15N Balance Research Articles

Agronomic Evaluation of New Ureaforms for Flooded Rice

AbstractRice (Oryza sativa L.) seldom utilizes more than 20 to 40% of the applied urea. Inefficient N utilization is largely attributed to N loss through ammonia (NH3) volatilization and denitrification. Increased N efficiency can be obtained with a slow‐release fertilizer such as ureaform (UF), which is the condensation product of urea and formaldehyde. A recent development in the production process of UF utilizes paraformaldehyde (PFA) addition to urea, which produces a modified urea fertilizer containing unreacted urea and methylene urea polymers. The purpose of this study was to evaluate N uptake and yield response of flooded rice and to determine NH3 volatilization losses from applications of 15N urea, UF, and methylenediurea. The UF fertilizers evaluated had PFA additions to urea ranging from 0% (urea) to 15% (UF‐15). In a greenhouse study with flooded rice, N uptake was measured and apparent N losses were estimated from an 15N balance. Direct NH3 volatilization losses were measured in a forced‐draft volatilization system. There was an increase in N uptake and a reduction in apparent and measured N losses from the modified urea fertilizers as the proportion of PFA increased. Plant 15N uptake at maturity can be expressed by the quadriatic equation: % recovery in total plant = 18.53 + 1.10%PFA − 0.02%PFA2. Total 15N recovered ranged from 44% as urea to 64% as UF‐15. In the forced‐draft NH3 volatilization study, total NH3 losses were reduced from 55% of the applied N as urea to 34% as MDU, and as the proportion of PFA addition to urea increased, NH3 losses decreased: % of applied N volatilized = 54.74 − 1.25%PFA. Ammoniacal N concentrations in the floodwater peaked on the 1st d after fertilizer application with urea and UF but peaked on the 7th d with MDU.

15N tracer investigations of the physiological availability of urea nitrogen in mother's milk.

The physiological availability of urea in mother's milk was investigated in tracer studies using [15N]2 urea and involving 22 infants. The incorporation of 15N into the body protein was established in 16 subjects by emission spectrophotometrical determination of the 15N excess in the serum protein. Between 2% and 3.6% of the serum protein is synthesized from the urea nitrogen in mother's milk. In further studies on the 15N balance in 6 infants, renal excretion of 15N after oral multiple and single impulse labelling with [15N]2 urea constituted 60% of the dose administered. Three-tenths-2.5% was excreted in the feces. The retention of 15N in the protein pool varied between 16.7 and 61.4%.

Effects of Phenylphosphorodiamidate and Dicyandiamide on Nitrogen Loss from Flooded Rice

AbstractThe effects of a urease inhibitor, phenylphosphorodiamidate (PPD), and a nitrification inhibitor, dicyandiamide (DCD), on the losses, tranformations, and recovery of nitrogen (N) were studied when urea was applied to a flooded rice field near Griffith, New South Wales (NSW). When PPD was applied with urea to the floodwater, urea hydrolysis was not prevented but merely delayed by ∼4 d. Consequently, the accumulation of ammoniacal N in the floodwater was also delayed. The maximum ammoniacal N concentration was reached after 3 d in the urea control, and after 9 d in the urea + PPD treatment. The relative losses of ammonia (NH3) from the treatments thus depended on the temperatures and pH of the floodwater and the windspeeds prevailing during the respective periods when the concentration of ammoniacal N was high. Low windspeeds at 8 to 10‐d after application caused NH3 loss on the PPD‐treated plots to be less than on urea‐only plots, but this was fortuitous and an opposite effect might have occurred. The 15N balance on microplots which received labelled urea showed that PPD addition increased recovery of urea N in the plant‐soil system from 60 to 82%. Plant uptake of labelled N was increased by 56%. After subtracting NH3 volatilization and any other potential losses, the resultant N balance suggested that PPD addition had allowed more urea N to be retained in the soil surface layer (0–10 mm) in such a way that nitrification‐denitrification loss was substantially reduced. The nitrification inhibitor (DCD) had no significant effect on nitrate concentrations in the floodwater, NH3 loss, or recovery of fertilizer N in plants and soil.

