Micro-Spatial Variability of Soil Nitrate Following Nitrogen Fertilization and Drip Irrigation

Micro-spatial analysis of nitrate (NO₃), an environmental contaminant partially attributed to nitrogen fertilization, can be useful for estimating its distribution in soils. A study was conducted to determine the micro-spatial distribution of soil NO₃ using kriging and cokriging in a drip-irrigated and nitrogen-fertilized field. One hundred soil samples were collected in a regular grid pattern from a 10 m × 20 m plot, and analyzed for soil NO₃ and pH. The effect of reduced sample size on NO₃ estimation was also evaluated. The pH data indicated the soils were slightly acidic to neutral with log[NO₃] values ranging from 1.66 to 2.95. These parameters were inversely related; which was probably an attribute of soil nitrification process. Sample variograms and cross-variograms suggested that the spatial distribution of pH and log[NO₃] could be described by linear models in the area studied, as indicated by small MSE (mean sum error), and RKV (reduced kriging variance) values close to 1. Contour maps based on kriging and cokriging estimates indicated greater homogeneity of the variables in the south-north direction than the east-west, except for zones of high NO₃ and low pH in the north-central edge and north-east corner of the grid area. Cokriging of log[NO₃] estimation, using pH data, improved MSE, MSSE (mean sum square error), MKV (mean kriging variance), RKV, CEE (correlation between estimated data and error), CEM (correlation between estimated and measured data) by 46, 31, 30, 22, 96, and 98%, respectively, as compared to kriging. Lower cokriging variance for any estimated log[NO₃] value, as compared to the kriging analysis, indicated that cokriging provided more accurate estimates. With reduced sample observations (n) for NO₃ similar conclusions were obtained; and the estimation accuracy was maintained up to n >70. Cokriging analysis with reduced n also curtailed the analytical cost, and facilitated NO₃ estimation by means of pH, which was measured at a cheaper cost.     

灌水效率碘—淀粉显色示踪试验

该文旨在研究不同土质、灌水量和灌水方法情况下入渗模式、灌水效率,并探讨不同灌水条件下溶质分布和水流运动模式之间的关系。根据碘－淀粉显色原理示踪水流运动和溶质迁移,分别在壤土和黏土条件下、开展了重力灌溉和微灌方式下的12组入渗试验,采用适用效率、深层渗漏损失率、有效储水率和均匀度对灌水效率进行综合评价。结果表明,入渗水再分布主要受到湿润模式的影响,有效储水率和均匀度随着灌水量的增加而提高,然而深层渗漏损失率也明显增大。溶质分布的均匀程度和深层渗漏损失率均小于水量分布的均匀程度和损失率,根据入渗后水分和溶质的再分布情况对灌水效率进行评价更为直接和全面。     

流域面源污染负荷差异性及不确定性的尺度特性分析

针对流域面源污染负荷差异性及其不确定性的尺度特性问题,于2013-2015年在釜溪河流域测定了不同尺度汇流区的面源污染负荷和污染物转化动力学参数。分别采用动态时间弯曲距离DTW(dynamic time warping distance)和信息测度度量了不同尺度汇流区面源污染的负荷差异性和不确定性。结果表明:不同的汇流区尺度上,降雨量小于临界值(40 mm)的情况下,氨氮(NH_3)、总氮(TN)、总磷(TP),和高锰酸盐指数(I_(Mn))负荷均随降雨量的增加而非线性增大,降雨量超过临界值后,流域面源污染出现最大负荷。降雨量超过临界值后,由于尺度增加后下垫面对径流过程调蓄能力的增大,相比子流域尺度,流域尺度上NH3、TN、TP和I_(Mn)负荷的变异系数分别增加了69.1%、47.0%、14.2%和85.8%。枯水期和汛期面源污染负荷主要受到污染源流域分布特性和下垫面径流条件的影响,不同尺度汇流区的NH3、TN、TP和I_(Mn)负荷在枯水期的差异性均显著小于汛期的差异性,子流域之间、以及子流域与流域之间4种污染负荷的差异性平均增大了3.18倍和2.44倍。相比子流域尺度,在流域尺度上单位面积流量、TN、TP和I_(Mn)负荷基质熵分别减小了4.8%、9.3%、31.9%和10.7%,而NH3增加了15.3%;有效测定复杂度分别增加了4.6%、15.4%、17.4%、49.5%和19.8%。不同尺度汇流区的面源污染负荷过程与流量过程不具有完全同步性。随着汇流区尺度的增大,面源污染负荷不确定性减小;有效测量复杂度随尺度增大表明在更大的尺度上对于面源污染负荷有效预测的参数数量显著增加;涨落复杂度和平均信息增量关系表明随着尺度的增加,面源污染负荷对降雨量的敏感性降低,而对下垫面条件的敏感性增加。不同尺度条件下,面源污染对降雨和下垫面的敏感性变化规律、以及面源污染负荷变异性机理等方面的研究将有助于提升分布式水文及面源污染模型理论。     

