Ammonia Volatilization Losses Research Articles

English

The faster urea hydrolyses process leads to high amount of ammonia gas emission from urea fertilized fields. Coating of urea with various materials is the most successful strategy to control N losses from urea fertilized fields. A laboratory study was conducted to evaluate the effects of uncoated urea, as compare to urea coated with hydroquinone and Cu on NH3 volatilization loss and rate of urea hydrolysis in soil. The coated urea treatments were prepared by using Cu and hydroquinone solutions with a fluidized bed coating machine. Two experiments were carried out to evaluate the coated urea treatments labelled as UCu (Cu coated urea) and UHY (Hydroquinon urea). Both experiments were carried out on a sandy soil named as Serdang series. The soil was characterized for its properties by standard methods. In the first experiment the coated urea was evaluated for ammonia volatilization loss by using closed chamber force draft technique. Simultaneously, an incubation experiment was conducted to evaluate the effect of hydroquinone and Cu coated urea treatments for their hydrolyses rate or mineralization process. It was estimated by the results that ammonia volatilization from Hydroquinon coated urea treated soil reduced 25% however, Cu coated urea showed 30% reduction in ammonia volatilization loss as compare to uncoated urea. In incubation experiment recovery of urea from soil was 50% more in coated urea as compare to uncoated urea. It is concluded that coating of urea with urease inhibitors can reduce successfully the ammonia volatilization loss and increased the recovery of urea either coated by Cu or hydroquinone. Key words: Urease inhibitor, urea, hydroquinone, Cu (Copper).

Ammonia volatilization losses were small after mowing field peas in dry conditions

Engel, R., Jones, C. and Wallander, R. 2013. Ammonia volatilization losses were small after mowing field peas in dry conditions. Can. J. Soil Sci. 93: 239–242. Ammonia losses following termination of peas (Pisum sativum L.) by mowing were measured using a micrometeorological mass-balance approach. Field trials were conducted during two seasons in a semiarid climate. Plant N in the above ground biomass was 105 and 79 kg N ha−1 in 2011 and 2012, respectively. Vertical NH3 flux estimates were nominal (0.3 to 1.7 g N ha−1 h−1) in the 2 wk following mowing. Cumulative NH3 loss represented 0.3 to 0.5% of the N in plant biomass, indicating that N fertility was not diminished by NH3 volatilization in this dry climate.

Ammonia volatilization losses were small after mowing field peas in dry conditions

Engel, R., Jones, C. and Wallander, R. 2013. Ammonia volatilization losses were small after mowing field peas in dry conditions. Can. J. Soil Sci. 93: 239-242. Ammonia losses following termination of peas (Pisum sativum L.) by mowing were measured using a micrometeorological mass-balance approach. Field trials were conducted during two seasons in a semiarid climate. Plant N in the above ground biomass was 105 and 79 kg N ha-1 in 2011 and 2012, respectively. Vertical NH3 flux estimates were nominal (0.3 to 1.7 g N ha-1 h-1) in the 2 wk following mowing. Cumulative NH3 loss represented 0.3 to 0.5% of the N in plant biomass, indicating that N fertility was not diminished by NH3 volatilization in this dry climate.

Ammonia volatilization and nitrous oxide emissions during soil preparation and N fertilization of elephant grass (Pennisetum purpureum Schum.)

Promising renewable fuels such as elephant grass in Brazil are under critical examination with reference to greenhouse gases (GHGs) produced during the production phase, especially with regard to the impact of nitrous oxide (N2O) emissions. The objective of this field study was to examine the impact of N fertilization on biomass yield, plant N accumulation, emissions of N2O and ammonia (NH3) volatilization grown on an Acrisol typical of large regions of the Atlantic coast of Brazil over a period of 618 days, covering three growth cycles of elephant grass with three harvests. The tillage required for planting the crop produced emissions of N2O totalling 726 g N2O–N ha−1, representing approximately 0.6% of the mineralized N as estimated from the soil CO2 emission. Reduction in tillage operations prior to planting would reduce N2O emissions and preserve soil C stocks. There was only a small response of biomass production to additions of urea fertilizer which may be related to the high loss of fertilizer N. Fertilizer induced N2O emissions were 173, 410 and 705 g N2O–N ha−1 for each growth cycle, respectively, equivalent to a mean emission factor (EF) of 0.51% with a confidence interval of 0.35–0.73%, almost half of the IPCC default EF of 1.0%. Ammonia volatilization losses were high, amounting to a mean of 49% of applied urea N, which is fivefold the IPCC default value (10%) and may indicate that indirect N2O emissions are currently underestimated.