Irrigation of Forages with Rendering Plant Wastewater: Forage Yield and Nitrogen Dynamics

AbstractWastewater from an animal by‐product rendering plant containing N, P, and biochemical oxygen demand (BOD) at greater than 500, 60, and 500 mg L−1, respectively, was applied to irrigated forages to study the suitability of forage species and the fate of applied nutrients. Applications of 10 and 20 cm yr−1 supplied the nutrients at rates in excess of crop requirements. The treatments were compared with irrigation water and with water supplemented with either fertilizer N and P or C as sugar at rates similar to those in the wastewater. Reed canarygrass (Phalaris arundinacea L.) yields were doubled by the application of 10 cm yr−1 of wastewater as compared with irrigation water treatments, but alfalfa (Medicago sativa L.) yields were not significantly affected. Doubling the wastewater application rate or adding comparable rates of N and P fertilizer did not further increase yields. The wastewater‐irrigated alfalfa contained NO3−‐N levels of 1500 to 1600 mg kg−1 plant material, while reed canarygrass contained about 3000 to 3400. Both these levels would be considered potentially unsafe for livestock feed. There was an accumulation of soil NO3−‐N levels of up to 30 to 40 mg kg−1 soil throughout the surface 120 cm of soil after 5 yr of irrigation with 10 cm yr−1 of wastewater and two to three times this level with 20 cm yr−1 of wastewater. Higher levels of NO3−‐N were observed in the soil when N was applied as fertilizer. Soil NH4+‐N levels were not greatly affected. A nitrogen balance over 6 yr at the high application rate suggested plant uptake, soil NO3−‐N, and losses accounted for 30, 25, and 45% of wastewater N and 29, 39, and 32% of fertilizer N. A 1‐yr 15N balance after 3 yr of irrigation indicated uptake, soil NO3−‐N, and unaccounted‐for N was about 10, 19, and 71% for wastewater and 15, 33, and 52% for fertilizer N. The greater losses of wastewater N compared with fertilizer N were attributed to enhanced denitrification due to oxidizable C in the wastewater. Attempts to simulate this effect with C as sugar were not effective.

Fate of urea nitrogen applied at planting to grain sorghum grown under sprinkler and furrow irrigation on a cracking clay soil

Uptake of nitrogen (N) fertilizer and yields of grain by sorghum on Cununurra clay in north-western Australia have been found previously to be higher under sprinkler than under furrow irrigation. The cause of this was investigated using a 15N balance technique on field microplots. Additional data on sequential changes in the distribution of mineral-N in the soil, and on volatilization of ammonia, were collected from outside the 15N microplots. The improved effectiveness of N fertilizer under sprinkler irrigation was associated with less upward movement of 15N into the top of the ridge and thus out of the rooting zone of the crop. Furrow irrigation caused 22% of the 15N applied to move into the top of the ridge, sprinkler irrigation caused only 2% of the 15N to do this. The urea appeared to move upwards during the first irrigation, and this N became unavailable to the sorghum because of soil dryness, high temperatures, and osmotic effects in the surface soil. Loss of 15N from the soil-plant system was approximately 27% under both systems of irrigation. This loss was attributed to denitrification, because there was no evidence for large losses of N by leaching or volatization of ammonia.

Field estimation of ammonia volatilisation from 15N‐labelled urea fertiliser

AbstractGranules of 15N‐labelled urea (150 kg N ha−1), with or without the urease inhibitor hydroquinone, were broadcast on to small plots of winter oilseed rape in March. Ammonia volatilisation losses were estimated by a 15N balance procedure in which the amount of 15N in the plants, plus that in the soil to 70 cm depth, was determined 18 days after urea application. All the urea‐N was recovered in soil and plants from plots given either urea alone or urea plus hydroquinone; hence there was no volatilisation of ammonia. Although the soil pH was high enough (7.7 to 8.0) for ammonia loss, this did not occur because the soil was too cold, too wet and had a high cation exchange capacity.

Nitrogen‐15 Balance and Residual Effects of Urea‐N in Wetland Rice Fields as Affected by Deep Placement Techniques

AbstractThe 15N balance at harvest, the residual effects of applied N fertilizer, and the distribution of N by depth in a wetland rice (Oryza sativa L.) soil (Alfisol) were determined in field experiments using 15N‐labeled urea. Nitrogen‐15 balance data show that with point, deep placement of urea supergranules (USG), only 4 to 5% of the applied N was unaccounted for after harvest of both the dry‐season and wet‐season crops. In contrast, when prilled urea was basally broadcast and incorporated and topdressed at panicle initiation (PI), 11 to 35% of the applied N was not recovered at harvest, indicating substantial loss of fertilizer N, especially when poor incorporation resulted in high floodwater mineral‐N levels. Uniform deep placement also resulted in high recovery of 15N (92–107%), confirming that the high total 15N recovery obtained with point deep‐placement of USG was largely a function of depth of placement. Band application of urea gave complete 15N recovery (102%) in the dry season and low recovery (61%) in the wet. Nitrogen‐15 balance data showed that 22 to 56% of the applied urea‐N still remained in the soil after the final harvest. The uptake by the wet season crop of the residual labeled soil N from the dry season experiment was about 5% of the initial applied N (87 kg N/ha) for all treatments. Placement method appeared to influence the actual recovery of residual soil 15N; the percentage recovery from the USG treatment was highest and that from the split urea treatment lowest. In neither the dry season nor the wet season was 15N enrichment significant in soil below 30 cm. Generally, the distribution of the residual 15N in soil reflected the placement pattern of urea.

