Urea hydrolysis and transformations in coastal dune sands and soil

Summary Urea hydrolysis was studied in samples taken from a coastal sand dune succession, from uncolonized sand; the rhizosphere ofAmmophila arenaria and soil from the mature dune. Comparisons were made with urea hydrolysis in a fertile loam soil. Urea was hydrolyzed in all sand and soil samples, with complete hydrolysis occurring after 6 and 3 weeks in the rhizosphere sand and dune soil compared with only 4 days in the fertile loam. A third of the added urea, however, was still present in the uncolonized sand samples 6 weeks after the beginning of the incubation period. Urea hydrolysis broadly correlated with urease activity.The liberated NH ₄ ⁺ was oxidized to NO ₃ ^– –N in all samples. Urea stimulated the release of N from native organic matter in the two soils, but not sands, due presumably to the low organic matter content of the latter. Nitrite accumulated in the dune sands and soil, but not in the fertile loam.Although N-Serve (Nitrapyrin) had no effect on urea hydrolysis in any of the treated samples, it inhibited the nitrification of released NH ₄ ⁺ –N. The relevance of these findings to the use of urea as a fertilizer to improve plant growth and dune stabilization is commented upon.     

稀土元素对土壤中尿素水解及其水解产物行为的影响

以潮土为供试土壤进行土培试验,研究了农用稀土对同时施加的尿素在土壤中形态转化过程影响,当稀土施用量增至10mg/kg^-1烘干土以上时,土壤中尿素水解后所形成的铵态氮含量显著增加,在不同培养时间内,土壤中源自尿素的硝态氮和亚硝态氮含量随稀土施用量增加呈降低趋势;当施用量增至50mg/kg^-1烘干土时,与对照相比的降低程度达显著水平,施加稀土元素后,土壤有效氮含量明显增加,主要由于土壤铵态氮增加所致,结合土壤pH变化,表明稀土施用量高于10mg.kg^-1烘干土时,可明显延缓尿素在潮土中水解进程并抑制水解产物铵态氮的氧化,利于土训对尿素氮固持。     

Effect of phenylphosphorodiamidate on urea hydrolysis,ammonia volatilization and rice growth in an alkali soil

Summary In order to improve nitrogen recovery by rice, the effect of a urease inhibitor phenylphosphorodiamidate (PPD) on the efficiency of fertilizer urea was studied in laboratory and greenhouse. Addition of PPD to urea (5% w/w) delayed urea hydrolysis by 3 to 4 days and reduced ammonia volatilization from 45% (without PPD) to 8.5% (with PPD). Ammonia volatilization obeyed first order kinetics. Urea hydrolysis was sufficiently strongly inhibited to match the nitrification potential of the soil. N application to rice by three different modes showed that a delayed mode (4 splits) was superior to two conventional modes (3 splits) in nitrogen recovery and fertilizer efficiency since it met nitrogen requirement of plants at reproductive stage. In 2 out of 3 modes of application, there was a 14% increase (relative) in grain yields and dry matter, and 6.8% increase in N uptake efficiency on application of PPD along with urea. The results indicate that urease inhibitors like PPD can be effectively used to block urea hydrolysis, reduce ammonia volatilization losses and improve N use efficiency by rice.     

Effects of parathion and malathion on transformations of urea and ammonium sulfate nitrogen in soils

Summary A study of the effects of malathion and parathion applied at 10 and 50 g/g of soil on transformations of urea and (NH₄)₂SO₄–N in a sandy loam showed that the insecticides retarded urea hydrolysis as well as nitrification of urea and (NH₄)₂SO₄–N. At 50 parts/10⁶ rate of the insecticides, inhibition of urea hydrolysis ranged from 44 to 61% after 0.5 week and from 7 to 21% after 3 weeks of application. The insecticides inhibited the conversion of NH₄ ⁺ to NO₂ ^– without appreciably affecting the subsequent oxidation of NO₂ ^– to NO₃ ^– –N. This resulted in accumulation of higher amounts of NH₄ ⁺–N in soil samples treated with ammonium sulfate or urea N.The results suggest that transformations of urea and NH₄ ⁺ fertilizers in soils may be influenced by the amount of organophosphorus insecticide present and this may affect plant nutrition and fertilizer use.     

Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Abstract NO production and consumption rates as well as N₂O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N₂O. Under aerobic conditions untreated soil showed very low release of NO and N₂O but high consumption of NO. Fertilization with NH₄⁺ or urea stimulated both NO and N₂O production by nitrification. Addition of glucose at high soil moisture contents led to increased N₂ and N₂O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N₂O production by denitrification. The production of NO and N₂O was further stimulated at low moisture contents and after addition of glucose or NO₃⁻. Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO₃⁻. Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N₂O release.     

Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Abstract NO production and consumption rates as well as N₂O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N₂O. Under aerobic conditions untreated soil showed very low release of NO and N₂O but high consumption of NO. Fertilization with NH₄⁺ or urea stimulated both NO and N₂O production by nitrification. Addition of glucose at high soil moisture contents led to increased N₂ and N₂O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N₂O production by denitrification. The production of NO and N₂O was further stimulated at low moisture contents and after addition of glucose or NO₃⁻. Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO₃⁻. Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N₂O release.     

Nitrification and ammonia volatilisation losses from urea and dicyandiamide-treated urea in a sandy loam soil

Summary Nitrification and ammonia volatilisation losses from urea and dicyandiamide (DCD)-treated urea were studied in a sandy loam soil. Laboratory experiments indicated that 20 ppm (of soil) DCD effectively inhibited nitrification of urea over sixty days. If the urea was treated with DCD (20 ppm), ammonia emission from the soil was extended over 105 days; with urea alone, it was negligible after 15 days. A field study indicated that DCD treatment increased volatilisation losses of ammonia tremondously if urea was applied to the soil surface; these losses were minimised if the urea was placed at 5 cm depth. It would seem that nitrification inhibitors must be combined with a placement technique.     

The release,diffusion and nitrification of nitrogen in soils surrounding sulfur-coated urea granules

Summary We have compared sulfur-coated urea granules (SCU) with ammonium sulfate granules (AS) in regard to nitrogen (N) release, diffusion, nitrification and the effect of irrigation. In the experiments plastic containers were filled with six layers of soil, separated from each other by fine nylon cloths. The fertilizer granules were placed between the two central layers, and irrigation was simulated by application of tap water to the uppermost layer. Nitrogen release from the SCU was slow, and after three months, 29.5% of the applied N remained in the granules. At the end of the experiment there was a deficit of 37.1% N in the case of the AS granules, while there was virtually none with the SCU. Throughout the experiment, N from SCU remained at a relatively even level, while 95% of the N applied as AS had disappeared after irrigation. Nitrification was rapid in both cases.     

Rate of hydrolysis of urea as influenced by thiourea and pellet size

Summary Two incubation experiments and a number of field experiments were conducted to determine the effect of soil moisture tension, pellet size and addition of thiourea to urea on the rate of urea hydrolysis. In the incubation experiments at 20°C, the rate of hydrolysis of urea increased from 15 bar to 1/3 bar soil moisture tension, with the largest change (doubling) occurring from 15 bar to 7 bar moisture tension. Increasing pellet size reduced the rate of urea hydrolysis by about 12% with urea pellets weighing 0.21 g as compared to 0.01 g urea pellets after 114h. When thiourea (a metabolic inhibitor) was pelleted with urea in a ratio of two parts urea and one part thiourea, the rate of hydrolysis was halved.In a field experiment, the addition of thiourea to urea and increasing pellet size suppressed the rate of urea hydrolysis considerably for 8 days. The amount of urea hydrolyzed with urea+thiourea (21) pellets weighing 2.51 g was one-fourth of the amount of urea hydrolyzed with 0.01 g pellets of urea alone. In the other six field experiments which were set out in October, only 22% to 39% of urea +thiourea (21) was hydrolyzed at two weeks after application, while almost all of the urea was hydrolyzed when it was mixed into the soil without an inhibitor.Unter our field conditions, we would estimate that the hydrolysis of urea can be inhibited for at least one week. The inhibition of urea hydrolysis appears to be great enough that the problems encountered from the rapid hydrolysis of urea, wherever these occur, may be reduced by combined use of thiourea and either increased pellet size or band placement.     

