Effects of initial soil calcium content on ammonia losses from surface-applied urea and calcium-urea

Ammonia loss from surface-applied urea occurs because urea hydrolysis increases the pH of the placement site microenvironment. Addition of Ca-salts with urea will control or reduce the microsite pH, thus reducing NH₃ losses. The degree of Ca-saturation of the cation exchange sites may influence the ratio of calcium:urea required to control ammonia loss. A laboratory study was conducted to determine if adsorbed Ca or CaCO₃ additions (acid soils only) had a measureable impact on Ca control of NH₃ loss from surface applied urea at various Ca:urea ratios.With urea alone applied to the soil surface varying the adsorbed Ca content of the treatment soil did not influence NH₃ loss. The addition of CaCl₂ with urea on the same pretreated soils generally resulted in NH₃ losses reflecting the initial pH of the soil. The Ca-saturated acid soils and those acid soils receiving CaCO₃ had higher NH₃ losses than untreated soils in the presence of urea with soluble CaCl₂. It was noted that increasing the calcium:urea ratios progressively depressed the NH₃ loss from all soils. Increasing the percent Na-saturation of the calcareous Harkey soil to 25 and 50% (ESP) reduced Ca control of NH₃ loss due to Ca being exchanged for Na on the cation exchange sites.Inclusion of CaCl₂ with the urea mixture on the surface of the pretreated acid soils resulted in stepwise differences in NH₃ loss concuring with the increases in pretreatment soil pH values (differing exchangeable Ca content). Other parameters that influence the amount of NH₃ loss, such as acidic buffer capacity and CEC, appeared more important than anticipated for control of NH₃ loss with the calcium:urea mixture. On Ca enriched soils the calcium:urea mixture was only slightly less effective in its ability to control NH₃ losses than on untreated soils.Contribution from the Texas Agric. Exp. Sta., Texas A&M University System, College Station, TX 77843, USA     

Ammonia losses from surface-applied urea as related to urea application rates,plant residue and calcium chloride addition

Volatile losses of NH₃ from surface-applied urea are known to decrease in the presence of soluble Ca-salts or with a decrease in easily decomposable organic matter content (EDOM), both of which influence urease activity. How these factors interact to affect NH₃ losses is not fully understood. Studies were conducted to determine the effect CaCl₂ in sand with varying rates of EDOM on NH₃ losses from surface applied urea. The same effects were examined on agricultural soils containing partially decomposed native organic matter (NOM). Determinations were made in the laboratory on field soils, sand free of organic matter and sand with known amounts of grass clippings (GC, EDOM). Low levels of GC in sand with low amounts of added urea resulted in little NH₃ loss. Ammonia loss increased as more N was applied at the low levels of GC. The loss was independent of urea application rates at high levels of GC. Ammonia losses were reduced more effectively at low EDOM and NOM in the presence of Ca. Incubation of sand with GC at low rates prior to urea addition increased NH₃ losses relative to high levels of non-incubated GC. For the above situation incubation for as high as 24 days resulted in equivalent NH₃ losses. The amount and state of decomposition of existing organic matter affected the degree of NH₃ loss from surface placed urea and its control by added Ca-salts. Microbial decomposition of EDOM, such as might occur in the spring prior to urea addition, led to greater NH₃ losses. Greater loss of NH₃ from urea might be an indication of a larger ureolytic microbial population leading to increased urease production.     

Effect of urea granule size on ammonia volatilization from surface-applied urea

Urea powder and granules of varying size (1 to 8 mm diameter) were surface applied to a ryegrass/white clover pasture. Evolution of NH₃ was measured using a continuous air flow enclosure method. At 30 kg N ha^–1, the percentage of urea-N lost as NH₃ from powder or granules of 1–2, 3–4, 5.6 and 8 mm diameter was 18, 17, 20, 22 and 32 respectively. As the particle size increased, the rate of urea hydrolysis decreased and delayed the time at which the maximum rate of volatilization occurred. Mineral-N and soil surface pH measurements confirmed that during the period of volatilization, urea moved less than 30 mm from the application point.For the powder and 3–4 mm granule treatments, when the application rate was increased from 30 to 300 kg N ha^–1, the percentage of urea-N volatilized increased, but at any particular rate there was no significant difference in percentage loss between the powder and 3–4 mm granules.     

