% of the added15N was in the mineral form. Between 20 and 30% of the15N applied as urea, SCU, and ammonium sulfate was recovered in the soil plus roots, mainly in the 0–15 cm soil layer. Only 16% of the15N applied as USG was recovered in the soil, and this15N was distributed throughout the soil profile to a depth of 70 cm, which was the lowest depth of sampling. Calculations of the15N balance showed that 46 to 50% of the urea and ammonium sulfate was unaccounted for and considered lost from the system. Only 27 to 38% of the15N applied as SCU was not recovered at maturity, but 78% of the USG application was unaccounted for. The extensive losses and poor plant recovery of USG at this site are discussed in relation to the high percolation rate, which is atypical of many ricegrowing areas.

96 citations

Journal ArticleDOI
TL;DR: Urea-based vinyl monomers synthesized and investigated for their ability to function as polymerizable hosts for the molecular imprinting of N-Z-D- or L-glutamic acid in polar media (DMSO or DMF) showed high affinity for benzoate, reflected in liquid chromatography retention data.
Abstract: A series of urea-based vinyl monomers was synthesized and investigated for their ability to function as polymerizable hosts for the molecular imprinting of N-Z-d- or l-glutamic acid in polar media (DMSO or DMF). The monomers were synthesized in one step from a polymerizable isocyanate and a nonpolymerizable amine or vice versa, with yields typically over 70%. Prior to polymerization their solution binding properties vis-a-vis tetrabutylammonium benzoate in DMSO were investigated by 1H NMR, UV−vis and fluorescence monitored titrations. The affinities of the urea monomers for benzoate depended upon the substitution pattern of the urea, with all diaryl ureas exhibiting high affinity. EDMA-based imprinted polymers prepared in DMF or DMSO against Z-d-(or l)-glutamic acid using 2 equiv of the urea monomer and 2 equiv of base were able to recognize the imprinted dianion as well as larger molecules containing the glutamic acid substructure. The affinity, reflected in liquid chromatography retention data, correlat...

96 citations

Journal ArticleDOI
TL;DR: Turbidity values are in agreement, indicating that cross-linking of casein micelles with transglutaminase results in a covalently bound protein network, which is entirely stable to disruption by urea and/or citrate.

96 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,000
20221,982
2021433
2020502
2019589
2018557