土壤水稳定性测试装置的设计

我国水土流失非常严重,土壤团聚体的水稳定性与水土流失有密切的关系,团聚体的水稳定性也是评价土壤物理性能的重要指标。通常采用湿筛法对土壤团聚体的水稳定性进行测定,根据湿筛法原理设计了一种用于在实验室内对土壤进行水稳定性测试的试验装置。土壤水稳定性测试装置是用来测试土壤结构在水冲刷下的抗破坏能力。该装置有以下特点:一、土壤杯的筛底可以更换不同目数的筛网。二、土壤杯上下往复运动的行程可以改变,行程范围是:0—13 mm。三、土壤杯往复运动的频率可以改变。频率范围是:每分钟25—48次。四、结构紧凑、易操作。

黄土丘陵沟壑区不同退耕模式的土壤水文性质影响对比

为系统评价黄土丘陵沟壑区在“退耕还林(草)”工程实施后不同退耕模式下的土壤水分涵养功能,选取0-200 cm土层的蓄水量、土壤含水量分层比、土壤水吸力和土壤含水量年际变化率作为土壤层水分蓄存、渗透、保持和稳定性的表征指标,分别对比了不同退耕模式下的土壤水文性质。结果表明:(1)各退耕模式下土壤蓄水量差异显著,撂荒模式的土壤蓄水量最高,为还灌和还乔模式下的1.6,1.7倍;(2)还乔模式下表层土壤水分的渗透性最优,深层土壤水分的渗透潜力最大;(3)各退耕模式的土壤持水性差异显著,还乔模式下土壤水分的保持能力突出;(4)撂荒模式土壤水分的稳定性最佳,各模式0-200 cm内土壤水分的稳定性在30年前后出现拐点,土壤含水量的年际变化率由负转正,并在120 cm以下土层较为稳定。

套作及秸秆还田对西兰花连作田土壤团聚体分布的影响

随着蔬菜的规模化与集约化发展,菜田连作障碍日趋严重,合理间套作与秸秆还田对恢复菜田土壤生态环境有很大的潜力。该文基于6a的田间长期定位试验,以西兰花单作为对照,设置西兰花套作糯玉米且糯玉米秸秆还田-西兰花(B/MR-B)、西兰花套作糯玉米且糯玉米秸秆不还田-西兰花(B/M-B)、西兰花-西兰花(B-B),共3个处理。采用湿筛法探索了套作糯玉米(Zea mays L.sinensis Kulesh)并秸秆还田对连作西兰花(Broccoli)田土壤固碳能力以及土壤水稳定性团聚体分布的影响。结果表明:随着土层的增加,不同处理的水稳定团聚体分布呈粒径逐渐减小、分布范围呈逐渐集中趋势。随着生育时期的推进,幼苗期和花球生长期水稳性团聚体多集中于0.25~0.5 mm与<0.25 mm粒径范围;营养生长期多集中于0.5~1 mm与0.25~0.5 mm粒径范围;而秋菜收获期则多分布于0.5~1 mm、0.25~0.5 mm与<0.25 mm粒径范围。B-B处理下各个时期0~40 cm土层的粒径0.5~1 mm和0.25~0.5 mm的水稳性团聚体基本呈现低于其他处理,相反B-B处理下的粒径<0.25 mm水稳性团聚体均呈现显著高于其他处理。秋季西兰花整个生育期水稳定性大团聚体均表现为B/MR-B>B/M-B>B-B。B/MR-B处理的土壤有机碳(SOC)含量显著高于其他处理。多元回归分析表明土壤水稳定性大团聚体与土壤有机碳含量在0~10 cm与10~20 cm土层中呈极显著(P<0.01)正相关,20~40 cm土层呈显著(P<0.05)正相关。综上,套作糯玉米并秸秆还田能有效提高连作西兰花田耕作层土壤水稳定性大团聚体的比例,改善连作导致的土壤理化性状的恶化。

