Nitrous oxide emission as affected by changes in soil water content and nitrogen fertilization

Nitrous oxide emission was measured in laboratory incubations of an alluvial soil (58% clay, pH 7.4). The soil was amended with 40 mg N kg⁻¹ as NaNO₃ or NH₄Cl, or with NaCl as a control. Each fertilization treatment was adjusted to three different water contents: constant 60% WHC (water-holding capacity), constant 120% WHC, and water content alternating between 60 and 120% WHC. During an 8-day incubation period N₂O emission rates and inorganic nitrogen concentrations in soil (NH₄⁺, NO₂⁻, NO₃⁻) were determined at regular intervals. In the control and after nitrate application small N₂O emission rates occurred with only minor variations over time, and no differences between the water treatments. In contrast, with ammonium application N₂O emission rates were much higher during the first two days of incubation, with peaks in the constant 60% WHC and 120% WHC at day 1 and in the changing-water treatment at day 2, when the first wet period (120% WHC) was completed. This N₂O peak in the changing-water treatment was 4 to 9 times higher than with constant WHC and occurred when both, NH₄⁺ and NO₂⁻ concentrations declined sharply. Thus, this N₂O emission flush can be attributed to nitrifier denitrification. After the second rewetting of the NH₄⁺-amended soil no further N₂O emission peak was observed, being in accordance with small NH₄⁺ and NO₂⁻ concentrations in soil at that time. The unexpectedly small N₂O fluxes in the constant 120% WHC treatment after nitrate application were probably caused by the reduction of N₂O to N₂ under the prevailing conditions. It can be concluded that continuous wetting or flooding of a soil is an effective measure to reduce N₂O emissions immediately after the application of NH₄⁺ fertilizers.     

Effect of residence time on the kinetics of nonexchangeable ammonium release from illite and vermiculite

The fraction of nonexchangeable ammonium (NH₄⁺) can play an important role in N cycling of soils as a sink (fixation) or a source (release) of NH₄⁺. Recently fixed nonexchangeable NH₄⁺ especially seems to be a significant source for N release. The aim of our study was to determine the effect of residence time on the kinetics of nonexchangeable NH₄⁺ release from illite and vermiculite. Calcium-saturated illite and vermiculite, containing NH₄⁺ that was “fixed” for one and 60 d, were extracted with a H-resin for 0.25 to 384 h. Both clay minerals “fixed” significantly more NH₄⁺ in 60 d than in 1 d, but vermiculite “fixed” more NH₄⁺ than illite. The kinetics of nonexchangeable NH₄⁺ release from illite and vermiculite were well described by the Elovich equation and by a heterogeneous diffusion model. In vermiculite the percentage of nonexchangeable NH₄⁺ release decreased from 84% to 78% when the time of fixation increased from 1 to 60 d. In illite time of residence has not influenced the complete release of newly fixed NH₄⁺.     

膨润土防渗毯用于渠道衬砌及其老化因素对力学性能的影响

膨润土防水毯(GCL)在渠道衬砌工程有较大的应用价值.为了测试膨润土防渗毯用于渠道衬砌其老化因素对力学性能的影响,以内蒙古河套灌区为研究区域,采用室内模拟及工程现场试验相结合,对5种老化因素的3种GCL力学性能影响进行了测试.结果表明:温度、湿度、紫外线照射都会对GCL的力学性能造成影响.高温对GCL力学性能影响大于低...     

黏土对沙地土壤改良效果的微形态研究——以内蒙古科尔沁沙地为例

为了研究施加黏土后的沙地土壤微形态特征,说明其改良效果,对内蒙古科尔沁沙地土壤切片进行观察,并利用土壤切片图像处理分析系统和Image-Pro Plus 6.0软件进行处理和分析,提取基质、孔隙和粗骨颗粒等和土壤肥力状况相关的定量化数据进行分析及定性分析,结果表明:施加黏土后,出现了块状微结构和雏形团聚体;从基质比、毛管孔隙占比方面来说,底施处理效果更好,基质比在C2(3×10~5 kg/hm~2)处理水平比对照组提高了8.8%,毛管孔隙占比在C3(6×10~5kg/hm~2)处理水平提高了15%;就总孔隙百分比、粗骨颗粒磨圆度、粉粒百分比、粗骨颗粒平均粒径来说,表施处理效果比较好,C1(1.5×10~5 kg/hm~2)、C2(3×10~5 kg/hm~2)处理水平均有显著改善。结论:1)施加黏土后,沙地土壤结构与原始沙地的粒状微结构相比有一定的改善;2)短期底施处理下,C1和C2处理单元的基质比有所提高,毛管孔隙占比随着黏土施加量的增加而提高;粗骨颗粒特征方面,表施处理效果比底施效果要好;3)短期改良情况下,沙地土壤微结构并没有太大的变化,还是以粗骨颗粒为主,但改良后出现一些雏形团聚体,各量化指标均有不同程度的提高。     

