Soil Water Movement to Germinating Seeds

Water movement to germinating seeds of several range plantswas measured with a gammaray attenuation technique. Seeds wereplaced at a depth of 1.5 cm in soil at several water contentsand the soil water content of thin (3 mm) layers above and belowthe seeds was measured daily. It was found that the distancefrom which water was taken up by the seeds did not exceed 1cm and was not affected by soil water content. Germination wasfound to be dependent on seed water uptake, which was determinedby soil water content. The rate of seedling root growth wasnot affected by initial soil water content, but shoot growthwas strongly affected. Solutions of the water flow equation were applied to the caseof spheric geometry and infinite medium and to the case of linearflow and semi-infinite medium, in order to calculate water movementto a germinating seed or to a layer of seeds. Both the calculationsand the measurements showed that water uptake by a 2-mm-diameterseed from distances exceeding 1 cm was negligible.     

Movement of Endotoxin Through Soil Columns

Land treatment of wastewater is an attractive alternative to conventional sewage treatment systems and is gaining widespread acceptance. Although land application systems prevent surface water pollution and augment the available water supplies, the potential dangers to human health should be evaluated. Since sewage may contain high amounts of bacterial endotoxin, the removal of endotoxin from sewage by percolation through soil was investigated. It was found that 90 to 99% of the endotoxin was removed after travel of sewage through 100 to 250 cm of loamy sand soil. When distilled water was allowed to infiltrate into the soil to simulate rainfall, the endotoxin was mobilized and moved in a concentrated band through the soil column. On testing samples from actual land treatment sites, as much as 480 ng of endotoxin per milliliter was found in some groundwater samples. The presence of endotoxin in potable water is known to be a potential problem under some circumstances, but the importance of endotoxin in water supplies has not been fully assessed. Therefore, the design, operation, and management of land application systems should take into account the fate of endotoxin in groundwater beneath the sites.     

Soil saccharide extraction and detection

Extraction of soil saccharides involves the use of reagents effective in breaking hydrogen and covalent bonds between soil constituents and the saccharides. Of the many extractants proposed for saccharide determination, water is commonly used for extraction of water-soluble mono- and polysaccharides in soil. Analysis of these water extracts by colorimetric assays (anthrone-sulfuric acid and phenol-sulfuric acid methods) often show color development indicating that saccharides are present. However, high performance liquid chromatography (HPLC) and gas chromatography analyses have indicated that these colorimetric assays are prone to errors due to interferences from inorganic soil constituents such as Cl⁻, NO₃ ⁻ and Fe⁺³. When water extracts (25° or 80°C) are put through deionization resins to remove interferences little to no saccharides are present when assayed by the phenol-sulfuric acid analysis. The inability of water to extract saccharides from soil or microbial polymers was confirmed by HPLC analysis. The phenol-sulfuric acid assay was found to be acceptable for saccharide analysis of soil extracts only after being subjected to resin deionization for interference removal. The anthrone-sulfuric acid method is not considered acceptable for determining saccharides in soil.     

Anhydrobiotic Coiling of Nematodes in Soil

Nematodes of three genera (Acrobeloides sp., Aphelenchus avenae, and Scutellonema brachyurum) were induced to coil and enter anhydrobiosis in drying soil of two types: sandy loam and loamy sand. Coiling was studied in relationship to soil moisture characteristics. Coiling and the physiological state of anhydrobiosis occurred before the water in sandy soils reached a water potential of -15 bars. Coiling was maximum at 3-6 bars, depending on the soil type and nematode species. It appeared that induction of coiling and anhydrohiosis were determined by the physical forces exerted by the water film surrounding the nematode, which, for these three species, was 6-9 monomolecular layers of water, rather than the % moisture and relative humidity of the soil per se.     

Soil Water Stress and Photosynthesis in Cotton

An experiment was conducted in SPAR systems at Florence, S.C., to obtain a data set for use in the simulation of the effect of drying soil on photosynthetic rates in cotton. The plant water status was monitored using leaf water potential and stem diameter meaurements. Reductions were noted in apparent photosynthesis rates after only 5 days of soil drying, and as anticipated, there was uniform displacement of the diurnal cycle of leaf water potential, and corresponding decreases in transpiration and CO₂ uptake. The photosynthesis-light response curves indicated that an average two-fold reduction in photosynthesis rates occurred for solar radiation greater than 250 W/m². Stem diameter change (from a nonstress pre-sunrise value) and integrated stem stress were found to be good indicators of maximum daily plant water stress. The integrated stem stress gave a measure of the duration of the stress along with its magnitude. A simulation method for predicting leaf water potential from stem diameter measurements was used to show that the magnitude and duration of plant water stress increased uniformly during the experiment. This increase was representative of the decreased rates of photosynthesis measured. These data will be used in the simulation of cotton growth and yield.     

