硼砂对灰棕紫泥土尿素转化与脲酶活性的影响

采用室内培养,连续取样测定培养期内0%、0.5%、1%、1.5%和2%的硼砂对灰棕紫泥土中尿素、铵态氮、硝态氮和脲酶活性变化的影响。结果表明,硼砂能抑制脲酶活性,进而减缓尿素水解速度与铵态氮释放速度,0.5%的硼砂效果较弱,随硼砂用量的增大,效果增强;硼砂对硝态氮的积累影响不大。由于硼本身就是作物必需营养元素,因此作为尿素缓释剂有着良好的应用前景。     

杀灭菊酯对亚热带果园红壤脲酶活性的生态毒理效应

通过模拟方法,系统研究杀灭菊酯对亚热带果园红壤脲酶活性的影响。结果表明:杀灭菊酯对土壤脲酶活性表现出先激活后抑制趋势,处理前3 d土壤脲酶活性升高,处理3 d后土壤脲酶活性受到抑制,7 d后低于对照水平;激活、抑制程度与处理浓度呈正相关。底物(尿素)浓度饱和前,土壤脲酶活性随尿素浓度增加而升高。模型U=β0 β1×C能较好拟合土壤脲酶活性(U)和尿素浓度(C)、杀灭菊酯浓度(C)之间关系,揭示出土壤酶促反应过程存在吸附-解吸的机制,证实不同肥力土壤脲酶活性受杀灭菊酯影响差异较大,高肥力土壤对土壤脲酶活性具有一定的缓冲作用,受杀灭菊酯影响较小。     

Effect of soil on urease inhibition by substituted urea herbicides

The effects of some substituted urea herbicides, fenuron, monuron, diuron and linuron, on soil urease were investigated. All herbicides are soil urease mixed inhibitors and the same inhibition mechanism is presumed. A kinetic relationship, which takes into account herbicide adsorption, is developed in order to calculate the inhibition constants of soil urease from adsorption constants. A linear relationship between Hammett sigma values and log K_i for fenuron, monuron and diuron is obtained, from which the formation of a complex between herbicides and enzyme is proposed By comparing kinetic constants for soil urease with those obtained for jack bean, in the presence of the same herbicides, a possible effect of the soil matrix on the enzyme-herbicide complex is also suggested.     

Residual effect of urea and herbicides on hexosamine content and urease and proteinase activities in a grassland soil

Urea (100 and 200 kg N/ha) and the herbicides dalapon (10 kg a.i./ha) and paraquat (3.75 kg a.i./ha) were applied to a natural grassland sward growing on an oxisol (pH 5.9) to bring about herbage renovation. During the following 18 months, there appeared to be a natural increase in the hexosamine content of the untreated soil and an increase of 71–93 per cent in the treated soil. Soil enzymes were influenced both by urea and the herbicides. Urease activity was increased by 67–79 per cent by urea and the herbicides applied separately or in combination. In contrast, both urea and dalapon decreased proteinase activity by 13–18 per cent. Urea and the herbicides together accentuated the decrease in proteinase activity by 41–56 per cent.     

The effect of nickel supply on bulb yield,urease and glutamine synthetase activity and concentrations of urea,amino acids and nitrogen of urea-fed onion plants

The role of nickel (Ni) on urea metabolism of certain plants has been documented, but little is known regarding the growth and physiological response of onion to Ni nutrition, particularly when urea is used as nitrogen source. In this research study, we investigated the effects of Ni on urea metabolism and growth of two onion cultivars (Allium cepa L., cvs. Dorrcheh and Cebolla Valenciana) supplied with urea as nitrogen source. Three levels of Ni (0, 25, and 50 µM) were used in the form of NiCl₂ or Ni-histidine [Ni(His)₂] complex. Addition of Ni positively affected nitrogen metabolism in onion plants fed with urea and thus was correlated with increase of the bulb yield. Regardless of the plant cultivar and the applied Ni source [NiCl₂ or Ni(His)₂ complex], an increase in urease activity and reduction in bulb urea concentration was observed by Ni nutrition. An increase in hydrolysis of urea and production of NH₄⁺ in the presence of Ni was correlated with higher concentration of the total amino acids (AAs) and nitrogen in onion bulbs. The efficiency of Ni(His)₂ complex in improving Ni uptake and increasing activity of urease and glutamine synthetase, two enzymes involved in urea metabolism, was in general greater than NiCl₂. Accordingly, higher concentration of AAs was measured in the onion plants supplied with Ni(His)₂ complex than those supplied with NiCl₂.     