Simulations of nitrogen dynamism in maize and rice by using CSM-CERES-maize and rice models under Chitwan, Nepal

Crop modeling is being popular in the field of agriculture as a precision tool for resources allocations and their effective utilizations. Two separate field and simulation studies were accomplished in maize and rice that were laid out in the two factor factorial randomized complete block design at Agronomy Farm of Institute of Agriculture and Animal Sciences, Rampur, Chitwan Nepal during spring and rainy season of 2007 and 2008, respectively. CERESmaize and rice models were calibrated using the best performing treatments (7.41 x 104 plants /ha for all 3 varieties of maize i.e. Rampur Composite, Upahar and Arun 4 and 160 kg N /ha for Prithivi and Sunaulo Sugandha, and 120 kg N /ha for Masuli varieties of rice). Models were validated using the remaining treatments (6.36, 5.56 and 4.76 x 104 plants /ha for all varieties in maize and 40, 80 and 120 kg N /ha for Prithivi and Sunaulo Sugandha and 40, 80 and 160 kg N /ha for Mansuli in rice) to predict growth and productivity of different varieties of maize and rice. Model calibration was done with the determination of genetic coefficients and validation was accomplished with the comparison of observed and simulated values on anthesis days, maturity days, leaf area indices, above ground biomass at maturity, unit weight, and grain yields for both maize and rice. The simulation results on nitrogen dynamics revealed that the nitrification and leaching losses were higher under the conditions of non-flooded maize whereas ammonia volatilization and denitrification losses were higher in the conditions of alternately wetting and drying flooded rice field. The degree and magnitude of N-loss is higher when the N-level is advancing under both field conditions. However, volatilization was almost nil in the non-flooded maize. Results indicated that CERESmaize and rRice models could be applied in simulating the agronomic management options including the efficiency of N-application under the conditions of availability of complete datasets required to run the Cropping System Models (CSM)-CERES-maize and rice models embedded under Decision Support System for Agro Technology Transfer (DSSAT) ver 4.2 in the coming days. DOI: http://dx.doi.org/10.3126/ajn.v1i0.7548 Agronomy Journal of Nepal (Agron JN) Vol. 1: 2010 pp.94-102

Effect of Superphosphate as Additive on Nitrogen and Carbon Losses during Pig Manure Composting

A pilot scale experiment of composting in rotting boxes used pig manure with cornstalks was carried out to study the effects of superphosphate on nitrogen and carbon losses including gas emissions. Besides control, there were five amended treatments with superphosphate addition (counted by P content) at 0.05, 0.10, 0.15, 0.20 and 0.25 molar ratio of initial nitrogen. The results indicated that superphosphate addition decreased ammonia volatilization, total nitrogen and carbon losses in composting. Total nitrogen losses of superphosphate-amended treatments were reduced by 9.3%, 14.6%, 30.1%, 45.8% and 71.5%, respectively. About 0.8% to 1.2% of initial nitrogen lost in the form of N2O emission, and the CH4 emission accounted for less than 0.3% of initial carbon. More than 0.15 molar ratio of superphosphate in compost materials caused considerable adverse effects on degradation of organic matter.

