定期淹水强碱性盐渍土中14C标记葡萄糖和NH4+的动态

Flooding an extremely alkaline（pH 10.6） saline soil of the former Lake Texcoco to reduce salinity will affect the soil carbon（C）and nitrogen（N） dynamics.A laboratory incubation experiment was done to investigate how decreasing soil salt content affected dynamics of C and N in an extremely alkaline saline soil.Sieved soil with electrical conductivity（EC） of 59.2 dS m^-1 was packed in columns,and then flooded with tap water,drained freely and conditioned aerobically at 50%water holding capacity for a month.This process of flooding-drainage-conditioning was repeated eight times.The original soil and the soil that had undergone one,two,four and eight flooding-drainage-conditioning cycles were amended with 1000 mg glucose-¹⁴C kg^-1 soil and 200 mg NH₄⁺-N kg^-1soil,and then incubated for 28 d.The CO₂ emissions,soil microbial biomass,and soil ammonium（NE₄⁺）,nitrite（NO₂^-） and nitrate（NO₃^-） were monitored in the aerobic incubation of 28 d.The soil EC decreased from 59.2 to 1.0 dS m_¹ after eight floodings,and soil pH decreased from 10.6 to 9.6.Of the added ¹⁴C-labelled glucose,only 8%was mineralized in the original soil,while 24%in the soil flooded eight times during the 28-d incubation.The priming effect was on average 278 mg C kg^-1 soil after the 28-d incubation.Soil microbial biomass C(mean 66 mg C kg^-1 soil) did not change with flooding times in the unamended soil,and increased 1.4 times in the glucose-NH₄⁺-amended soil.Ammonium immobilization and NO₂^- concentration in the aerobically incubated soil decreased with increasing flooding times,while NO₃^- concentration increased.It was found that flooding the Texcoco soil decreased the EC sharply,increased mineralization of glucose,stimulated nitrification,and reduced immobilization of inorganic N,but did not affect soil microbial biomass C.     

近场波束形成声源识别的改进算法

为提高近场波束形成方法的声源识别性能和阵列平面上最大声压贡献量的计算精度,首先基于球面波假设,采用除自谱的互谱波束形成算法,仿真分析了阵列传声器信号幅值校正对声学成像和声源识别的影响,结果表明:幅值的校正在提高阵列平面上最大声压贡献量计算精度的同时也带来了旁瓣水平增大,动态范围缩小等诸多不足.在此基础上,提出并设计了声源定位与强度幅值校正相结合的近场波束形成阵列平面卢压贡献量的改进算法,仿真分析与算例试验结果均表明:改进算法既能准确计算阵列平面上的最大声压贡献量,且旁瓣水平低,声源成像动态范围增大1.0～1.6dB.最后,利用改进算法进行了某车的声学密封性能试验,准确识别了该车的声学密封薄弱位置.     

N2O fluxes from a Haplic Luvisol under intensive production of lettuce and cauliflower as affected by different N‐fertilization strategies

Vegetable‐production systems often show high soil mineral‐N contents and, thus, are potential sources for the release of the climate‐relevant trace gas N₂O from soils. Despite numerous investigations on N₂O fluxes, information on the impact of vegetable‐production systems on N₂O emissions in regions with winter frost is still rare. This present study aimed at measuring the annual N₂O emissions and the total yield of a lettuce–cauliflower rotation at different fertilization rates on a Haplic Luvisol in a region exposed to winter frost (S Germany). We measured N₂O emissions from plots fertilized with 0, 319, 401, and 528 kg N ha^–1 (where the latter three amounts represented a strongly reduced N‐fertilization strategy, a target value system [TVS] in Germany, and the N amount fertilized under good agricultural practices). The N₂O release from the treatments was 2.3, 5.7, 8.8, and 10.6 kg N₂O‐N ha^–1 y^–1, respectively. The corresponding emission factors calculated on the basis of the total N input ranged between 1.3% and 1.6%. Winter emission accounted for 45% of the annual emissions, and a major part occurred after the incorporation of cauliflower residues. The annual N₂O emission was positively correlated with the nitrate content of the top soil (0–25 cm) and with the N surpluses of the N balance. Reducing the amount of N fertilizer applied significantly reduced N₂O fluxes. Since there was no significant effect on yields if fertilization was reduced from 528 kg N ha^–1 according to “good agricultural practice” to 401 kg N ha^–1 determined by the TVS, we recommend this optimized fertilization strategy.     