The effect of pH upon the copper and cupric ion concentrations in soil solutions

Soil samples whose pH had been adjusted to between 4.5 and 7.5 either for long periods in the field or short periods in the laboratory were incubated after wetting with water or 0.01 m CaCl₂. Copper concentrations in the soil solutions decreased only slightly as the solution pH increased, but free cupric ion concentrations decreased considerably. The copper concentrations were smaller and the proportion of copper present in solution as cupric ion at a given pH was larger when CaCl₂ rather than water was used. Complexed organic species made up most of the copper in all solutions. The duration of pH adjustment did not affect these results. Copper adsorption isotherms were determined on the soils using low equilibrium solution concentrations. As a given copper concentration the quantity of copper adsorbed increased and the proportion of copper in solution present as cupric ion decreased with pH increase; again the duration of pH adjustment did not affect the results.     

Effect of organic matter and urease inhibitors on urea hydrolysis and immobilization of urea nitrogen in an alkaline soil

Summary Laboratory incubation experiments with ¹⁵N-labelled urea were conducted on a Aquic Udifluvent Belgian soil amended with barley straw, in, order to study the influence of three urease inhibitors, hydroquinone, phenyl phosphorodiamidate and N-(n-butyl) phosphorothioic triamide on urea hydrolysis and N transformations. The results demonstrated that the urea was hydrolyzed more rapidly when the soil was amended with ground barley straw. A pronounced inhibition of urease inhibitors occurred with the urea hydrolysis, but it was decreased by increasing the soil organic C content. A severe N immobilization (about 82–100% of the applied urea) occurred in soil samples that were rich in organic C. The addition of urease inhibitors increased urea-N immobilization by 5–30%. N-(n-butyl) phosphorothioic triamide had a stronger effect than the other two inhibitors when they were applied at the rate of 1%. However, the inhibitors decreased N immobilization when the soil was amended with barley straw.     

Conductimetric determination of soil urease activity

Abstract

A fast and sensitive method to determine urease activity in soils is described. It involves extraction of NH₄‐N with 1 N. KC1 : 0.01 N HC1 and measurement of NH₄ concentration by electroconductivity using a steady state flow system across a membrane. Sampling was done directly from the extracts with an automatic sampler at 40 samples per hour. The detection limit for NH₄‐N was below 0.05 ppm in the extract. Extracts could be stored at room temperature for 17 hours before measuring NH₄. No post‐treatment hydrolysis of urea occured.     

碘甲烷熏蒸对土壤脲酶活性的影响

溴甲烷是一种高效、广谱熏蒸剂,用于土壤消毒可有效杀灭土壤中的真菌、细菌、病毒、线虫、啮齿动物和杂草[1,2].     

包膜尿素与普通尿素掺混施用方式对土壤脲酶及春玉米生长的影响

采用大田试验,以不施氮为对照,采用释放期为60 d的包膜控释尿素(30%)与普通尿素(70%)掺混,研究了其不同施用方式(侧施、底施、分层施)对土壤脲酶及春玉米叶片净光合速率、保护酶活性的影响。结果表明:相同施氮水平下,底施处理0~40 cm土壤脲酶活性显著高于侧施和CK,尤其是在春玉米抽雄、灌浆期,但底施与分层施处理间没有显著差异。其中0~20 cm土层底施处理脲酶均值高于分层施、侧施和CK,分别为4.03%、55.94%和58.01%;20~40 cm土层底施处理脲酶均值高于分层施、侧施和CK,分别为3.77%、57.07%和67.37%。各处理植株和籽粒全氮含量变化趋势也基本一致,均表现为底施分层施侧施CK。采用底施处理在抽雄与灌浆期较分层施、侧施和CK叶片净光合速率平均值分别高3.61%、11.42%和33.43%,同时底施还提高了叶片超氧化物岐化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)活性。与分层施、侧施、CK相比,采用包膜尿素与普通尿素掺混底施春玉米产量分别增加0.42%、5.81%、49.23%。采用包膜控释尿素与普通尿素掺混底施效果明显且减少成本,是适宜北京地区推广的施用方式。     