SMOS与SMAP过境时段表层土壤水分的稳定性研究

SMOS和SMAP都是为获取全球土壤水分信息而设计的专题卫星,均搭载了L波段辐射计。进行二者的横向对比是构建具有一致性的全球土壤水分数据集的关键基础。虽然SMAP、SMOS名义上的过境时刻是固定的,但二者的实际过境时刻随时间和空间发生变化,它们与地面实测数据三者之间难以匹配形成时序上严格统一的样本对,从而给土壤水分反演结果的精度评定带来困难。针对这一问题,以美国大陆地区为研究区,首先对2016~2017年SMOS、SMAP土壤水分数据的时间戳进行统计,判定二者过境的交叠时段;进而利用高观测频率、大空间尺度的实测数据,研究表层土壤水分在此时段内的自然变化特征。结果显示,按照全部、无降水、有降水3种条件,在样本量分别为98.14%、99.51%和88.49%的绝大多数情况下,表层土壤水分的变化量为0.007 m^3/m^3、0.007 m^3/m^3和0.012 m^3/m^3,远小于SMOS、SMAP的目标精度(0.04 m^3/m^3)。初步证实:①SMOS与SMAP的土壤水分反演结果(L2数据)可进行直接比对;②过境时刻差异对验证误差的影响可不计。

含蒙脱土和多糖的保水剂对土壤物理性质的影响

以2-丙烯酰胺基-2-甲基丙磺酸、丙烯酰胺为单体,天然产物蒙脱土(MMT)和羧甲基纤维素钠(CMC)为复合组分,在室温下合成了天然组分含量大于40%的保水剂。研究了天然组分含量和聚合条件对土壤持水性、孔隙度、容重和水稳定性大团聚体的影响。正交极差分析表明,MMT对土壤持水性、孔隙度的影响最强,CMC对土壤非毛管孔隙度的影响较强。MMT的加入可以显著提高土壤的持水性、孔隙度和水稳定性团聚体总量;CMC可提高土壤的非毛管孔隙度、促进水稳定性团聚体的形成。在土壤中加入0.3%优化后的保水剂,土壤的最大持水量、田间持水量、非毛管孔隙度、毛管孔隙度、土壤水稳定性大团聚体总量及其平均粒径分别提高了41.3%、52.5%、120%、31%、90%和78%。

丛枝菌根影响植物抗旱性机理研究

随着全球变暖的日益加剧,干旱的范围以及强度也在逐渐的增强,相关研究表明,我国的干旱区域正在逐渐的扩大,干旱与半干旱区的界限也在由西北向东部移动,这种变化也必然导致生态系统的变化。近年来,人们对于丛枝菌根已经有了一定的认识,但是目前对于丛枝菌根植物适应干旱胁迫的生理和分子机制还是缺乏相应的深入研究,因此,本文将对这些做相关更深入的研究,旨在了解丛枝菌根在干旱与半干旱环境中对增强植物抗寒性的潜在作用。

Formation and Water Stability of Aggregates in Red Soils as Affected by Organic Matter

The water stability of aggregates in various size classes separated from 18 samples of red soils under different managements, and the mechanisms responsible for the formation of water-stable soil aggregates were studied. The results showed that the water stability of soil aggregates declined with increasing size, especially for the low organic matter soils. Organic matter plays a key role in the formation of water-stable soil aggregates. The larger the soil aggregate size, the greater the impact of organic matter on the water stability of soil aggregates. Removal of organic matter markedly disintegrated the large water-stable aggregates (> 2.0 mm) and increased the small ones (< 0.25-0.smm) to some extent, whereas removal of free iron(aluminium) oxides considerably destroyed aggregates of all sizes, especially the < 0.25-0.5 mm classes. The contents of organic matter in water-stable aggregates increased with aggregate sizes. It is concluded from this study that small water-stable aggregates (< 0.25-0.5 mm) were chiefly cemented by Fe and Al oxides whilst the large ones (> 2.0 mm) were mainly glued up by organic matter. Both free oxides and organic matter contribute to the formation and water stability of aggregates in red soils.