Urea rate and placement for maize production on a calcareous Vertisol

A study of urea N rate and placement for irrigated maize (Zea mays L) grown in Somalia was conducted to investigate this most promising and rather easily adopted cultural practice, in order to sharply increase present low yields. This work was done at the Afgoi station of the Agricultural Research Institute on a calcareous Vertisol. Six different levels of N (0, 20, 40, 80, 160 and 320 kg N ha^?1) as urea were used as main-plot treatments with four different placements as subplot treatments. Three of the placements consisted of broadcast-incorporated, broadcast-not incorporated, and sidedress on or in dry soil while the fourth placement was broadcast on wet soil. The grain yield response to added N was very highly significant and the regression analysis predicted a maximum yield of 7.6 t ha^?1 from 210 kg N ha^?1. A consistent yield depression occurred at the 320 kg N ha^?1 rate in all placement treatments. Placement of urea on or in dry soil gave significantly higher yields than did placement on the wet soil. The data indicate that substantial N losses occurred on this soil when urea was broadcast on a wet surface. The economic analysis to determine the feasibility of applying N to maize grown under improved crop production practices showed that fertilization with N can be very profitable. At the existing price for urea and value of maize, the economic optimum occurred at 164 kg N ha^?1 which gave a 2.1 t ha^?1 grain yield increase. This increased yield from N fertilization produced a profit of 1010 Somali shillings (US $162) ha^?1.     

Effect of soil bulk density on hydrolysis of surface-applied urea in unsaturated soils

In situ hydrolysis of broadcast urea occurs in unsaturated soils with different bulk densities. The effect of increasing soil bulk densities on the hydrolysis of urea was studied in open and in covered unsaturated soil columns incubated at 30°C. An increase in bulk density from 0.8 to 1.4 Mg/m³ markedly increased the hydrolysis of surface-applied urea in soils containing water > 6% up to near field capacity. Increased diffusion of urea to sorbed soil urease with an increase in bulk density may have enhanced formation of urease-urea complexes and therefore increased the hydrolysis. As urea diffused farther in more dense soils, the retarding effects of high urea concentration gradients on the hydrolysis probably decreased. In light-textured soils, increases in the bulk density had no apparent effect on the hydrolysis of surface-applied urea when evaporation occurred.     

Effect of amounts and sequence of additions of urea and water on hydrolysis of surface-applied granular urea in unsaturated soils

The hydrolysis of surface-applied granular urea ( 15 mg of urea/particle) in 14 unsaturated soils as influenced by the amounts and the sequence of additions of urea and water and studied using open and covered soil column systems was in the following order: well-mixed surface-applied surface-applied surface-applied urea, granular urea, granular urea, granular urea, water added > water added > water added water added before, after, before, before, no drying no drying no drying drying The retarded hydrolysis' of surface-applied granular urea is attributed to retarded soil urease activity. Under the nondrying and drying conditions, the positive effect of increasing amounts of added water on the hydrolysis was less apparent when water was added 24–48 hours before than when it was added immediately after surface application of granular urea. When an increasing number of urea granules were evenly placed on a finite surface of unsaturated soil, the rate of urea application (quantity factor) increased but the percentage of urea hydrolyzed remained practically unchanged. These results suggest that it is necessary to consider effective urea concentration and effective urease activity for adequate understanding of in situ hydrolysis of broadcast fertilizer urea in unsaturated soil.     

Ammonia volatilization losses from different fertilizers and effect of several urease inhibitors,CaCl2 and phosphogypsum on losses from urea

The extent of ammonia volatilization losses from urea, ammonium sulphate (AS), and diammonium phosphate (DAP) were determined in soil incubation studies. The effects of some urease inhibitors (thiourea, hyroquinone, 2–4 dinitro phenol and boric acid) and CaCl₂ and phosphogypsum additions on ammonia loss from urea were also studied. Total ammonia volatilization losses were 32.6%, 3.1% and 2.3% of the N applied to the soil as urea, AS and DAP, respectively. Among the chemicals examined in the study, 500 mg H₃BO₃ in 1 kg of the soil decreased the ammonia loss from urea by 21% in comparison with the control. When 50 mg/kg soil of thiourea, 2–4 dinitro phenol or hydroquinone were applied, ammonia volatilization losses were found to be 10%, 3% and 0% less than urea applied alone, respectively. When 2500 mg CaCl₂ was applied to 1 kg of soil with urea, ammonia loss was decreased by 5%. The lowest hydrolysis rate (65%) occurred with the boric acid treatment. The differences between the hydrolysis rates of the other treatments were not statistically significant. Phosphogypsum was found the most effective agent in reducing ammonia losses from urea. When phosphogypsum was mixed at 2.3 times as much as the urea, ammonia loss was about 85% less than that of urea applied alone. Obviously, further work is needed to find out the potential of both boric acid and phosphogypsum as reducing agents of ammonia losses from urea.     

NH3气提尿素工厂设计应注意的几个问题

介绍了当今尿素生产工艺的流行趋势,对国内用户采用NH3气提的尿素生产工艺在设计及建设中应注意的问题进行了总结和剖析.     