Nitrogen leaching losses from conventional and new nitrogenous fertilizers in low-land rice culture

Summary A pot-culture experiment was conducted to assess the leaching losses of N from the conventional and new nitrogen fertilizers under low-land rice culture. Leaching losses of N were generally less than 20% of applied N with sources other than sodium nitrate and these could be reduced by blending urea with nitrification inhibitor N-Serve or coating withneem cake or by using urea super granules or slow-release N fertilizer sulphur coated urea. These new nitrogen fertilizers were more effective than urea for rice.     

土壤盐渍化对尿素与磷酸脲氨挥发的影响

氨挥发是肥料氮素损失的重要途径之一,肥料类型、土壤类型、肥料用量以及土壤全盐量均影响氨挥发损失率及挥发特征。本文采用通气法测定了磷酸脲和尿素两种肥料六个施肥量处理分别施入六个不同盐渍化程度（1.7、9.9、16.4、23.2、29.1、37.9 g/kg）的土壤后氨挥发累积状况和动力学特性,以及土壤氨挥发累积量与土壤电导值之间的相关性。结果表明：（1）在土壤总盐介于1.66 -37.9 g/kg的范围内,随着土壤含盐量增加,尿素与磷酸脲处理的氨挥发累积量显著增加;土壤含盐量对氨挥发速率有显著的促进作用。（2）各处理二次线性函数拟合的二项式系数a均为负值,表明：在不同盐渍化条件下肥料的挥发速率是随着时间增长而降低的;一次线性函数和Elovich 方程的斜率a随土壤含盐量增加而增大,表明：土壤盐渍化将加剧土壤的氨挥发速率。（3）土壤氨挥发累积量与电导值拟合结果符合logistic方程（︱R︱分别为0.9732,0.9815,0.965,0.9182,0.9817,0.9971︱R︱>r0.01=0.9172, n=6）,氨挥发累积量随土壤电导值呈“S”型增长。     

脲酶-硝化抑制剂对减缓尿素转化产物氧化及淋溶的作用

利用原状土柱模拟试验,研究了脲酶抑制剂氢醌(HQ),硝化抑制剂包被碳化钙(ECC)和双氰胺(DCD)以及它们的不同组合对尿素转化产物土壤持留、氧化以及淋溶的影响.结果表明,与其它抑制剂处理相比,HQ+DCD组合能有效抑制尿素水解产物的氧化,使其以交换态NH₄⁺的形式在土壤中长时间持留;氧化作用的抑制不仅减少了氧化产物NO₃^-的累积,也降低了NO₃^-淋溶潜势,使其淋入下层土壤的深度仅限在5～10 cm范围内,且淋溶量显著降低.     

Control of urea hydrolysis and nitrification in soil by chemicals—Prospects and problems

Summary A review is made of the recent work to assess the prospects of regulating urea hydrolysis and nitrification processes in soils by employing chemicals that can retard urea hydrolysis and nitrification. The possible benefits from control of nitrogen transformations in terms of conserving and enhancing fertilizer nitrogen efficiency for crop production and the problems associated with their use with regard to N metabolism of plants have also been discussed with examples. Prospects of using cheap and effective indigenous materials and chemicals for control of urea hydrolysis and nitrification under specific soil situations appear eminent in improving the fertilizer nitrogen efficiency. Urease inhibitors may be helpful in reducing problems associated with ammonia volatilization if this is not offset by leaching of urea. On the other hand retardation of nitrification appears useful in reducing losses that accompany nitrification due to leaching and denitrification, and with the plants that metabolize equally well with relatively higher amounts of NH₄–N may be more effective in improving the utilization of fertilizer N under these situations.     