Interactions of Denitrifying Bacteria, Actinomycetes, and Fungi on Nitrate Removal in Mix-Culturing Systems

Bacteria, actinomycetes, and fungi are the dominant components of the soil microflora, and some of their species can perform denitrification. The aim of this study was to investigate the interactions of three kinds of denitrifiers in mix-culturing systems. Three denitrifying strains, i.e., one bacterial strain (strain B5), one actinomycete strain (strain A2), and one fungal strain (strain F1), were isolated from a rice paddy soil. Denitrifier interactions were examined by analyzing the population dynamics and metabolic substance in the mix-culturing systems with two and three strains and by estimating the effects of cell-free culture filtrates on the strains. Results showed that the growth of B5 was enhanced by F1 and A2, respectively, and nitrate removal proportions in the culture systems increased from 52% (B5) to 64% (B5 + F1) and 67% (B5 + A2), and the nitrate removal was further enhanced in the three strain mix-culturing system (74%, A2 + F1 + B5). Strain B5 stimulated the cell growth of A2 directly and indirectly. The existence of A2 was lethal for cell growth of F1, while A2 was also suppressed by F1. The suppressive interaction reduced nitrate removal rates from the single systems of 12.8 (F1) and 11.5?mg?L^?1?day^?1 (A2) to 8.75?mg?L^?1 day^?1 (A2 + F1). Likewise, F1 was inhibited by B5. The results also showed that the cell-free culture filtrates of other strains suppressed the cell growth of B5 and F1, respectively, but enhanced the cell growth of A2. In addition to the direct effect of cell-free culture filtrates, other indirect relationships could affect the denitrifier spatial distributions and balance of the suppression or promotion effects, which were beneficial to maintain the microbial structure and function stability with a low nitrous oxide emission in the soil.     

Nitrate reduction coupled with microbial oxidation of sulfide in river sediment

Purpose

Nitrate (NO ₃ ^? ) is often considered to be removed mainly through microbial respiratory denitrification coupled with carbon oxidation. Alternatively, NO ₃ ^? may be reduced by chemolithoautotrophic bacteria using sulfide as an electron donor. The aim of this study was to quantify the NO ₃ ^? reduction process with sulfide oxidation under different NO ₃ ^? input concentrations in river sediment.

Materials and methods

Under NO ₃ ^? input concentrations of 0.2 to 30?mM, flow-through reactors filled with river sediment from the Pearl River, China, were used to measure the processes of potential NO ₃ ^? reduction and sulfate (SO ₄ ^2? ) production. Molecular biology analyses were conducted to study the microbial mechanisms involved.

Results and discussion

Simultaneous NO₃ ^? removal and SO₄ ^2? production were observed with the different NO ₃ ^? concentrations in the sediment samples collected at different depths. Potentially, NO ₃ ^? removal reached 72 to 91?% and SO ₄ ^2? production rates ranged from 0.196 to 0.903?mM?h^?1. The potential NO ₃ ^? removal rates were linearly correlated to the NO ₃ ^? input concentrations. While the SO ₄ ^2? production process became stable, the NO ₃ ^? reduction process was still a first-order reaction within the range of NO ₃ ^? input concentrations. With low NO ₃ ^? input concentrations, the NO ₃ ^? removal was mainly through the pathway of dissimilatory NO ₃ ^? reduction to NH ₄ ⁺ , while with higher NO ₃ ^? concentrations the NO ₃ ^? removal was through the denitrification pathway.

Conclusions

While most of NO ₃ ^? in the sediment was reduced by denitrifying heterotrophs, sulfide-driven NO ₃ ^? reduction accounted for up to 26?% of the total NO ₃ ^? removal under lower NO ₃ ^? concentrations. The vertical distributions of NO ₃ ^? reduction and SO ₄ ^2? production processes were different because of the variable bacterial communities with depth.     