Soil respiration across three contrasting ecosystem types: comparison of two portable IRGA systems

An accurate assessment of soil respiration is critical for understanding and predicting ecosystem responses to anthropogenic perturbation such as climate change, pollution, and agriculture. Infra‐red gas analyzer (IRGA)–based field measurement is the most widely used technique for assessing soil‐respiration flux rates. In this study, respiration rates obtained with two common IRGA systems (LI‐COR 8100 and PP Systems EGM‐4) were compared across three ecosystem types. Our results showed that both methods were highly comparable in their flux estimates, but the associated methodology used (notably the use or absence of a soil collar) resulted in greater uncertainty in flux rates and a greater degree of intrasite variation. Specifically, the use of collars significantly decreased the flux estimate for both IRGAs compared to the no‐collar estimate. The disturbance caused by collar insertion was assumed to be a major factor in causing the differing flux estimates, with root and mycorrhizal severance likely being the main contributor. We conclude that the two IRGAs used in this study can be reliably compared for overall flux estimates but emphasis is needed to validate a common measurement methodology.     

节水灌溉对稻田N2O季节排放特征的影响

为了揭示节水灌溉对技术对稻田N2O排放的影响,采用静态暗箱-气相色谱法对稻田N2O排放进行了田间原位观测,分析了节水灌溉对稻田N2O季节排放特征的影响。结果表明,水稻全生育期节水灌溉稻田N2O平均排放通量为41.84 μg/(m2 ?h),较淹水灌溉稻田N2O平均排放通量增加了33.3%;节水灌溉稻田N2O排放总量为119.86 mg/m2,比淹水灌溉稻田显著增加了17.8%;节水灌溉稻田N2O排放通量呈现明显的季节变化规律,有两次较大的排放峰值,峰值主要出现在施肥后1周左右;节水灌溉稻田土壤的每次脱水过程均不同程度地加剧了N2O排放,复水后N2O排放通量有增有减但变幅不大,而淹水灌溉稻田在黄熟期落干阶段N2O排放出现反弹。由此可见,不同灌溉模式下的稻田土壤水分状况决定了N2O季节排放的差异,与淹水灌溉相比,控制灌溉显著增加了稻田N2O季节排放量。     

华北平原典型农田CO2和N2O排放通量及其与土壤养分动态和施肥的关系

对华北平原小麦-棉花(麦棉)、小麦-大豆(麦豆)、小麦-玉米(麦玉)轮作田的CO2和N2O排放通量进行了测定,分析了温室气体排放通量与土壤中碳、氮元素、气温以及施肥等之间的关系。主要结论:1)麦棉、麦豆、麦玉田的土壤CO2平均排放通量分别为CO2-C 141.7、109.8、128.2 mg.m-2.h-1,其中夏播作物的排放通量高于小麦季;2)麦棉、麦豆及麦玉田作物生长季的土壤N2O平均排放通量分别为N2O-N 98.8、38.9、44.7μg.m-2.h-1,也表现为麦后季作物的排放量高于小麦季;3)同一生育期中不同处理的N2O排放主要与土壤中无机氮含量相关,不同生育期的N2O排放通量主要受不同生育期的土壤温度及水分状况的影响;4)在施肥灌溉后的9 d内土壤N2O排放通量较高,之后逐渐降低,至施肥后22～27 d即与不施肥处理的排放持平。     