The effect of pH on the total and free ionic concentrations of mnganese, zinc and cobalt in soil solutions

Samples of five soils whose pH in the field had been adjusted to between 5.0 and 7.5 were incubated with water or 0.01 m CaCl₂ at 90% field capacity. Additional samples of the most acid soil were limed to various pH values immediately before incubation. Manganese, zinc and cobalt concentrations in the soil solutions, collected by displacement, decreased as the pH increased; the concentrations in calcium chloride solutions were higher than those in water solutions. The free divalent ions Mn²+, Zn²+ and Co²+ were the major metal species in solution at pH 5 but the proportion of the metals present as the free ion decreased as the pH increased. Differences in the manganese and zinc concentrations in the solutions were due not only to the pH of these solutions but also to the original pH of the soil in the field.     

Influence of soil properties on urease activity under different agro-ecosystems

Urease activity (by buffer and non-buffer method) of soils of different agro-ecosystems in alluvial soil was studied. Urease activity by buffer method records a higher value than the non-buffer method. Both the methods showed significant positive correlation (0.99**) between each other. Urease activity by both methods showed positive correlation with organic matter (0.88** and 0.89**, buffer method) and clay content (0.91** and 0.83*, non-buffer method)) of the soils. Multiple regression analysis showed that the stabilization of urease activity in the soils studied was due to an organic matter?–?enzyme complex. Among the organic matter humus C plays a dominating role to control the urease activity of the soils.     

Scale-dependent relationships between soil organic carbon and urease activity

Many soil properties and processes vary at different spatial scales. As a result, relationships between soil properties often depend on scale. In this paper we show this for two soil properties of biological importance, by means of a nested analysis of covariance. The variables were urease activity (UA) and soil organic carbon (SOC), sampled on an unbalanced nested design at three sites with different land uses (arable, forest and pasture). The objective of this study was to investigate the scale‐dependent relationships of UA and SOC at these three sites to exemplify the phenomenon of scale‐dependency in the covariation of biogeochemical variables. At each site the variables showed different scale dependencies, expressed in their correlations at different scales. At the pasture site, UA and SOC were uncorrelated at all scales in the sampling design (0.2 m, 1 m, 6 m and ≥15 m), and the overall product moment correlation was 0.10. A significant positive scale dependent correlation (0.65) was found at the 1‐m scale for the forested site. The soil properties were not spatially correlated at any of the other scales and the associated product moment correlation for this site was 0.14. Urease activity and soil organic C were found not to be correlated at the shorter scales in the arable site. However, significant positive correlation coefficients of 0.89 and 0.82 were obtained at the longer scales of 6 and ≥15‐m respectively for the arable site. The product moment correlation at this site was 0.65. At both the arable and forest site, we found that correlations at particular scales were stronger than the overall product moment correlation. This approach allowed us to identify significant relationships between urease activity and soil organic carbon and the scales at which these relationships occur and to draw conclusions about the spatial scales, which must be resolved in further studies of these variables in these contrasting environments. This study highlights the pervasive effect of scale in soil biogeochemistry and shows that scale‐dependence must not be disregarded by soil scientists in their investigations of biogeochemical processes.     