Nitrogen Loss from Freshwater and Saline Estuarine Sediments

AbstractThe magnitude of ammonium‐N (NH4+‐N) loss from nitrification‐denitrification reactions in bottom sediments collected from saline and freshwater Louisiana Gulf Coast lakes was determined. Studies were conducted in the laboratory and field. Maximum gaseous N accumulation, from fresh‐water and saline sediment amended with 4.5 µg nitrate‐N (NO4−‐N) g−1 (on dry‐wt basis), was 1.6 and 1.4 µg N g−1, respectively. The addition of 50 µg NH4+‐N g−1 stimulated the evolution of N2O from both sediments, and represents 0.02 and 0.2% of the NH4+‐N applied to the saline and fresh sediment, respectively. Nitrous oxide (N2O) emissions measured in the field were low. The annual N2O emission was 10 and 34 mg N m−2 from the saline and freshwater lakes. These values agree closely with the N2O emission rates calculated from laboratory data.Denitrification was also estimated from NH4+‐N amended sediment using the acetylene (C2H2) inhibition technique and 15N balance. Recovery of 15N decreased rapidly during the 0‐ to 8‐week period when high denitrification rates were measured. The denitrification rate estimated from 15N recovery during the 0‐ to 8‐week period was 3.7 mg N m−2 d−2 for each sediment. Approximately 50% of the added 15N was lost, an amount equivalent to 1.4 g N m−2 y−1. As the added 15NH4+‐N was incorporated into the organic N pool, little or no further 15N was lost.

Influence of Potassium Nutrition of Ryegrass and Soil Moisture on Denitrification

AbstractThe influence of potassium nutrition on denitrification in the soil was investigated in a pot experiment with ryegrass fertilized with 15N‐Ca(NO3)2. After harvesting a 15N balance was drawn up. At 70% water holding capacity of the soil 15N was recovered completely in all 3 potassium treatments. At 90%, complete recovery was observed at the two higher K levels. At the lowest postassium level, however, only 89% of the added 15N was recovered. The non‐recovered portion was obviously lost by denitrification. The denitrification associated with low potassium nutrition is probably due to an increased microbial activity in the rhizosphere.

Nitrogen metabolism of broilers fed 15-N labeled wheat.5. Skin, feathers and 15-N balance

In the present study 17 four-week-old broilers received a ration supplemented with 15N labelled wheat for a period of 2 days. The 15N excess was 295mg. 3 birds each were killed 3, 6, 12, 60 and 108 hours after administration of the last 15N dose. The present communication provides data on the N and 15N content of the bone skin, feathers and data on the 15N balance. On an average, 11% of the amount of 15N administered were found in medullar bones. A fairly uniform pattern of 15N labelling was observed at the different test points of the skin while the time pattern of 15N frequencies in the feathers was non-directional. 15N' balance showed that at all the 6 test point the range of error for the recovery rates was less than 3%. The present study substantiated the suitability of the stable N isotope for use in N metabolism trials.

Isotopic studies on the uptake of nitrogen by pasture plants. V. 15N balance experiments in field microplots

Recovery of 15N from labelled fertilizers was measured in open microplots on pastures at three sites in southern Queensland. Very little 15N was recovered from plants growing further than 15-30 cm from the area of application. Most of the 'N found in soil and roots was in the top 15 cm of the profile. The following total recoveries of 15N (with their standard errors) were recorded: 83.0�2.7% from ammonium sulphate applied to Rhodes grass; 76.6 �3.7 % from potassium nitrate on a Townsville stylo-spear grass pasture; and 97.9�6.7% from urea applied to a Nandi setaria pasture. The weather during the three experiments was relatively dry, and it is unlikely that any ISN was leached below the depth of sampling. The advantages and disadvantages of open and enclosed microplots are discussed in some detail. It is suggested that while open microplots are satisfactory for some purposes, the use of plots enclosed by steel cylinders pressed into the soil is probably the most accurate technique available for 15N balance studies in the field.