Polyolefin‐Coated Urea Decreases Ammonia Volatilization in a Double Rice System of Southern China

Field evaluations of slow‐release N fertilizers are needed to improve N use efficiency while reducing NH3 volatilization. Ammonia volatilization losses, floodwater NH4+, and aboveground rice (Oryza sativa L.) tissue N accumulation were compared between non‐coated urea (NCU) and polyolefin‐coated urea (POCU) applications in a double‐rice production system of subtropical China. A factorial treatment design included two urea sources such as POCU and NCU applied at 75 and 150 kg N ha−1, and a no‐N control. For early and late rice seasons, floodwater NH4+ and pH increased significantly within 7 to 10 d after NCU applications and then decreased rapidly. Nitrogen losses through NH3 volatilization accounted for 16 to 30% and 4 to 8% of the total N applied for NCU and POCU, respectively. Applications of POCU significantly increased N accumulation in aboveground rice biomass due to a slower N release and better synchrony between in‐season rice N demand and N supply from this fertilizer. Applications of POCU at a rate of 75 kg N ha−1 provided the optimal amounts of N for early and late rice crops and reduced NH3 volatilization losses. The use of slow release urea fertilizers should increase N use efficiency and maintain the high grain yield in the double rice production systems of subtropical China.

Ammonia volatilization in gemmiparous and early seedling stages from direct seeding rice fields with different nitrogen management strategies: A pots experiment

Ammonia volatilization (AV) from direct seeding rice (DSR) fields in gemmiparous and early seedling stages was measured to reveal the effect of nitrogen (N) fertilizer management by pots experiment, and compared with those from traditional transplant rice paddies. There were three N fertilizer types, urea (U), ammonium bicarbonate (AB), and control released urea (CRU), which were applied through surface broadcasting (S) or 5cm depth placement (D). The cumulative AV losses within four weeks after sowing from DSR pots were 35.8, 23.6, 17.6, 27.0, 18.4 and 16.3kgNha−1 for the treatments of AB+S, U+S, CRU+S, AB+D, U+D, and CRU+D, respectively, accounting for 59.7, 39.3, 29.3, 45.1, 30.6 and 27.6% of N application for each treatment. The lowest AV losses incurred with the combined CRU+D treatment. The absence of crop uptake and canopy shelter, the very low ponding water depth during gemmiparous and seedling stages in DSR fields favored the AV process, and resulted in much higher AV losses than in traditional transplanting rice fields. The N fertilizer type was the predominant factor that caused AV loss in DSR fields. AB resulted in much higher AV losses from the DSR fields than U and CRU. The 5cm deep placement of N reduced AV rates and lagged the AV process. The suitable N fertilizer type and application method for basal fertilizer in DSR fields were CRU and deep placement, respectively. Dividing the basal fertilizer into two splits, and fertilizing with proper N fertilizer types and methods should be the efficient measures to mitigate the AV losses from DSR paddies.

Nitrogen Transformation, Ammonia Volatilization Loss, and Nitrate Leaching in Organically Enhanced Nitrogen Fertilizers Relative to Urea

Nitrogen Transformation, Ammonia Volatilization Loss, and Nitrate Leaching in Organically Enhanced Nitrogen Fertilizers Relative to Urea

Gaseous losses of nitrogen by ammonia volatilization and nitrous oxide emissions from rice paddies with different irrigation management

To reveal the influence of non-flooding controlled irrigation (NFI) on gaseous nitrogen (N) losses in forms of ammonia volatilization (AV) and nitrous oxide (N2O) emissions from high N inputs rice paddies, lysimeter experiments were conducted with flooding irrigation (FI) as check. Compared with FI paddies, AV losses in NFI paddies decreased by 18.5–20.5 % and N2O emissions increased by 1.43–1.9 kg N ha−1. Weekly AV losses immediately after fertilization accounted for over 83 % of seasonal losses in both treatments. High N2O emissions from NFI paddies always occurred in drying process after N application, with peaks observed when water-filled pore space (WFPS) fell in 75–85 %. Water management immediately after N fertilization is crucial for mitigating gaseous N losses from rice paddies. Bringing N into shallow rhizosphere by irrigation and covering it with deep water will be helpful in preventing AV. Maintaining a flooding period and keeping WFPS higher than 85 % in the first drying process after fertilization might be effective to reduce N2O emissions peaks for NFI paddies.