硬覆盖对土壤水热传输及作物生长发育影响的试验研究

河北省盐渍区农业水资源非常紧缺 ,农业节水势在必行。覆盖保摘技术是农田节水管理的重要措施之一 ,国内外对此有过不少研究报道。但多集中在地膜、秸秆、砂砾和化学喷涂等覆盖材料上 ,这些覆盖材料在使用中有种种不理想之处 ,如地膜覆盖容易造成残膜的“白色污染” ,并且使用年限短 ,降水不易入渗 ,中耕、除草、施肥困难 ,使作物抗病力差等[1 ] ;秸秆覆盖容易使秸秆中的毒素物质与作物间发生生化它感现象 ,影响作物生长[2 ] 。化学喷涂除了不利于农事作业外 ,还可能造成土壤污染。为此 ,我们在中国科学院南皮试区盐渍土上试用了一种新型覆…     

黄土丘陵半干旱区土壤水资源利用限度

以柠条为对象,采用中子水分仪对黄土丘陵半干旱区人工植被恢复过程中土壤水分与植物生长进行长期定位观测.结果表明:撂荒地播种后,随着时间推移,植物群落保持水能力增强,根系吸收利用水分的土层深度增加、土壤含水量下降.林地土壤出现干层,且干层土壤的深度和厚度逐年增加.植物对土壤水资源的利用限度为干层土壤深度等于最大补给深度时的土壤储水量.在黄土丘陵半干旱区人工柠条林地土壤水资源利用限度是0～290 cm土层的土壤储水量为249.4 mm.当人工林地土壤水资源接近或等于土壤水资源利用限度时,需要采取措施降低土壤水分消耗,或增加土壤水分补给,维持根系吸收利用水资源的相对稳定.     

Soil Water Content and Organic Carbon Availability Are Major Determinants of Soil Microbial Community Composition

Exploration of environmental factors governing soil microbial community composition is long overdue and now possible with improved methods for characterizing microbial communities. Previously, we observed that rice soil microbial communities were distinctly different from tomato soil microbial communities, despite management and seasonal variations within soil type. Potential contributing factors included types and amounts of organic inputs, organic carbon content, and timing and amounts of water inputs. Of these, both soil water content and organic carbon availability were highly correlated with observed differences in composition. We examined how organic carbon amendment (compost, vetch, or no amendment) and water additions (from air dry to flooded) affect microbial community composition. Using canonical correspondence analysis of phospholipid fatty acid data, we determined flooded, carbon-amended (+C) microcosm samples were distinctly different from other +C samples and unamended (–C) samples. Although flooding without organic carbon addition influenced composition some, organic carbon addition was necessary to substantially alter community composition. Organic carbon availability had the same general effects on microbial communities regardless of whether it was compost or vetch in origin. In addition, flooded samples, regardless of organic carbon inputs, had significantly lower ratios of fungal to bacterial biomarkers, whereas under drier conditions and increased organic carbon availability the microbial communities had higher proportions of fungal biomass. When comparing field and microcosm soil, flooded +C microcosm samples were most similar to field-collected rice soil, whereas all other treatments were more similar to field-collected tomato soil. Overall, manipulating water and carbon content selected for microbial communities similar to those observed when the same factors were manipulated at the field scale.     

Soil water partitioning contributes to species coexistence in tallgrass prairie

The majority of tallgrass prairie root biomass is located in the upper soil layers (0–25 cm), but species differences exist in reliance on soil water at varying depths. These differences have led to the hypothesis that resource partitioning belowground facilitates species co‐existence in this mesic grassland. To determine if plant water relations can be linked to soil water partitioning as a potential mechanism allowing C₃ species to persist among the more dominant C₄ grasses, we measured differences in the source of water‐use using the isotopic signature of xylem water, volumetric soil water content at 4 depths, and leaf water potentials. Data were collected for seven species representing C₄ grasses, C₃ forbs and C₃ shrubs over three growing seasons at the Konza Prairie (Kansas, USA) to encompass a range of natural climatic conditions. C₄ grasses relied on shallow soil water (5 cm) across the growing season and had midday leaf water potentials that were highly correlated with shallow soil water regardless of soil water availability at other portions of the soil profile (20, 40 and 90 cm). In contrast, C₃ species only used shallow soil water when plentiful at this depth; these species increased their dependence on soil water from greater depths as the upper soil layers dried. Structural equation models describing plant water relations were very similar for the three C₄ species, whereas a unique set of models and drivers were identified for each of the C₃ species. These results support soil water partitioning as a mechanism for species coexistence, as C₄ species in this grassland have relatively consistent dependence on water in shallow soil layers, whereas C₃ species show niche differentiation in water use strategies to avoid competition with C₄ grasses for water in shallow soil layers when this resource is limiting and leaf water stress is high.     

