陇东雨养苹果覆膜对土壤团聚体结构稳定性与细根分布的影响

不同的果园管理方式可影响果树根系生长、分布与土壤团聚体稳定性、有机碳固存,进而改变“根-土”复合体响应关系。对西北陇东旱塬不同覆膜年限(2 a、4 a和6 a)苹果园表层土壤(0—20 cm)细根生长进行调查,并采用干筛法和湿筛法相结合的方式对土壤团聚体进行分级(>2 mm, 0.5—2 mm, 0.25—0.5 mm和<0.25 mm)。计算团聚体稳定性参数[> 0.25 mm机械稳定性团聚体含量(DR_0.25)、> 0.25 mm水稳性团聚体含量(WR_0.25)、平均重量直径(MWD)、平均几何直径(GMD)、团聚体破坏率(PAD)、水稳系数(WSC)]和团聚体有机碳含量。分析细根生长与土壤物理结构对长期覆膜的响应,探明土壤团聚体稳定性与有机碳固持关系,揭示黄绵土物理结构稳定机制。结果表明：6 a处理通过增加表层土壤黏粒和物理性黏粒比例,改变孔隙结构,抑制细根生长,其根量、根长和根表面积仅为对照(CK)的20.97%、24.66%和41.25%;降低表层土壤团聚体力稳性,其DR_0.25、机械稳...     

Development of procedures for direct extraction of Cryptosporidium DNA from water concentrates and for relief of PCR inhibitors

Extraction of high-quality DNA is a key step in PCR detection of Cryptosporidium and other pathogens in environmental samples. Currently, Cryptosporidium oocysts in water samples have to be purified from water concentrates before DNA is extracted. This study compared the effectiveness of six DNA extraction methods (DNA extraction with the QIAamp DNA minikit after oocyst purification with immunomagnetic separation and direct DNA extraction methods using the FastDNA SPIN kit for soil, QIAamp DNA stool minikit, UltraClean soil kit, or QIAamp DNA minikit and the traditional phenol-chloroform technique) for the detection of Cryptosporidium with oocyst-seeded samples, DNA-spiked samples, and field water samples. The study also evaluated the effects of different PCR facilitators (nonacetylated bovine serum albumin, the T4 gene 32 protein, and polyvinylpyrrolidone) and treatments (the use of GeneReleaser or ultrafiltration) for the relief from or removal of inhibitors of PCR amplification. The results of seeding and spiking studies showed that PCR inhibitors were presented in all DNA solutions extracted by the six methods. However, the effect of PCR inhibitors could be relieved significantly by the addition of 400 ng of bovine serum albumin/mul or 25 ng of T4 gene 32 protein/mul to the PCR mixture. With the inclusion of bovine serum albumin in the PCR mixture, DNA extracted with the FastDNA SPIN kit for soil without oocyst isolation resulted in PCR performance similar to that produced by the QIAamp DNA minikit after oocysts were purified by immunomagnetic separation.     

Quantitative estimation of the viability of Toxoplasma gondii oocysts in soil

Toxoplasma gondii oocysts spread in the environment are an important source of toxoplasmosis for humans and animal species. Although the life expectancy of oocysts has been studied through the infectivity of inoculated soil samples, the survival dynamics of oocysts in the environment are poorly documented. The aim of this study was to quantify oocyst viability in soil over time under two rain conditions. Oocysts were placed in 54 sentinel chambers containing soil and 18 sealed water tubes, all settled in two containers filled with soil. Containers were watered to simulate rain levels of arid and wet climates and kept at stable temperature for 21.5 months. At nine sampling dates during this period, we sampled six chambers and two water tubes. Three methods were used to measure oocyst viability: microscopic counting, quantitative PCR (qPCR), and mouse inoculation. In parallel, oocysts were kept refrigerated during the same period to analyze their detectability over time. Microscopic counting, qPCR, and mouse inoculation all showed decreasing values over time and highly significant differences between the decreases under dry and damp conditions. The proportion of oocysts surviving after 100 days was estimated to be 7.4% (95% confidence interval [95% CI] = 5.1, 10.8) under dry conditions and 43.7% (5% CI = 35.6, 53.5) under damp conditions. The detectability of oocysts by qPCR over time decreased by 0.5 cycle threshold per 100 days. Finally, a strong correlation between qPCR results and the dose infecting 50% of mice was found; thus, qPCR results may be used as an estimate of the infectivity of soil samples.     