Lowering ammonia volatilization losses from urea application by activation of nitrification process

The aim of this work was to lower ammonia volatilization losses by increasing the rate of nitrification. This was achieved by eliminating the gap in timing between urea hydrolysis and ammonium nitrification. Soils were pretreated with a small amount of ammonium salt which led to the activation of the nitrification process. When nitrification passed its lag period, urea was applied to the soils. Ammonium produced by urea hydrolysis was quickly oxidized into nitrate and did not accumulate in the soil. This resulted in decreased ammonium concentrations in soil, and consequently, in decreased ammonia volatilization losses.This report is part of a doctoral thesis by the first author.     

Control of gaseous nitrogen losses from urea applied to flooded rice soils

This paper reports field experiments designed to determine whether the two main processes responsible for nitrogen (N) loss from flooded rice (ammonia volatilization and denitrification) are independent or interdependent, and glasshouse studies which investigated the effect of soil characteristics on gaseous nitrogen loss.In the first field experiment ammonia (NH₃) loss from the floodwater was controlled using algicides, biocides, frequent pH adjustment, shade or cetyl alcohol, and the effect of these treatments on total N loss and denitrification was determined. Most treatments reduced NH₃ loss through their effects on algal growth and floodwater pH. Total gaseous N loss (54% to 35%) and NH₃ loss (20% to 1.2%) were affected similarly by individual treatments, indicating that the amount lost by denitrification was not substantially changed by any of the treatments.In a subsequent field experiment NH₃ and total N loss were again affected similarly by the treatments, but denitrification losses were very low. In control treatments with different rates of urea application, NH₃ and total N loss were each a constant proportion of the urea applied (NH₃ loss was 17% and total N loss was 24%). These results indicate that techniques which reduce NH₃ loss can be expected to reduce total gaseous N loss.The glasshouse experiment showed that gaseous N losses could be reduced by draining off the floodwater, and incorporating the urea into the 0–0.05 m soil layer before reflooding. Even with this method, losses varied widely (6–27%); losses were least from a cracking clay and greatest from a coarse sand which allowed the greatest mobility of the applied N. Incorporation of applied urea can therefore be expected to prevent losses more successfully from clay soils with high ammonium retention capacity.     

Effects of NH3 and urea on K distribution in root and rhizosphere of maize

The effects of NH₃ formed by urea hydrolysis on K distribution in maize roots and the rhizosphere were examined by electron probe x-ray microanalysis. Fresh weight of seedlings growing on calcareous soils was decreased by applying 200 ppm N as urea attributable to the inhibition of the development of root hairs and lateral roots. In the U-200 treatment, little K accumulated in the roots but K concentration in the rhizosphere soil increased. Such a pattern does not appear in roots receiving 200 ppm as ammonium sulfate or on calcareous soils with 100 ppm N as urea or with 200 ppm as urea in an acidic clay loam. The results indicate that K efflux is responsible for the growth depression and that K efflux from the high concentration of NH₃ formed when urea is hydrolysed rather than from the NH ₄ ⁺ ion. Applying K fertilizer with urea should alleviate the adverse effects of urea on plant growth on calcareous soils by improving K status of the plant and by the decrease in rhizosphere soil pH which considerably reduces NH₃ concentration. Management designed to limit pH increase during urea hydrolysis should both prevent NH₃ injury and reduced N losses.     

湿法磷酸悬浮净化制取磷酸脲的研究

对以湿法磷酸和工业尿素为原料合成磷酸脲的工艺进行了研究,探索出了较为适宜的用湿法磷酸悬浮净化法合成磷酸脲的工艺条件和生产工艺流程.通过实验,对合成磷酸脲的主要因素反应温度、反应时间、物料配比、活化剂的用量等工艺条件对产品收率及纯度的影响进行了系统的研究.得出了湿法磷酸直接合成磷酸脲的最佳工艺条件为:反应温度75℃,反应时间0.9 h,反应活化剂RX-Ⅲ用量0.15%(质量分数),尿素与湿法磷酸的物质的量比为1.05:1.为磷酸脲的工业化生产提供了理论依据.     