水平荷载作用下斜坡刚性桩非线性分析

在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。     

一种新型可控黏土复合膏浆在动水地层防渗中的应用

[目的]研究一种新型可控黏土复合膏浆在动水地层中的防渗应用,治理岩溶地区的水库堤坝渗漏以及大量架空结构的土(堆)石围堰的渗漏问题等。[方法]采用试验的方法,研究掺入新型外加剂具有流动度低,凝结时间可控以及良好的抗水流冲释能力的复合膏浆在动水地层的防渗堵漏效果。[结果]使用固化剂和速凝剂,其掺入量对膏浆的抗水流冲释能力、初凝时间以及流动度均有显著影响,从而可以通过固化剂和速凝剂掺入量的不同来有效的调节复合膏浆的物理力学性质,使其达到工程要求。[结论]采用此种可控黏土复合膏浆处理含有强透水砂卵石的动水地层的渗漏问题,可以使渗漏地层的防渗能力有效地大幅度提高,处理效果显著。     

冻结气温降幅对潜水入流量影响的试验研究

为了揭示冻结气温降幅对潜水入流量的影响,通过室内冻结试验装置设定地下水位埋深为87.5 cm,进行了3种冻结气温降幅,2种土壤质地的单向土壤冻结试验,监测潜水入流量的变化。结果表明：大幅降温冻结下,潜水入流速率较大,冻结第41天砂壤土和粉质粘壤土潜水入流量分别较小幅降温冻结下的潜水入流量高51.8 mm和50.7 mm;冻结气温降幅越大,潜水入流量受土壤质地的影响越明显,小幅降温、中幅降温和大幅降温冻结下,第41天砂壤土潜水入流量较粉质粘壤土潜水入流量分别高8.6 mm、11.5 mm和14.2 mm;土壤颗粒直径越小,潜水入流量对冻结气温降幅的响应越早。研究成果对于地下水浅埋区地下水资源量的科学评价和土壤盐碱化防治等具有重要的指导意义。     

Organic‐carbon fractions in an agricultural topsoil assessed by the determination of the soil mineral surface area

According to recent conceptual models, the organic carbon (OC) of soils can be divided into OC fractions of increasing stability from labile free OC to resistant OC associated with the soil mineral phase. In this study, we present a method for quantifying two OC fractions based on soil aggregate–size fractionation and the N₂ gas–adsorption method. For this purpose, we analyzed soil material of the plow layer of a Haplic Chernozem subjected to different fertilizer treatments (no fertilizer, mineral fertilizer, mineral and organic fertilizer). The total organic‐C concentration (TOC) and the clay content of the different size fractions were determined as well as the specific surface area (SSA_mineral) and the sample pore volume after thermal oxidation (OC‐free). The TOC of the different soil‐aggregate fractions was linearly related to SSA_mineral. Clay‐associated OC and nonassociated OC fractions of the different soil samples were quantified using two methods based on the OC surface loading at the clay fraction. The application of organic fertilizer increased the amount of nonassociated OC but hardly affected the concentration of clay‐associated OC. This finding agrees with previous studies on C dynamics in soils and indicates a finite capacity of soil materials to sequester OC. Even without any addition of organic fertilizer, the mineral phase of the analyzed soil material appears to be C‐saturated.     

耕作方式对Brookston粘壤土耕层不同深度有机碳分布及稳定性影响

以加拿大安大略省西南部的Brookston粘壤土为研究对象,测定免耕和秋翻管理下耕层土壤不同深度(0～5,5～10,10～20 cm)中土壤有机碳的分布与动态变化,探索耕作方式对耕层不同深度中有机碳数量与稳定性的影响.结果表明:表层(O～5 cm)中,长期免耕土壤有机碳含量高于长期秋翻和短期免耕土壤,且有机碳较容易矿化,更加活跃.下层(10～20 cm)中,长期免耕土壤有机碳含量低干长期秋翻和短期免耕土壤,有机碳稳定性高于长期秋翻和短期免耕土壤.     

不同质地土壤主要养分动态变化及其对烤烟的影响分析

研究不同质地贵州黄壤主要养分在烤烟生长发育周期内的动态变化及其对烟叶产量、品质的影响.将威宁粉壤土、开阳壤粘土同置于开阳气候下,采用统一栽培措施种植烤烟.研究发现,与高等肥力的壤粘土比较,中等肥力的粉壤土矿化率更高,无机氮、有效磷含量更高,利于保存施入的铵态氮,烟叶氮素、钾素浓度更大,烟叶钾氯比更大,烟叶产量更高.而高...