三峡山地不同类型植被和坡位对土壤水文功能的影响

土壤层下渗和贮蓄水分的水文功能是森林保持水土、涵养水源的基础。以三峡山地大老岭林区为研究区,采集常绿林、落叶林和草地覆盖下不同坡位的原状土样,测定其饱和导水率和水分特征曲线,分析植被类型和坡位对土壤水分参数和库容的影响。结果表明:常绿林地的入渗性能最好,饱和导水率为7.80—322.81 cm/d,大于落叶林地(0.33—137.03 cm/d)和草地(0.84—115.80 cm/d);坡位间差异表现为上坡高于下坡。不同样地的饱和含水量差异较小,但毛管持水量和田间持水量差异明显,草地最大,为20.77%—50.39%;不同坡位比较表现为下坡高于上坡。不同样地土壤水库容量差异较大,由田间持水量得到的库容量占总库容量的百分比以草地最大(63.25%),其次是落叶林地,常绿林地最小;坡位上表现为下坡的田间持水库容大于上坡。饱和导水率与土壤总孔隙度、有机质含量呈显著正相关,与容重呈显著负相关;饱和含水量、毛管持水量、田间持水量均与土壤总孔隙度、有机质含量和粉粒含量呈显著正相关,与容重、砂粒含量呈显著负相关。综合以上,草地持水性能最强,利于保蓄水分,常绿林地最弱,更利于水分入渗,补给地下水,下坡位的持水性能强于上坡位。     

Development of Procedures for Direct Extraction of Cryptosporidium DNA from Water Concentrates and for Relief of PCR Inhibitors

Extraction of high-quality DNA is a key step in PCR detection of Cryptosporidium and other pathogens in environmental samples. Currently, Cryptosporidium oocysts in water samples have to be purified from water concentrates before DNA is extracted. This study compared the effectiveness of six DNA extraction methods (DNA extraction with the QIAamp DNA minikit after oocyst purification with immunomagnetic separation and direct DNA extraction methods using the FastDNA SPIN kit for soil, QIAamp DNA stool minikit, UltraClean soil kit, or QIAamp DNA minikit and the traditional phenol-chloroform technique) for the detection of Cryptosporidium with oocyst-seeded samples, DNA-spiked samples, and field water samples. The study also evaluated the effects of different PCR facilitators (nonacetylated bovine serum albumin, the T4 gene 32 protein, and polyvinylpyrrolidone) and treatments (the use of GeneReleaser or ultrafiltration) for the relief from or removal of inhibitors of PCR amplification. The results of seeding and spiking studies showed that PCR inhibitors were presented in all DNA solutions extracted by the six methods. However, the effect of PCR inhibitors could be relieved significantly by the addition of 400 ng of bovine serum albumin/μl or 25 ng of T4 gene 32 protein/μl to the PCR mixture. With the inclusion of bovine serum albumin in the PCR mixture, DNA extracted with the FastDNA SPIN kit for soil without oocyst isolation resulted in PCR performance similar to that produced by the QIAamp DNA minikit after oocysts were purified by immunomagnetic separation.     

不同质地盐渍化土壤水盐含量的高光谱反演

为了方便快捷地同步监测盐渍化土壤的水、盐含量,本文以新疆典型盐渍化灌区为研究对象,基于高光谱技术、运用便携式光谱仪获取不同质地的土壤水盐含量光谱曲线,采用一阶微分、二阶微分、连续统去除的数据处理方法对土壤原始光谱进行变换.结果表明: 对原始光谱数据的变换有利于土壤属性指纹波段的提取,不同质地水盐含量的变换方法并不相同,在壤土中质量含水量为0%和10%时的水盐光谱曲线使用连续统去除方法、15%含水量使用一阶微分、19%含水量使用二阶微分,砂土中0%含水量使用连续统去除方法、10%、15%和19%含水量水盐光谱曲线使用二阶微分处理后,有利于特征波段的提取;对筛选出的变换数据采用偏最小二乘回归方法构建水盐反演模型,壤土盐度小于6.38 mS·cm^-1、砂土小于5.94 mS·cm^-1时,模型建立的建模数据集决定系数(R_cal²)、内部交叉验证(R_cv²)和外部检验数据集决定系数(R_val²)均大于0.65(P<0.05);壤土水分含量小于16%、砂土小于12%时模型反演精度较高.研究结果可为盐渍化土壤水盐含量同步监测提供阈值参考.     