The effect of phenyl phosphorodiamidate on urease activity and ammonia volatilization in flooded rice

Summary The behaviour of urease activity, ammoniacal N concentrations and pH in flood water and that of ammonia flux was investigated in a water-logged soil either in the presence or in the absence of rice and with three different treatments (control, urea and urea + phenyl phosphorodiamidate). In the presence of the phenyl phosphorodiamidate (PPD), that is a urease inhibitor, increases in ammoniacal N concentrations and in ammonia evolution were delayed but not eliminated. The degradation and/or the inactivation of PPD might have occurred, thus removing the inhibition of the enzyme activity.     

应用几种植物物质及化合物抑制土壤脲酶活性和提高植物尿素氮的回收率

Effects of residues of 9 plants, lemon eucalyptus (Eucalyptus citriodora Hook., P1), robust eucalyptus (E. robusta Smith, P2), Nepal camphortree (Cinnamomum glanduliferum (Wall.) Nees, P3), tea (Camellia sinensis (Linn.) O. Ktze. f., P4), oleander (Nerium indicum Mill, P5), rape (Brassica campestris L., P6),Chinese tallow tree (Sapium sebiferum L., P7), tung (Vernicia fordii (Hemsl.), P8), and croton (Croton tiglium L., P9), 7 chemicals, boric acid (C1), borax (C2), oxalic acid (C3), sodium oxalite (C4), sodium dihydrogen phosphate (C6), sodium silicate (C7) and sodium citrate (C8), and a natural organic substance,humic acid (C5), on urease activity of a neutral purple soil and recovery of urea nitrogen by maize were studied through incubation and pot experiments. Hydroquinone (HQ) was applied as the reference inhibitor. After incubation at 37 ℃ for 24 h, 7 inhibitors with higher ability to inhibit urease activity were selected and then incubated for 14 days at 25 ℃. Results of the incubation experiments showed that soil urease activity was greatly inhibited by them, and the inhibition effect followed an order of P2＞P4＞C3＞C2＞P3＞C1＞HQ＞P1.The 7 selected materials reduced the accumulative amounts of N released from urea and the maximum urease activity by 11.7%～28.4% and 26.7%～39.7%, respectively, and postponed the N release peak by 2～4 days in the incubation period of 14 days under constant temperature, as compared to the control (no inhibitor).In the pot experiment with the 7 materials at two levels of addition, low (L) and high (H), the C1 (H), C3(H), C1 (L), P4 (L) and C2 (L) treatments could significantly increase the dry weights of the aboveground parts and the total biomass of the maize plants and the apparent recovery rate of urea-N was increased by 6.3%～32.4% as compared to the control (no hibitor).     

Synthesis of organo-montmorillonite and its effect on soil urease and L-glutaminase activites

Organoclays are highly important to environmental studies due to their unique applications. The amidohydrolase family plays a significant role in maintaining a sustainable environment and agriculture sector. Therefore, keeping these enzymes active and stable in soil is a crucial task. In doing so, this study focused on the synthesis of organo-montmorillonite (MMT) and its effect on activity and stability of these enzymes in soil. The organo-MMT was synthesized by modifying the Na-MMT using the HDTMA-Br Cationic surfactant. Mineralogical properties of the synthesized organoclay were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscope (FESEM) instruments. The effects of this organoclay and incubation period on urease and L-glutaminase activities in soil were also investigated. Results showed that the d-spacing of organo-MMT was increased by adding surfactant. Results from statistical analyses showed that the effect of clay type and incubation period on the activity of both enzymes (urease and L-glutaminase) were significant at the 5% level. The activity of both enzymes in the soil samples treated with the organo-MMT was significantly higher than control and MMT samples. The organoclay prepared successfully maintained soil enzymes. Therefore, use of this organoclay can positively affect enzyme activity and stability. This study plays an important role in synthesizing low-cost organoclays to be used in increasing the stability and activity of amidohydrolase family in soil.     

四川茶园土壤中脲酶活性研究

用苯酚一次氯酸钠比色法,分析了四川几种主要茶园土壤脲酶活性状况.结果表明,在同一时期,不同种类茶园土壤中脲酶活性差异较大;随着季节的不同,土壤中脲酶活性也有较大变化;同时,在不同的土层中,其脲酶活性也表现出不一样.另经相关分析,土壤中脲酶活性与全氮、有机质、速效氮等关系密切.     