脲酶-硝化抑制剂对减缓尿素转化产物氧化及淋溶的作用

利用原状土柱模拟试验,研究了脲酶抑制剂氢醌(HQ),硝化抑制剂包被碳化钙(ECC)和双氰胺(DCD)以及它们的不同组合对尿素转化产物土壤持留、氧化以及淋溶的影响.结果表明,与其它抑制剂处理相比,HQ+DCD组合能有效抑制尿素水解产物的氧化,使其以交换态NH₄⁺的形式在土壤中长时间持留;氧化作用的抑制不仅减少了氧化产物NO₃^-的累积,也降低了NO₃^-淋溶潜势,使其淋入下层土壤的深度仅限在5～10 cm范围内,且淋溶量显著降低.     

Labeled nitrogen fertilizer research with urea in the semi-arid tropics

Summary Field studies with bordered microplots were conducted on an Alfisol in the semiarid tropics of India to determine (1) the fate of¹⁵N-labeled urea applied to dryland sorghum in two successive rainy seasons and (2) the effect of method of application on N fertilizer efficiency. Recoveries of¹⁵N-labeled fertilizers by above-ground plant parts ranged from 46.7% to 63.6% in 1981 when the rainfall was above the average and from 54.4% to 66.9% in 1980 when the rainfall was near the average. Small (0.014 g) pellets of urea applied twice as postemergent applications in separate 5 cm deep bands were more effective than single preemergent applications either surface applied or incorporated. Both banding and the split applications contributed to overall fertilizer efficiency. Large (1.0 g) pellets of urea (supergranules) placed at a depth of 5 cm were also superior to the incorporated, small-pellet treatment in 1981. The¹⁵N-balance data for the soil (0–90 cm in depth)-plant system in 1981 showed that the unaccounted-for fertilizer N ranged from 5.1% to 20.6%. An important finding was that high grain yields, in excess of 6,000 kg/ha, with N fertilizer losses of less than 10% could be obtained through fertilizer management during a very wet season. The data from the Alfisol experiments were compared with data from similar Vertisol experiments; N fertilizer losses resulting from incorporated and surface applications were greater for Vertisols than for Alfisols in the wetter year.     

Effects of organic matter on sulphur oxidation in soil and influence of sulphur oxidation on soil nitrification

Summary The effects of wheat straw and pressed sugar beet pulp on sulphur oxidation were determined in a loam soil amended with 1% (w/w) elemental sulphur. Wheat straw stimulated the oxidation of elemental sulphur over the first 2 to 3 weeks of the incubation period, resulting in an increase in LiCl-extractable sulphate. After 4 to 7 weeks incubation however, the only significant increase in soil sulphate followed the 1% straw addition, while at week 7 sulphate concentrations in the 0.25% and 5.0% straw amended soils were lower than the control. Pressed sugar beet pulp (1% w/w) initially stimulated the oxidation of elemental sulphur in the soil, but by weeks 3 to 7 of the incubation period rates of oxidation in pulp-amended soils were lower than the control. Towards the end of the incubation period however, sulphate concentrations in the amended soils exceeded the control values, significantly so by week 11. The concentration of thiosulphate and tetrathionate also increased in soils receiving sugar beet pulp. Nitrification was inhibited in soils in which sulphur oxidation was actively occurring. Although possible alternatives are mentioned, such inhibition appears to result from a decrease in soil pH brought about by the oxidation of elemental sulphur to sulphuric acid.     