A county‐level estimation of renewable surface water and groundwater availability associated with potential large‐scale bioenergy feedstock production scenarios in the United States

This study examines fresh renewable water resources available for bioenergy feedstock production in the United States. The impacts of feedstock irrigation on surface and groundwater resources available to nonbioenergy sectors were quantified using a pair of water availability indexes: streamflow availability index and percolation flow availability index. The two metrics were applied to both historical (2008) and three possible future biomass production scenarios from the 2016 U.S. Billion‐Ton Report at the county level. For both historical and future scenarios, we found that the consumptive irrigation requirements for bioenergy feedstock account for <0.01% of annual streamflow in all but three counties in Nebraska. Results suggest that the irrigation demand of future biomass production could be supplied by annual renewable groundwater flow in about 94% of feedstock‐growing counties that use groundwater for irrigation, representing about 92% of production tonnage. Counties that require irrigation from nonrenewable groundwater resources are mostly located in the Northern Plains and Pacific regions. We also evaluated the sensitivity of crop water footprint estimation to soil moisture carryover by comparing blue water estimates from six different empirical and process‐based methods. Our findings suggest that accounting for preseason soil moisture is critical for representative blue water estimation, so that the irrigation water consumption is not overestimated. This is especially true in the Corn Belt region, where blue water estimates with and without preseason soil moisture would be about 1.9 versus 45.5 billion m³/year under the historical scenario. This difference is smaller in semiarid regions like the High Plains, but the blue water estimate can still triple if soil moisture is not considered. From the perspective of renewable surface water and groundwater resources, scaling feedstock production up in the High Plains and California will require careful planning integrated with water management strategies to improve water resource conservation.     

Effects of alternate partial root-zone irrigation on soil microorganism and maize growth

Partial root-zone irrigation creates a dynamic heterogeneous distribution of soil moisture that may affect the numbers and activities of soil microorganisms. In this study, three irrigation methods, i.e. conventional irrigation (CI), alternate partial root-zone irrigation (APRI, alternate watering on both sides of the pot) and fixed partial root-zone irrigation (FPRI, fixed watering on one side of the pot), and three watering levels, i.e. well-watered, mild and severe water deficit, were applied on pot-grown maize. Numbers of soil microorganisms, plant height, stalk diameter, leaf area and biomass accumulation were monitored over the treatment period. A quadratic parabola relationship between the number of soil microorganisms and soil water content was found, indicating the number of soil microorganisms reached a peak at the mild soil water deficit condition, possibly due to better soil aeration. The peak number of soil microorganism was obtained when soil water content was 66, 79 and 75% of field capacity for CI, FPRI and APRI, respectively. Soil microorganisms were evenly distributed in both sides of APRI and their total numbers were always higher than those under other two irrigation methods for the same soil water content. The count of soil microorganisms in the dry root zone of FPRI was reduced by a lack of water. Maximum biomass accumulation was obtained under well watered condition but severe water deficit led to a 50% reduction in the CI treatment. Such reduction was much smaller under APRI and therefore the highest water use efficiency was obtained. Our results suggest that APRI maintained the best aeration and moisture condition in the soil and enhanced the activities of soil microorganisms, which might also have benefited the plant growth.     