Ammonia volatilization losses from surface-applied urea with urease and nitrification inhibitors

Urease inhibitor (UI) and nitrification inhibitor (NI) have the potential to improve N-use efficiency of applied urea and minimize N losses via gaseous emissions of ammonia (NH3) to the atmosphere and nitrate (NO3−) leaching into surface and ground water bodies. There is a growing interest in the formulations of coating chemical fertilizers with both UI and NI. However, limited information is available on the combined use of UI and NI applied with urea fertilizer. Therefore the aim of this study was to investigate the effects of treating urea with both UI and NI to minimize NH3 volatilization. Two experiments were set up in volatilization chambers under controlled conditions to examine this process. In the first experiment, UR was treated with the urease inhibitor NBPT [N-(n-butyl) thiophosphoric acid triamide] at a rate of 1060 mg kg−1 urea and/or with the nitrification inhibitor DCD (dicyandiamide) at rates equivalent to 5 or 10% of the urea N. A randomized experimental design with five treatments and five replicates was used: 1) UR, 2) UR + NBPT, 3) UR + DCD 10%, 4) UR + NBPT + DCD 5%, and 5) UR + NBPT + DCD 10%. The fertilizer treatments were applied to the surface of an acidic Red Latosol soil moistened to 60% of the maximum water retention and placed inside volatilization chambers. Controls chambers were added to allow for NH3 volatilized from unfertilized soil or contained in the air that swept over the soil surface. The second experiment had an additional treatment with surface-applied DCD. The chambers were glass vessels (1.5 L) fit with air inlet and outlet tubings to allow air to pass over the soil. Ammonia volatilized was swept and carried to a flask containing a boric acid solution to trap the gas and then measured daily by titration with a standardized H2SO4 solution. Continuous measurements were recorded for 19 and 23 days for the first and second experiment, respectively. The soil samples were then analyzed for UR–, NH4+–, and NO3−–N. Losses of NH3 by volatilization with unamended UR ranged from 28 to 37% of the applied N, with peak of losses observed the third day after fertilization. NBPT delayed the peak of NH3 losses due to urease inhibition and reduced NH3 volatilization between 54 and 78% when compared with untreated UR. Up to 10 days after the fertilizer application, NH3 losses had not been affected by DCD in the UR or the UR + NBPT treatments; thereafter, NH3 volatilization tended to decrease, but not when DCD was present. As a consequence, the addition of DCD caused a 5–16% increase in NH3 volatilization losses of the fertilizer N applied as UR from both the UR and the UR + NBPT treatments. Because the effectiveness of NBPT to inhibit soil urease activity was strong only in the first week, it could be concluded that DCD did not affect the action of NBPT but rather, enhanced volatilization losses by maintaining higher soil NH4+ concentration and pH for a longer time. Depending on the combination of factors influencing NH3 volatilization, DCD could even offset the beneficial effect of NBPT in reducing NH3 volatilization losses.

Nitrogen Sources and Timing Effects on Nitrogen Loss and Uptake in Delayed Flood Rice

Field experiments were conducted in 2009 and 2010 in Louisiana and Mississippi to evaluate ammonia volatilization loss and subsequent effects on apparent nitrogen recovery efficiency (ANRE) and grain yield for rice (Oryza sativa L.). A semi‐open static chamber approach was used to measure ammonia volatilization loss from multiple N sources applied 10 days before flood (dbf) at the rate of 168 kg N ha−1. Cumulative ammonia volatilization losses for urea for Louisiana environments were 19 and 33% compared to 7% for both Mississippi environments. Urea + [N‐(n‐butyl) thiophosphoric triamide] (NBPT), urea + NBPT + dicyandiamide (DCD), and ammonium sulfate (AS) all minimized volatilization losses over all environments (range of 1.9–4.9%). Additionally, ammonia volatilization data fitted to the Gompertz model demonstrated that urea + NBPT and urea + NBPT + DCD had longer lag phases (7.2–7.7 d) relative to urea, AS, and urea + ammonium sulfate (UAS) blend (3.6 d). The same N sources and rate of N was applied 10, 7, 4, and 1 dbf to determine the effects on ANRE and yield. Apparent N recovery efficiency ranged from 43 to 71%. Grain yield was influenced by application time for two environments. Nitrogen application 10 dbf resulted in the least grain yield and yields tended to increase with fewer days between application and permanent flood. In Louisiana, urea + NBPT and urea + NBPT + DCD resulted in yields greater than urea alone. Where volatilization potential is substantial, NBPT should be included with the urea application to protect yield potential.