Isolation of Acinetobacter from Soil and Water

An enrichment culture procedure for isolating members of the genus Acinetobacter from soil and water is described. It involves the use of vigorously aerated mineral media at relative low pH, supplemented with acetate or other suitable carbon source and nitrate as nitrogen source. With this method, virtually all samples of soil and water yielded representatives of this genus. Semiquantitative comparisons of the numbers of Acinetobacter and of all bacteria capable of aerobic growth in a complex medium revealed that Acinetobacter constituted no less than 0.001% of the total heterotrophic aerobic population in soil and water and was one of the predominant organisms in some water samples.     

新垦红壤坡地土壤水分有效性研究

针对南方红壤地区降雨时空分布不均的特点,以未开垦的自然植被为对照,对桂西北环境移民示范区不同季节(早季和雨季)一次性降雨前1d及降雨后4h、2d、4d、6d及8d新垦蔗地(中坡、下坡、谷地）0-20cm,20-40cm、40-60cm3个土层的土壤水分含量进行了测定．结果表明,雨后谷地蔗地的土壤有效水分增量几乎与降雨量相同,而中坡蔗地与未开垦的自然植被土壤有效水分增量仅相当于降雨量于80％．雨季雨后0-60cm土壤层次中土壤有效水分分布均匀,早季主要集中在表层．雨季一次性降雨后各哩理及各土层土壤有效水分饱和度均有显著差异;而早季3个新垦蔗地间无明显差异,3个土层以表层土壤有效水分饱和度最高,亚表层与心土层差异不明显．无论雨季还是旱季,0-60cm土层土壤有效水分的消耗速率都以自然植被处理为最低,由于雨季正是作物生长旺季,其0-60cm土层土壤有效水分的消耗速率比旱季快,按照早季雨后8d土壤有效水分的平均消耗速率,15d内0-60cm土层的有效水分将消耗殆尽。     

表层岩溶动力系统中土壤水分及其岩溶效应

对广西弄拉表层岩溶动力系统中森林和灌丛的土壤容重、非毛管孔隙度等物理性质以及土壤CO₂、土壤水和泉水水化学特征进行了研究.结果表明：森林和灌丛环境下的土壤物理性质存在显著性差异,影响土壤含水量.土壤水固定CO₂浓度和土壤CO₂之间存在显著的负相关关系.森林土壤水中游离CO₂浓度为0,灌丛为5.33×10³ mg·m^-3.土壤水和泉水中pH、Ca^2＋、Mg²⁺ 、Cl^-浓度存在一定的负相关关系,其K⁺、Na^＋、HCO₃^-浓度和有机碳含量存在正相关关系.经过雨水的淋溶,土壤层各离子浓度均大幅度增加,其溶蚀能力大大增强.森林环境下的岩溶作用稳定但强度大,灌丛环境下的岩溶作用活跃但强度小.     

Desorption of Nitroaromatic Compounds From Explosive-contaminated Soil by Washing

The soil contaminated by explosive production wastewater was treated by washing using water as solvent. The effect of contact time and temperature, water/soil ratio and washing steps on desorption efficiency was investigated. Six kinetic models—parabolic diffusion model, zero-order equation, pseudo-first-order equation, pseudo-second-order equation, power function equation and Elovich equation—were used to study the desorption kinetics of nitroaromatic compounds from contaminated soil to water. The eluent of contaminated soil before and after washing was characterized by UV–vis analysis. The results showed that the removal rate was fast at the initial stage and then slowed down after 60 min. The desorption of contaminants from soil to water is endothermic. Washing with small quantities of water in high frequency is preferred when water volume is limited. The pseudo-second-order model can be used to describe the desorption process. Soil washing can remove most of the contaminants from the contaminated soil.     