夏玉米叶片水分变化与光合作用和土壤水分的关系

叶片是光合作用的重要器官,其含水量的变化必将影响光合作用,但关于叶片水分变化对光合作用的影响报道较少。以华北夏玉米为研究对象,利用三叶期不同水分梯度的持续干旱模拟试验资料,分析夏玉米叶片水分变化及其与叶片净光合速率和土壤水分的关系。结果表明:夏玉米叶片净光合速率对叶片水分变化的响应显著且呈二次曲线关系,叶片含水量约为70.30%时,叶片净光合速率为零;叶片含水量与土壤相对湿度呈非直角双曲线关系,叶片最大含水量约为85.14%。研究结果可为准确描述叶片水分变化对光合作用的影响及客观辨识夏玉米干旱的发生发展及监测预警提供参考。     

Strategies for restoring the structure and function of lichen‐moss biocrust communities

Biological soil crusts (biocrusts) are crucial components of dryland ecosystems, but they are slow to recover following disturbance. Herein, we evaluated several methods for restoring lichen‐moss biocrusts that included factorial applications of moss fragments in a water‐slurry (1) with and without lichen fragments (to restore biocrust taxonomic structure), (2) with and without clay (to facilitate establishment), and (3) with and without jute ground cloth (to facilitate establishment). Three and four years after inoculation, moss and lichen cover was up to five and eight times higher on jute ground cloth than on bare ground, respectively. Lichen cover was six times higher in plots where lichen fragments were added. Clay amendments did not increase moss or lichen establishment. To understand the effects of biocrust recovery on soil properties, we measured soil inorganic nitrogen, microbial biomass carbon, and soil water availability in restoration and control plots. Restored biocrusts decreased inorganic NH₄‐N availability by 67% when compared to controls 3 years after inoculation, but did not influence the availability of inorganic NO₃‐N, soil water, or microbial biomass carbon. Our results demonstrate that adding a biocrust inoculant to jute ground cloth can expedite recovery of lichen‐moss biocrust and reestablish its influence on soil properties within a few years.     

Determination of ability of several arbor and shrub species to endure and survive extreme aridity with limited-areas methods under field conditions in Horqin Sandy Land

Using limited-areas methods, the ability of several arbor and shrub species to endure and survive extreme aridity under field conditions in Horqin Sandy Land was studied, and the lowest critical soil water content that was endurable for each of these species was determined. By limiting the horizontal distribution range of the plant roots system, the limited-areas methods could decrease the spatial heterogeneity of soil water content and improve the accuracy of the determination of soil water content. This method also had the advantage of worsening the aridity endured by the plant species, proving helpful in testing the ability of these species to endure aridity. Our results showed that Prunus sibirica L., Caragana microphylla Lam., Artemisia halodendron Turcz. ex Bess., Salix gordejevii Cheng et Skv., Ulmus pumila L., and Populus pseudo-simonii Kitag. could endure critical soil water contents of 0.82%, 0.87%, 1.61%, 1.89%, 2.04% and 2.27%, respectively. The results were useful in evaluating the ability of these species to endure aridity, and had some important implications for the rational use of these species in accelerating the revegetation of sandy desertified lands.     

Determination of ability of several arbor and shrub species to endure and survive extreme aridity with limited-areas methods under field conditions in Horqin Sandy Land

Using limited-areas methods, the ability of several arbor and shrub species to endure and survive extreme aridity under field conditions in Horqin Sandy Land was studied, and the lowest critical soil water content that was endurable for each of these species was determined. By limiting the horizontal distribution range of the plant roots system, the limited-areas methods could decrease the spatial heterogeneity of soil water content and improve the accuracy of the determination of soil water content. This method also had the advantage of worsening the aridity endured by the plant species, proving helpful in testing the ability of these species to endure aridity. Our results showed that Prunus sibirica L., Caragana microphylla Lam., Artemisia halodendron Turcz. ex Bess., Salix gordejevii Cheng et Skv., Ulmus pumila L., and Populus pseudo-simonii Kitag. could endure critical soil water contents of 0.82%, 0.87%, 1.61%, 1.89%, 2.04% and 2.27%, respectively. The results were useful in evaluating the ability of these species to endure aridity, and had some important implications for the rational use of these species in accelerating the revegetation of sandy desertified lands.     