Ammonia volatilization losses from a rice paddy with different irrigation and nitrogen managements

Abstract Ammonia volatilization (AV) is one of the main pathways of nitrogen (N) loss from a rice paddy, which results in low N use efficiency and many other environmental problems. To reveal AV losses from rice paddies with different combined irrigation and N managements, field experiments were conducted using site-specific nutrient management (SSNM), controlled released nitrogen management (CRN), and non-flooding controlled irrigation (NFI). The interactive effect of N management and irrigation management on AV losses is significant. N management is the dominant management factor of AV losses from a rice paddy. Weekly AV losses followed by fertilization comprise the majority of seasonal AV losses. Ammonium contents in surface water or top soil solutions determine the AV loss rate for both flooding irrigation (FI) and NFI paddies. Moreover, AV losses are less sensitive to surface ammonium nitrogen contents for the NFI paddy than that for the FI paddy. Shallower water condition in the NFI paddy immediately after fertilization may result in higher AV losses than that in the FI paddy in a short term during the first wet–dry cycle after fertilization. However, the following wet–dry cycles result in lower AV losses in most of the rice growth stages. Seasonal AV losses from the NFI paddy using farmers’ fertilization practice (FFP), SSNM, and CRN treatments were 125.27, 37.63, and 23.73 kg N ha−1, which account for 31.1%, 23.2%, and 13.2% of the seasonal N inputs, respectively. These results were reduced by 14.0%, −17.1%, and 28.7% compared with those from the FI paddy with the same N management. A combination of NFI and CRN is the optimal treatment, with the lowest AV losses and high potential in reducing nutrient leaching risks. Increasing the water depth and the duration of flooding for the first wet–dry cycle after fertilization is a promising measure to reduce AV losses and improve N use efficiency in an NFI paddy.

Nitrogen Isotope Fractionation and Origin of Ammonia Nitrogen Volatilized from Cattle Manure in Simulated Storage

A series of laboratory experiments were conducted to establish the relationship between nitrogen (N) isotope composition of cattle manure and ammonia emissions, potential contribution of nitrogenous gases other than ammonia to manure N volatilization losses, and to determine the relative contribution of urinary- vs. fecal-N to ammonia emissions during the initial stage of manure storage. Data confirmed that ammonia volatilization losses from manure are most intensive during the first 2 to 3 days of storage and this coincides with a very rapid loss (hydrolysis) of urinary urea. Long-term (30 days) monitoring of δ15N of manure and emitted ammonia indicated that the dynamics of N isotope fractionation may be complicating the usefulness of the isotope approach as a tool for estimating ammonia emissions from manure in field conditions. The relationship between δ15N of manure and ammonia emission appears to be linear during the initial stages of manure storage (when most of the ammonia losses occur) and should be further investigated. These experiments demonstrated that the main source of ammonia-N volatilized from cattle manure during the initial 10 days of storage is urinary-N, representing on average 90% of the emitted ammonia-N. The contribution of fecal-N was relatively low, but gradually increased to about 10% by day 10. There appears to be substantial emissions of nitrogenous gases other than ammonia, most likely dinitrogen gas, which may account for up to 25% of N losses during the first 20 days of manure storage. This finding, which has to be confirmed in laboratory and field conditions, may be indicative of overestimation of ammonia emissions from cattle operations by the current emissions factors.