Effects of urease and nitrification inhibitors added to urea on nitrous oxide emissions from a loess soil

Urea fertilizer‐induced N₂O emissions from soils might be reduced by the addition of urease and nitrification inhibitors. Here, we investigated the effect of urea granule (2–3 mm) added with a new urease inhibitor, a nitrification inhibitor, and with a combined urease inhibitor and nitrification inhibitor on N₂O emissions. For comparison, the urea granules supplied with or without inhibitors were also used to prepare corresponding supergranules. The pot experiments without vegetation were conducted with a loess soil at (20 ± 2)°C and 67% water‐filled pore space. Urea was added at a dose of 86 kg N ha^–1 by surface application, by soil mixing of prills (<1 mm) and granules, and by point‐placement of supergranules (10 mm) at 5 cm soil depth. A second experiment was conducted with spring wheat grown for 70 d in a greenhouse. The second experiment included the application of urea prills and granules mixed with soil, the point‐placement of supergranules and the addition of the urease inhibitor, and the combined urease plus nitrification inhibitors at 88 kg N ha^–1. In both experiments, maximum emissions of N₂O appeared within 2 weeks after fertilization. In the pot experiments, N₂O emissions after surface application of urea were less (0.45% to 0.48% of total fertilization) than from the application followed by mixing of the soil (0.54% to 1.14%). The N₂O emissions from the point‐placed‐supergranule treatment amounted to 0.64% of total fertilization. In the pot experiment, the addition of the combined urease plus nitrification inhibitors, nitrification inhibitor, and urease inhibitor reduced N₂O emissions by 79% to 87%, 81% to 83%, and 15% to 46%, respectively, at any size of urea application. Also, the N₂O emissions from the surface application of the urease‐inhibitor treatment exceeded those of the granules mixed with soil and the point‐placed‐supergranule treatments receiving no inhibitors by 32% to 40%. In the wheat growth experiment, the N₂O losses were generally smaller, ranging from 0.16% to 0.27% of the total fertilization, than in the pot experiment, and the application of the urease inhibitor and the combined urease plus nitrification inhibitors decreased N₂O emissions by 23% to 59%. The point‐placed urea supergranule without inhibitors delayed N₂O emissions up to 7 weeks but resulted in slightly higher emissions than application of the urease inhibitor and the urease plus nitrification inhibitors under cropped conditions. Our results imply that the application of urea fertilizer added with the combined urease and nitrification inhibitors can substantially reduce N₂O emissions.     

Effect of urease inhibitors on urea hydrolysis and ammonia volatilization

Summary Two laboratory incubation experiments were conducted to study the effects of the urease inhibitors hydroquinone (HQ), phenyl phosphorodiamidate (PPDA), and N-(n-butyl) thiophosphoric triamide (NBPT) in retarding the hydrolysis of urea, in the evolution of mineral N, and in reducing NH₃ loss through volatilization, under aerobic and waterlogged conditions, both at 25°C. NBPT generally exceeded PPDA and HQ in the ability to delay urea hydrolysis and NH _inf4 ^sup+ accumulation under aerobic conditions, whereas PPDA retarded these activities more effectively under anaerobic conditions. HQ was less effective than the other two urease inhibitors. Under aerobic conditions, 20% of the applied urea was lost through NH₃ volatilization after 5 days in the system without an inhibitor. With the addition of HQ and PPDA, the volatilization was delayed by 1 day but not eliminated. NBPT effectively decreased the NH₃ loss, from 20 to 3% of the applied urea. A more severe N loss (40%) occurred in the waterlogged system. HQ had little effect on NH₃ volatilization. PPDA decreased the NH₃ loss from 40 to less than 20% of the applied urea. The effectiveness of NBPT decreased under anaerobic conditions. It was concluded that urease inhibitors can reduce NH₃ volatilization following the application of urea. However, environmental conditions might have an important influence on the effectiveness of these inhibitors.