Hilbert-Huang transform and denoising for partial discharge ultrsonic singals of large motor

Empirical mode decomposition (EMD) algorithm is introduded as the core of the Hilbert-huang transform (HHT), and implementation process of EMD is analyzed. Then data compression denoising algorithm based on EMD is proposed, simulation and experimental signals are used for verification of the effect of EMD. In the same data sources, the comparison of data compression denoising approaches based on the EMD, db2 wavelet and db8 wavelet are conducted. In addition, physical experiment of the same analysis and comparisons are conducted on a running motor in a Chongqing electrical plant. Simulation and experimental results show that data compression denoising algorithm based on EMD can achieve the same denoising effect, or even better than based on db2 wavelet, db8 wavelet. The former is more perfect than the latter in the real signal processing, and denoising based on EMD is not loss of the original signal energy.     

番茄病害胁迫声发射信号采集与声源定位

以番茄为研究对象,利用声发射检测系统对番茄植株的声发射信号进行连续采集,利用上位机软件对采集到的数据进行处理和分析。对番茄的晚疫病病害胁迫声发射信号随病害程度变化进行了统计分析,得出染病植株的声发射现象并不像健康植株那样按照一定的生理周期规律发生,在染病早期作物声发射信号的频次大大增加并且随着病害严重程度而逐渐降低,并出现多峰现象。利用声发射信号到达两路传感器的时差和采集到的两路声发射信号频谱分布变化可以进行声发射源定位判断。     

半干旱农田地区DPM模型适用性初步研究

DPM模型是根据粉尘释放通量与粉尘跃移通量及跃移颗粒的动能通量成正比的原理,由土壤微团粒跃移模块以及粉尘粒子释放模块构成的。为验证DPM模型在半干旱地区农田的适用性,选取了半干旱地区陕西中北部4种典型土壤类型农田进行野外观测研究,计算分析了各观测区的地表空气动力学粗糙度、表土微团粒粒度、摩阻风速和起动摩阻风速,对比分析了不同土壤类型、不同季节DPM模型模拟的准确性。结果表明,DPM模型可以用于模拟预测我国半干旱区农田不同土壤类型粉尘释放通量,可以较好地用于模拟预测半干旱农田夏冬两季节的粉尘释放通量。     

Influence of water table level and soil properties on emissions of greenhouse gases from cultivated peat soil

A lysimeter method using undisturbed soil columns was used to investigate the effect of water table depth and soil properties on soil organic matter decomposition and greenhouse gas (GHG) emissions from cultivated peat soils. The study was carried out using cultivated organic soils from two locations in Sweden: Örke, a typical cultivated fen peat with low pH and high organic matter content and Majnegården, a more uncommon fen peat type with high pH and low organic matter content. Even though carbon and nitrogen contents differ greatly between the sites, carbon and nitrogen density are quite similar. A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil monoliths (50 cm high, Ø29.5 cm) per site. They were sown with ryegrass (Lolium perenne) after the original vegetation was removed. The lysimeter design allowed the introduction of water at depth so as to maintain a constant water table at either 40 cm or 80 cm below the soil surface. CO₂, CH₄ and N₂O emissions from the lysimeters were measured weekly and complemented with incubation experiments with small undisturbed soil cores subjected to different tensions (5, 40, 80 and 600 cm water column). CO₂ emissions were greater from the treatment with the high water table level (40 cm) compared with the low level (80 cm). N₂O emissions peaked in springtime and CH₄ emissions were very low or negative. Estimated GHG emissions during one year were between 2.70 and 3.55 kg CO₂ equivalents m⁻². The results from the incubation experiment were in agreement with emissions results from the lysimeter experiments. We attribute the observed differences in GHG emissions between the soils to the contrasting dry matter liability and soil physical properties. The properties of the different soil layers will determine the effect of water table regulation. Lowering the water table without exposing new layers with easily decomposable material would have a limited effect on emission rates.