Ammonia volatilization and yield response of energy crops after fertilization with biogas residues in a coastal marsh of Northern Germany

Anaerobic co-fermentation of animal slurries and crop silages leads to new types of biogas residues with an uncertain fertilizer value. Ammonia volatilization losses and crop productivity after supplying co-fermented biogas residues were investigated at a marshland site in Northern Germany. Due to the ecological risks of monocultures, maize (Zea mays) in monoculture as the dominant biogas crop in the marsh was tested against a crop rotation (maize, wheat (Triticum aestivum), Italian ryegrass (Lolium multiflorum)) and perennial ryegrass (Lolium perenne). Biogas residues, applied by trail hoses, and CAN (mineral fertilizer) were used as nitrogen fertilizers. Ammonia losses at all application dates were investigated by an approach including passive flux samplers and a calibrated dynamic chamber method. Simultaneously a micrometeorological technique was used as a reference. A comparison of methods showed a close correlation (r2=0.92) between micromet and passive flux sampler techniques. Ammonia volatilization losses (on average 15% NH4+-N applied) occurred mainly within the first 10h. Concomitant with high ammonia losses, a significant yield depression of 5tDMha−1 for ryegrass fertilized by biogas residues compared to CAN was observed. Little or no affect of biogas was observed for maize and wheat. The crop rotation had yields (34tDMha−12year−1) that were comparable with the maize monoculture (31tDMha−12year−1).

Role of inhibitors and biodegradable material in mitigation of nitrogen losses from fertilized lands

Loss of N, occurring mainly through NH 3 volatilization, biological denitrification, and NO 3 - leaching, has both economic and environmental implications. Therefore, the economic benefits of reduced environmental pollution and future damage to our environment as a result of the use of urease inhibitors are of higher significance to the production of gains over the long-term. The literature review discussed the role, effectiveness and mechanism of urease inhibitors as well as coating of urea to reduce ammonia volatilization loss from urea fertilizer. Coating with urease inhibitors can improve the bioavailability of N, resulting in increased dry matter yield and N uptake. Such increases result from delayed urea hydrolysis by urease inhibitors and coating materials. The value of inhibitors in mitigating N loss would depend on their rate of biodegradation and persistence in soils. Previous studies has proven that micronutrients could be competent urease inhibitors, but the information about their effects on soil, nutrient uptake of plants and dry matter yield is poorly documented. Some nutrients such as Cu and Zn as urease inhibitors and natural biodegradable material such as agar, gelatin and palm stearin were found effective in reduction of nitrogen losses from nitrogen fertilizer especially from urea fertilizer. The article deals with the importance of use of above mentioned materials and micronutrient. Key words : Nitrogen, urea, fertilizer, inhibitors, biodegradation, land, nitrogen loss.

Manure Application Technology in Reduced Tillage and Forage Systems: A Review

Managing manure in reduced tillage and forage systems presents challenges, as incorporation by tillage is not compatible. Surface-applied manure that is not quickly incorporated into soil provides inefficient delivery of manure nutrients to crops due to environmental losses through ammonia (NH3) volatilization and nutrient losses in runoff, and serves as a major source of nuisance odors. An array of technologies now exist to facilitate the incorporation of liquid manures into soil with restricted or minor soil disturbance, some of which are new: shallow disk injection; chisel injection; aeration infiltration; pressure injection. Surface banding of manure inforages decreases NH3 emissions relative to surface broadcasting, as the canopy can decrease wind speed over the manure, but greater reductions can be achieved with manure injection. Soilaeration is intended to hasten manure infiltration, but its benefits are not consistent and may be related to factors such as soildrainage characteristics. Work remains to be done on refining its method of use and timing relative to manure application, which may improve its effectiveness. Placing manure under the soil surface efficiency by injection offers much promise to improve N use efficiency through less NH3 volatilization, reduced odors and decreased nutrient losses in runoff, relative to surface application. We identified significant gaps in our knowledge as manyof these technologies are relatively new, and this should help target future research efforts including environmental, agronomic, and economic assessments.