硫酸、氨管式反应器在尿基复合肥装置中的应用

简要介绍尿基复合肥生产技术以及国内外尿基复合肥生产状况,重点阐述辽河通达化工股份公司复合肥厂研制开发的硫酸、氨管式反应器,及其在该厂尿基复合肥装置中的应用情况。     

湿法磷酸合成磷酸脲的工艺研究

介绍了一种新型无机化工产品——磷酸脲的开发应用现状和前景及生产工艺。以湿法磷酸和工业尿素为原料,通过正交实验,研究磷酸浓度A,反应温度B,反应时间C,结晶时间D等影响因素对产品的影响,最终探索出一条合成磷酸脲的最佳途径。     

NH3 and urea in the selective catalytic reduction of NOx over oxide-supported copper catalysts

The temperature-programmed activity of a series of oxide-supported (TiO₂, Al₂O₃ and SiO₂) Cu catalysts formed from two different Cu precursors (Cu(NO₃)₂ and CuSO₄) for the selective catalytic reduction of NO_x using solutions of urea as a reductant have been determined. These activities are compared to those found using NH₃ as a reducing agent over the same catalysts in the presence of H₂O and it is found that catalysts that are active for the selective reduction of NO_x with NH₃ are inactive for its reduction using solutions of urea. Poisoning of the surface by H₂O_ads is not responsible for all of this decrease in activity and it is postulated that the urea is not hydrolysing to form NH₃ over the catalysts but rather is oxidising to form N₂ or forming passivated layers of polymeric melamine complexes on the surface. The catalysts were characterised by temperature-programmed reduction while temperature-programmed desorption and oxidation of NH₃ and temperature programmed decomposition of urea are used to characterise the interaction of both reductants with the various catalysts.     

焦化废水中NH3-N脱除研究

焦化厂废水量大,杂质多,是化工废液中亟待处理的重大环保问题。山西焦化厂与中科院山西煤化所合作研究“粉煤灰处理焦化废水”,业已在焦化厂实际应用。焦化废水经过滤、生化后再经粉煤灰处理的流程已经实施成功。处理后的水接近深度三级处理效果,成效显著,仅ＮＨ３—...     

Impact on ammonia volatilization losses of mixing KCl of high pH with urea

Ammonia volatilization associated with urea hydrolysis has been shown to be primarily associated with the pH of the soil solution and its buffering ability in the immediate zone of the fertilizer granule. Numerous studies have also shown that these losses can be reduced significantly by the addition of large amounts of KCl with the urea. Because the pH of commercial sources of potash ranges from 6.5 to 9.5, investigations were conducted to determine if the high pH of these K sources had an effect on the ammonia lost from three contrasting soils. Despite large ammonia losses (approximately 50% of N applied) and a significant reduction in loss due to the use of KCl (30%-50% reduction), the experiments showed no effect of potash pH on ammonia loss. It may be concluded that no risk of enhanced ammonia loss can be associated with the use of high-pH potash sources.     

湿法磷酸制备磷酸脲的试验研究

磷要到脲是磷酸与尿素的加合产物,通常多用ω（Ｐ２Ｏ５）〉４０％的磷酸与尿愫 反应制得,即是饲炒添加剂,又是高深度复肥,用途广。通过试验确定了用ω（Ｐ２Ｏ５为１４％的湿法磷酸以工业氯化钠脱氯后,与尿素反应制得饲９我酸脲的工艺条件。     

Fate of urea nitrogen applied to a banana crop in the wet tropics of Queensland

This paper reports a study in the wet tropics of Queensland on the fate of urea applied to a dry or wet soil surface under banana plants. The transformations of urea were followed in cylindrical microplots (10.3 cm diameter × 23 cm long), a nitrogen (N) balance was conducted in macroplots (3.85 m × 2.0 m) with ¹⁵N labelled urea, and ammonia volatilization was determined with a mass balance micrometeorological method. Most of the urea was hydrolysed within 4 days irrespective of whether the urea was applied onto dry or wet soil. The nitrification rate was slow at the beginning when the soil was dry, but increased greatly after small amounts of rain; in the 9 days after rain 20% of the N applied was converted to nitrate. In the 40 days between urea application and harvesting, the macroplots the banana plants absorbed only 15% of the applied N; at harvest the largest amounts were found in the leaves (3.4%), pseudostem (3.3%) and fruit (2.8%). Only 1% of the applied N was present in the roots. Sixty percent of the applied N was recovered in the soil and 25% was lost from the plant-soil system by either ammonia volatilization, leaching or denitrification. Direct measurements of ammonia volatilization showed that when urea was applied to dry soil, and only small amounts of rain were received, little ammonia was lost (3.2% of applied N). In contrast, when urea was applied onto wet soil, urea hydrolysis occurred immediately, ammonia was volatilized on day zero, and 17.2% of the applied N was lost by the ninth day after that application. In the latter study, although rain fell every day, the extensive canopy of banana plants reduced the rainfall reaching the fertilized area under the bananas to less than half. Thus even though 90 mm of rain fell during the volatilization study, the fertilized area did not receive sufficient water to wash the urea into the soil and prevent ammonia loss. Losses by leaching and denitrification combined amounted to 5% of the applied N.