Availability of Fenamiphos and its Metabolites to Soil Water

Field and greenhouse experiments were conducted to determine the extent to which fenamiphos and its degradation products, fenamiphos sulfoxide and fenamiphos sulfone, are available to contact nematodes in the soil. Water extraction provided a relative measure of each chemical''s availability to the soil water where the chemicals could contact nematodes, and methanol extraction provided a relative measure of the total amount of each chemical present in the soil. Only small amounts of fenamiphos and fenamiphos sulfone could be extracted by water, even when much larger amounts were present in the soil. In contrast, virtually all of the fenamiphos sulfoxide present in the soil was extractable by water several days after nematicide application. Three days after fenamiphos (3EC) was applied at 6.7 kg a.i./ha to field plots, 6.4% of the fenamiphos, 14.4% of the fenamiphos sulfone, and 100% of the fenamiphos sulfoxide present in the soil was extracted by water. In greenhouse experiments with soil from these field plots, a 15G formulation of fenamiphos containing 98.7% fenamiphos and 1.3% fenamiphos sulfoxide was added to the soil. After an initial period of 3-4 days, the sulfoxide which formed by oxidation of fenamiphos became completely available for water extraction, whereas fenamiphos remained relatively unextractable by water. Fenamiphos sulfoxide is much more available to soil water, thus available for contact with nematodes, than are fenamiphos or fenamiphos sulfone. Based on this availability in water, it seems likely that fenamiphos sulfoxide is the major component for controlling nematodes.     

覆膜开孔土壤蒸发实验研究

为获得灌后覆膜开孔蒸发过程中土壤含水率分布的动态资料,研制了室内垂直一维入渗-覆膜开孔蒸发动态观测实验系统,并进行了不同覆膜开孔率和不同入渗定额下的覆膜开孔蒸发实验.根据实测资料分析了土表覆膜开孔率和入渗定额不同条件下,蒸发土壤含水率剖面的时间变化和蒸发结束的含水率剖面特征.累积蒸发量随时间变化趋势表明,两者关系符合Gardner理论关系,且该理论关系系数与不同覆膜开孔率和入渗定额存在进一步的函数关系,从而得出覆膜开孔率和入渗定额影响下的累积蒸发量随时间变化多因子模型.同时,采用类似的方法分析了覆膜开孔率和入渗定额对相对累积蒸发量和单位膜孔面积累积蒸发量的影响,得出了定量函数关系,其拟合的相关系数均很高.     

Soil water regime of agricultural field and forest ecosystems

The unsaturated zone of soil is one of the most important and complicated parts considering the water movement in the hydrologic cycle. Water transfer through its upper and lower boundary directly influences the amount of water in this zone. The depth of groundwater table usually delimits the lower boundary. The soil surface with or without plant canopy is the upper boundary. The soil surface reacts directly on meteorological conditions primary through evapotranspiration. It is determining the inflow of precipitation into deeper layers of a soil profile. Both physical and hydrophysical properties of the upper soil layer are changed under the extreme meteorological conditions. In case of such conditions the water can flow along preferential pathways down to the groundwater without filling up the soil matrix. Changes of physical and hydrophysical characteristics of the soil surface layer or of the root zone depend on the vegetation type, too. The water storage of 0–30 cm and 30–60 cm soil layers was calculated from monitored data of soil water contents in two different ecosystems, and the calculated water storages were compared with the integral water contents that are related to hydrolimits (field capacity, point of decreased availability and wilting point) in 1999 and 2000. It should be noted that it was considerably dryer in 2000 than in 1999, and during the vegetation period, it was also warmer in 2000 than in 1999. The higher air temperatures during the vegetation season and the lower cumulative rainfall in 2000 comparing to 1999 resulted in a decrease in the integral water contents in the root zone.     

Soil water dynamics and vegetation patterns in a semiarid grassland

Long-term (1985–1992) dynamics and spatial variations in soil water below the evaporative zone were evaluated for a shortgrass steppe with a low and variable precipitation regime. Each of a sandy loam, clay loam, and two sandy clay loam sites comprised a toposequence with upland, midslope and lowland positions. Soil water was monitored at 15 cm intervals providing estimates covering 22.5 to 97.5 cm depths.Soil water throughout the profile was highest in the clay loam site and lowest in the sandy loam site. However, stored soil water did not vary systematically among slope positions. Total vegetation cover was highest on the lowland in two sites, but was greatest on the midslope position in the other two. Total vegetation cover was greatest on the CL site, which was the wettest in terms of soil water. Soil water depletion was related to the depth-distribution of roots. There was an inverse relationship between aboveground production and soil water content of the 30, 45 and 60 cm layers during the growth period. Root distributions through the profile did not, however, vary with soil texture or with different soil water profiles controlled by texture. The less variable water content of deeper soil layers is a resource which potentially buffers the impact of pronounced variability in precipitation and thus contributes to vegetation stability of the shortgrass community.     