Limited ammonia volatilization loss from upland fields of Andosols following fertilizer applications

The present study first aimed to investigate the ammonia (NH 3) volatilization loss from broadcast ammonium sulfate at an upland field of volcanic ash soil (Andosol) in Hokkaido, northern Japan. Ammonium sulfate was applied for the regrowing stage of wheat at a rate of 300 kg ha −1 (= 63.6 kg N ha −1). A micrometeorological technique (i.e., the gradient method) was used to determine the atmosphere-upland field exchange of NH 3. A dynamic chamber method was also tested to separate the contributions of the soil surface and wheat to the exchange fluxes. Although the NH 3 volatilization began one day after the fertilizer application, the cumulative loss accounted for only 0.2% of the applied nitrogen. Hence, the present study also examined the features of Andosols in terms of the inhibition of NH 3 volatilization. Existing studies support the suggestion that upland fields of Andosols inhibit the NH 3 volatilization loss compared to non-Andosols. The following were the key features of Andosols that might inhibit NH 3 volatilization: the relatively low soil pH; the relatively high effective cation exchange capacity even at a low soil pH; and the relatively high nitrification potential, signifying a high consumption rate of the applied ammonium.

Ammonia volatilization and nitrogen balance after topdressing fertilization in paddy fields of Taihu Lake region

采用密闭室通气法和¹⁵N 微区试验, 对太湖地区水稻不同生育期追施氮肥的氨挥发损失、水稻对氮肥的吸收利用和土壤氮素残留情况进行了研究。结果表明, 氨挥发损失主要发生在施肥后1 周内, 峰值出现在施肥后1~2 d, 氨挥发速率变化与田面水NH₄⁺-N 浓度变化规律一致, 分蘖肥和穗肥氨挥发损失率分别为16.7%和6.3%; 水稻分蘖肥的作物氮素利用率低于穗肥, 分别为36.7%和49.6%, 主要原因是穗肥的氨挥发损失较少,并且更易于向籽粒转移; 2 次追施氮肥的表观损失率分别为52.8%和40.7%; 在土壤中残留肥料氮为10.6%, 大都集中在0~20 cm 土壤中, 耕层以下较少。本结果表明, 在水稻孕穗时期施氮肥有利于提高氮肥利用效率、减少氮肥损失, 主要体现在穗肥拥有较低的氨挥发损失率和较高的籽粒利用率。

Evaluation of coated urea for ammonia volatilization loss, nitrogen mineralization and microsite pH in selected soil series

The increase in microsite soil pH due to surface application of urea to the soil is an important reason of ammonia volatilization loss and fast hydrolysis process. The use of Cu and Zn with biodegradable materials coatings were assumed to reduce ammonia volatilization losses by reducing soil pH and slowing down hydrolysis process. The present study was conducted to evaluate the effects of coated urea with the combination coatings of Cu, Zn, palm stearin, agar and gelatine on microsite pH. For this purpose, six urea treatments named; uncoated urea or control, Cu and palm stearin coated urea, Cu and agar coated urea, Cu and gelatine coated urea, Cu coated urea, Cu and Zn coated urea were prepared and evaluated for their effects on microsite pH, ammonia volatilization loss and mineralization of N in three tropical soil. For the each soil; soil properties, soil microsite pH, ammonia volatilization loss and N mineralization were determined with slandered methods. The results reveal that the microsite pH in the three soils varied significantly due to the variability in texture. The pH of microsite treated with coated urea was lower than the uncoated urea treatments in each soil. The reduction in the microsite soil pH was associated with urea hydrolysis. The rate of mineralization (30%) and ammonia volatilization (50%) reduced in the soils where the pH was low or stable on the fertilizer microsite after adding the fertilizer treatments. The results of this study proved the positive effectiveness of coating material and potential to control fast hydrolysis process and ammonia volatilization losses. Key words: Ammonia volatilization, microsite pH, nitrogen, urease inhibitors.