几种硝化抑制剂对土壤和小白菜硝酸盐含量及产量的影响

通过田间试验,对湖南长沙地区的红菜园土和冲积菜园土两种土壤条件下氢醌 (HQ)、双氰胺 (DCD)和硫脲 (TU) 3种硝化抑制剂对土壤和小白菜硝酸盐含量及小白菜产量的影响进行研究.结果表明,3种硝化抑制剂在试验的各个时期均不同程度地降低了土壤和小白菜的硝酸盐含量,其中以双氰胺的效果最好.但不同供试土壤条件下的试验结果不完全一致.3种硝化抑制剂均可不同程度提高小白菜产量,其中双氰胺效果最好,且在红菜园土的增产效果比冲积菜园土显著.     

农田土壤硝酸盐积累与淋失研究进展

农田土壤硝酸盐淋失是导致地下水硝酸盐污染的主要原因。影响农田土壤中硝酸盐积累的淋失的因素很多。主要有施肥、降水、灌溉、土壤性质以及耕种制度等,过量施用氮肥,不论是单独施用无机肥、有机肥还是有机、无机混施都能造成硝酸盐在土体中大量积累;耕作和种植制度均能影响硝酸盐在土体中的积累和迁移;降水和灌溉带来的下渗水流是累积在土壤中的硝酸盐向下迁移直至淋失的必要条件,也是运载工具,而土壤中的大孔隙则是下渗水流的主要通道,农田土壤硝酸盐的积累与淋失是多种因素综合作用的结果,模型是研究和预测硝酸盐淋失的理想工具,近年来发展很快,并且得到了很好的应用。     

Effect of ferrous sulphate on nitrification during simultaneous phosphorus removal from domestic wastewater using a laboratory scale anoxic/oxic reactor

In the present study a laboratory scale anoxic/oxic reactor was used to remove the important eutrophication nutrients such as phosphorus and nitrogen from synthetic domestic wastewater. Phosphorus was removed through simultaneous precipitation and was carried out using the coagulant ferrous sulphate FeSO₄ · 7H₂O. Total phosphorus in the effluent was controlled to below 1 mg/l using a ferrous to phosphorus molar ratio of 2.1. pH after the addition of coagulant plays a major role in determining the molar ratio of the precipitant. Nitrogen was removed biologically in the anoxic/oxic system and the effect of simultaneous precipitation on nitrification and denitrification was investigated. The nitrification rate of the system remained unaffected during simultaneous precipitation and varied from 0.046 to 0.059 g N–NH₄ ⁺/g VSS/day. Denitrification was complete and was not affected by the coagulation process. The nitrogen removal efficiency varied from 78% to 85%. COD removal efficiency was not affected during simultaneous precipitation and was varied from 94% to 98%. The highly efficient nitrogen removal in the presence of simultaneous precipitant ferrous sulphate makes the process an ideal option for nutrient removal.     

Leaching of Pseudomonas aeruginosa, and transconjugants containing pR68.45 through unsaturated, intact soil columns

Abstract Leaching of genetically engineered microbes (GEMs) through soil is a significant concern related to groundwater quality. The objective of this study was to examine the leaching, survival and gene transfer of a genetically engineered microbe and indigenous recipients of pR68.45 in nonsterile, undisturbed soil columns. Pseudomonas aeruginosa PAO25, containing the plasmid R68.45, was added to the surface of undisturbed soil columns (10 cm diameter × 80 cm length). Unsaturated flow conditions were maintained by 100 ml daily additions of 2 mM CaCl₂ for a period of 70 days. The population of the GEM exhibited a significant ( P = 0.05) linear decline with time. The GEM leached only to a depth of 30–40 cm in 70 days. Transfer of pR68.45 was shown to occur from P. aeruginosa into the indigenous bacterial population although relatively low numbers of transconjugants were observed (log 2 cfu g⁻¹ dry soil). The number of transconjugants also decreased with depth and time. Leaching of transconjugants, however, occured more readily than that of the GEM, probably as a result of plasmid transfer into smaller, more mobile bacteria. At 70 days incubation, no GEMs were detected in the columns, while transconjugants were observed at several depths. These results demonstrate the importance of examining both the survival and movement of GEMs and transconjugants in soil.