Occurrence of Inverted Water Potential Gradients between Soil and Bean Roots

Measurements with a pressure chamber were made of the xylem water potential of leaves, shoots and roots from bean plants (Pkaseolus vulgaris L. cv. Processor) grown with a 12 hour dark period and natural or artificial light conditions during the day. The water potentials were measured at the end of a dark period and during the light period. Measurements taken at the end of the dark period indicated normal potential gradients within the soil/plant system (leaf < shoot < root < soil), when the matric potential of soil water was relatively high (above ?0.02 bar), and the gradients then also remained normal during the day (natural light). When the soil water potential was ?1 bar or lower in the morning, however, the root xylem water potential was higher than the soil water potential; at very low soil water potentials (< ?4 bar) it remained higher during most of the day. In this case also leaf and shoot xylem water potentials were higher than the soil water potential in the early morning, although decreasing rapidly in daylight. Under artificial light, both leaf and root water potentials were higher than the soil water potential throughout the whole diurnal cycle when the latter potential was below ?4 bar. From measurements of stomatal diffusion resistance, transpiration, relative water content of leaves and of changes in the matric potential of soil water, it was concluded that when the matric potential of soil water was low, water could be taken up by the plant against a water potential gradient. Because leaf xylem water potential was always lower than root xylem water potential, the mechanism involved in the inversion of water potential gradient must be localized in the roots, and probably related to ion uptake. Symbols and abbreviations used in the text: Ψ: Plant water potential (thermocouple psychrometer); Ψx: Xylem water potential (pressure chamber); Ψs: Osmotic potential of xylem sap; Ψm: Matric potential of soil water; RWC: Relative water content.     

Assessment of Micro-Basin Tillage as a Soil and Water Conservation Practice in the Black Soil Region of Northeast China

Micro-basin tillage is a soil and water conservation practice that requires building individual earth blocks along furrows. In this study, plot experiments were conducted to assess the efficiency of micro-basin tillage on sloping croplands between 2012 and 2013 (5°and 7°). The conceptual, optimal, block interval model was used to design micro-basins which are meant to capture the maximum amount of water per unit area. Results indicated that when compared to the up-down slope tillage, micro-basin tillage could increase soil water content and maize yield by about 45% and 17%, and reduce runoff, sediment and nutrients loads by about 63%, 96% and 86%, respectively. Meanwhile, micro-basin tillage could reduce the peak runoff rates and delay the initial runoff-yielding time. In addition, micro-basin tillage with the optimal block interval proved to be the best one among all treatments with different intervals. Compared with treatments of other block intervals, the optimal block interval treatments increased soil moisture by around 10% and reduced runoff rate by around 15%. In general, micro-basin tillage with optimal block interval represents an effective soil and water conservation practice for sloping farmland of the black soil region.     

亚热带不同树种土壤水源涵养功能

亚热带地区由于大面积的砍伐使天然林被人工林所代替,对森林土壤水源涵养功能造成了很大影响。树种可以通过自身特性来改变土壤物理结构进而影响土壤持水能力,因此合理选择树种对区域水源涵养具有重要意义。然而,立地条件的差异往往会对实验结果产生影响。为减少立地条件的差异,2012年2月在土壤发育和经营历史相同的林地上建立了中亚热带常见树种同质园。2019年8月测定了种植12个树种后不同土层(0—10、10—20、20—30、30—40 cm和40—50 cm)的土壤容重、含水量、总/毛管/非毛管孔隙度、最大/毛管/非毛管持水量和蓄水量。结果表明,种植不同树种7年后,土壤容重、含水量、总/毛管/非毛管孔隙度、最大/毛管/非毛管持水量和蓄水量均在表层(0—20 cm)土壤中差异显著,而在深层(20—50 cm)土壤中差异不显著。土壤孔隙度、持水量和蓄水量均与土壤容重呈显著负相关关系,而与土壤含水量呈显著正相关关系。与其他树种相比,种植鹅掌楸、枫香和全缘叶栾树等落叶阔叶树种可在较短时间内增加土壤孔隙度,提高土壤持水量和蓄水量。因此,在亚热带人工林经营管理中,可在杉木、马尾松纯林中适当引入鹅掌楸、枫香和全...