土壤优先流运动的活动流场模型分形特征参数计算

活动流场模型分形特征参数控制着优先流的产生和发展,因此准确获得活动流场模型分形特征参数值对提高模型的模拟预测精度具有重要意义。该研究采用染色示踪方法,将优先流流场从流动背景中显示出来,通过数字图像分析和采样分析获得优先流流场和流场内土壤含水率的分布模式,根据活动流场模型本构方程拟合活动流场模型分形特征参数值;针对3种常见的入渗后染色区内土壤含水率分布模式,分别提供了相应的活动流场模型分形特征参数的计算方法。研究结果显示,1）由于入渗后土壤水重分布的影响,活动流场区域和染色区域在整个入渗深度范围并不完全重合,因此仅可选择活动流场与染色区域相重合深度范围内受土壤初始含水率影响较小的数据来拟合活动流场模型分形特征参数值;2）土壤质地对入渗后染色区内土壤含水率的分布模式有显著影响,细质地土壤中入渗后染色区土壤含水率沿入渗方向逐渐减小,粗质地土壤中入渗后染色区土壤含水率沿入渗方向先增大后减小。     

Influence of current and previous crops on soil basal and potential denitrification rates

Soil and crop management including crop rotation influences available organic carbon and soil nitrate levels, which may in turn affect denitrification losses from soils. The objective of this paper was to determine how the current and previous crop affect denitrification by comparing the basal denitrification rate (BDR), denitrification rate with added nitrate (DAN), and potential denitrification rate (PDR) (amended with glucose and nitrate) of a clay loam soil under monoculture corn (C), soybean (S), and winter wheat (WW) with or without underseeded red clover (RC) and under each phase of a 2-year crop rotation (C-S) and two 3-year crop rotations (C-S-WW, C-S-WW+RC). The BDRs were greater in the 3-year C-S-WW rotation treatments than in the 2-year C-S rotation and monoculture C, S, and WW treatments. The WW+RC phase of the C-S-WW+RC treatment was found to have a greater BDR and DAN than the corn phase of the rotation. Available organic carbon was found to limit denitrification in the BDR and DAN incubations as evidenced by the 2- to 21-fold increase in denitrification when glucose was added in the PDR assay. Further, the significant relationship between soil respiration and BDR suggests that available carbon was a limiting factor. This study found that both the current crop and previous crops in a rotation affected soil denitrification rates substantially; and that denitrification rate was increased when a mixture of crop residues were added to soil (i.e., from growing crops in rotation) relative to when only a single residue was added (i.e., monoculture cropping).     

土壤基质吸力与土壤微生物活性关系的研究

研究了土壤微生物活性与土壤基膜吸力的关系，将土壤发泡点，即土壤导气率由0突变为非0时的基质吸力，与微生物的最高呼吸活性相联系，试图证明土壤微生物的最高活性发生于略高于土壤发泡点的基模吸力。对粗沙土、细沙土和砂壤土三种轻质地土壤的测定表明，土壤微生物的最高呼吸活性发生在略高于土壤发泡吸力的基质吸力。土壤基模吸力较小时微生物活性到达最高值的速度较慢，土壤基模吸力在发泡点附近时，微生物活性到达最高值的速度较快。     

Effects of biochars derived from different feedstocks and pyrolysis temperatures on soil physical and hydraulic properties

Purpose

Biochar addition to soils potentially affects various soil properties, and these effects are dependent on biochars derived from different feedstock materials and pyrolysis processes. The objective of this study was to investigate the effects of amendment of different biochars on soil physical and hydraulic properties.

Materials and methods

Biochars were produced with dairy manure and woodchip at temperatures of 300, 500, and 700 °C, respectively. Each biochar was mixed at 5 % (w/w) with a forest soil, and the mixture was incubated for 180 days, during which soil physical and hydraulic properties were measured.

Results and discussion

Results showed that the biochar addition significantly enhanced the formation of soil macroaggregates at the early incubation time. The biochar application significantly reduced soil bulk density, increased the amount of soil organic matter, and stimulated microbial activity at the early incubation stage. Saturated hydraulic conductivities of the soil with biochars, especially produced at high pyrolysis temperature, were higher than those without biochars on the sampling days. The treatments with woodchip biochars resulted in higher saturated hydraulic conductivities than the dairy manure biochar treatments. Biochar applications improved water retention capacity, with stronger effects by biochars produced at higher pyrolysis temperatures. At the same suction, the soil with woodchip biochars possessed higher water content than that with the dairy manure biochars.

Conclusions

Biochar addition significantly affected the soil physical and hydraulic properties. The effects were different with biochars derived from different feedstock materials and pyrolysis temperatures.     

基于两组负水头入渗数据推求Brooks-Corey模型中的参数

非饱和土壤水分运动和溶质运移的研究需要准确的土壤水动力特性信息，然而土壤水动力特性的测定往往费时费力且较难。该研究假设土壤水力动力特性可用Brooks-Corey模型来描述，结合Darcy定理和质量守恒推导了基于两组负水头下入渗数据来估计Brooks-Corey模型参数的方法。利用负水头下一维土壤水分运动中累计入渗量和湿润峰之间的关系实现了参数的求解，大量的数值模拟数据检验了该方法，并与Wang的方法进行了比较和分析，结果表明本研究提供了一种简单而且精确的确定土壤水动力参数方法。