Role of Organic Matter in Formation and Stability of Aggregates in Mulberry Plantation Soils

The role of organic matter in the formation and stability of soil aggregates in mulberry plantation in the Hang-Jia-Hu Plain, northern Zhejiang Province, was evaluated in this study. A positive correlation was found between water-stable aggregate contents and organic matter contents in the mulberry plantation soils, which supported the hypothesis that organic matter was the main cementing agent in formation of aggregates. A close correlation was also found between stability of aggregate and organic matter contents. Regression analysis showed that total nitrogen content was also an indicator of water-stable aggregate content and stability. The aggregate size distribution indicated that the water-stable aggregates 1--0.25 mm in diameter were the major component of the aggregates in the mulberry plantation soils. The organic matter contents of aggregates ranging from 5 to 0.25 mm in diameter increased with the decrease of aggregate sizes, and the aggregates 1-0.25 mm in diameter had the maximum organic matter content.

Light Fraction Carbon and Water-Stable Aggregates in Black Soils

The distribution of light fraction carbon （LF-C） in the various size classes of aggregates and its relationship to water- stable aggregates as well as the influence of cultivation on the organic components in virgin and cultivated black soils were studied by wet sieving and density separation methods. The total organic carbon （TOC） and LF-C were significantly higher （P≤ 0.05） in the virgin soils than in the cultivated soils. The LF-C in aggregates of different size classes varied from 0.9 to 2.5 g kg^-1 in the cultivated soils and from 2.5 to 7.1 g kg^-1 in the virgin soils, whereas the ratio of LF-C to TOC varied from 1.9% to 7.3% and from 5.0% to 12.2%, respectively. After being incubated under constant temperature and controlled humidity for three months, the contribution of LF-C to TOC sharply decreased to an amount （1.7%4.5%） close to the level in soils that had been cultivated for 20 to 25 years （1.3%-8.8%）. As a result, the larger water-stable macro-aggregates （especially 〉 1 mm） decreased sharply, indicating that the LF-C pool in virgin soils declined quickly after cultivation, which reduced the water stability of soil aggregates.

Slide stability of hydraulic structures on subbed soil

The study on slide stability of hydraulic structures on subbed soil was made. Using the slide test results of dragged concreting base plates on subbed soil pits, the decreased value of bearing capacity on slide after re- bound and repression influence of subbed soil was determined, and the envelope of ultimate slide shear resistance was also quantitatively determined. Due to the lack of similar mechanisms of slide stability on subbed soil and base plate of hydraulic structures, different safety coefficients for the slide stability were adopted. It was suggested to use the maximum compressive stress O＇m~ of eccentric load to predict structure displacement, slide and creepy slippage of subbed soil, to determine the sliding creepy contour and limit the maximum load on subbed soil. Two hydraulic structures that had been put into operation were reviewed by this method, and the results accorded with the real conditions.

Effect of Freeze-Thaw on Water Stability of Aggregates in a Black Soil of Northeast China

Soil aggregate stability,an important index of the physical characteristics of a soil,can provide a good indication of a soil’s erodibility,and deserves special consideration in regions with cold climate.The objective of this study was to study the effect of freeze-thaw on soil water-stable aggregates in the black soil region of Northeast China.Samples of a typical black soil in the region were collected to measure water-stable aggregates after freeze-thaw under different conditions(i.e.,initial moisture contents,freezethaw cycles and freezing temperatures)by wet-sieving into eight particle size groups(>10,10–6,6–5,5–3,3–2,2–1,1–0.5,and0.5–0.25 mm).Freeze-thaw had the most effect on aggregate stability when the samples had an initial moisture content of 400 g kg-1.The water-stable aggregates of the four larger particle size groups(>5,5–3,3–2,and 2–1 mm)reached a peak stability value,but those of the two smaller particle size groups(1–0.5 and 0.5–0.25 mm)reached a minimum value when the soil moisture content was 400 g kg-1.Water-stable aggregates of the four larger particle size groups decreased while those of the two smaller particle size groups increased with the increase of freeze-thaw cycles.As temperatures fell,the water-stable aggregates of the four larger particle size groups decreased while those of the two smaller particle size groups increased.

Performance of ground penetrating radar in root detection and its application in root diameter estimation under controlled conditions

A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root sys- tems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excava- tion/drilling location is of prime importance. Ground penetrating radar （GPR） provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the perfor- mance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled envi- ronment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radar- grams were subject to the influence of the following factors： size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T2 （p〈0.001, t=0.795）. Because GPR root detection is highly site-specific, this study provides a local refer- ence for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.