盐城海滨湿地景观演变关键土壤生态因子与阈值研究

文章以盐城海滨湿地典型区域为案例,以2011年4月和2012年4月对海滨湿地土壤数据为基础,结合2011年ETM 遥感影像,运用灰色关联分析、线性回归模拟和地统计学方法,辨识海滨湿地景观演变的关键生态因子,并确定其生态阈值。得出基本结论如下：(1)海滨湿地土壤理化性质海陆差异明显：从米草沼泽—碱蓬沼泽—芦苇沼泽,土壤水分和盐度表现出递减的趋势;土壤有机质、营养盐总体上从米草沼泽—碱蓬沼泽—芦苇沼泽,表现出两头高中间低的特征;湿润年份土壤水分高于干旱年份,湿润年份土壤盐度低于干旱年份。(2)灰色关联分析表明:干旱年份,水分＞盐度＞铵态氮＞速效钾＞有机质＞有效磷;湿润年份为：盐度＞水分＞有效磷＞铵态氮＞速效钾＞有机质,因此把土壤水分和盐度确定为海滨湿地景观演变的关键生态因子。(3)土壤水分和盐度在东西海陆方向上的变异大于南北海岸延伸方向上的变异。(4)将景观类型图和海滨湿地土壤水分与盐度分异图叠加分析,得出：芦苇滩土壤水分阈值＜42.332%,盐度阈值＜0.745%;碱蓬滩土壤水分阈值为38.836%～46.593%,盐度阈值为0.403%～1.314%;米草滩土壤水分阈值＞39.475%,盐度阈值＞0.403%;光滩的土壤阈值＞41.550%,盐度阈值＞0.656%。     

宁南山区紫花苜蓿(Medicago sativa)土壤干层水分动态及草粮轮作恢复效应

以各类作物农田水分为对照,连续两年对宁南山区不同生长年限苜蓿深层土壤水分以及10年生苜蓿地耕翻后轮作不同年份作物农田的水分进行了测定.结果表明,随着苜蓿生长年限的增加,干层深度与厚度先增加后减小.3年生苜蓿干层深度为720cm,6年生干层最深可达1000cm以下,10年生干层深度为920cm,3～12年生苜蓿地0～700cm土层基本上均属于土壤干层范围.苜蓿地0～800cm土壤湿度随生长年限增加而降低,2004年测定的4、7年生和12年生苜蓿地0～700cm土层平均含水率分别为5.30%、5.22%和5.01%;2005年测定的3、6年生和10年生苜蓿地0～800cm土层湿度分别为6.26%、5.60%和5.27%;而800～1000cm土层湿度在一定年限后有恢复趋势.300cm为苜蓿地降水下渗的最大临界深度,300cm以下土壤干层一旦形成,将长期存在,7～12年生苜蓿300～700cm土层湿度仅维持在4.0%左右.苜蓿地和农田的土壤干层厚度与湿度有较大差异,草粮轮作可使苜蓿土壤干层水分基本恢复到农田湿度,而且轮作年份越长,土壤各层次水分恢复效果越好,10年生苜蓿轮作18年后土壤水分基本恢复到农田状态.     

保护性耕作对陇中旱作农田水分特征的影响

陇中旱农区生产力水平低而不稳,而保护性耕作措施是农业可持续发展的重要途径.本研究依托2001年建立在陇中旱农区的长期不同耕作措施的定位试验,研究了不同耕作措施对土壤水分入渗、蒸发、作物产量和水分利用效率的影响.该试验共设6个处理,分别为传统耕作(T)、免耕秸秆覆盖(NTS)、免耕(NT)、传统耕作+秸秆翻入(TS)、传统耕作+覆膜(TP)、免耕覆膜(NTP),春小麦和豌豆年间轮作.结果表明:与T处理相比, NTS处理的小麦地和豌豆地的土壤容重显著降低,总孔隙度显著增加.保护性耕作措施降低了豌豆地0～5 cm土壤渗吸率,NTS处理渗吸率比T处理降低56.2%.保护性耕作提高了土壤饱和导水率,无论小麦地和豌豆地,NTS均比T处理显著提高了饱和导水率,增幅为52.8%～107.1%.保护性耕作显著降低了作物生育期棵间蒸发量,NTP、TP、NTS比T处理降低了14.4%～50.8%,并减弱了雨后土壤蒸发.保护性耕作提高了作物产量和水分利用效率,NTS、TP、NTP的产量比传统耕作提高了9.5%～62.8%,水分利用效率比传统耕作提高了0.4%～50.9%.因此,在陇中旱农区,保护性耕作措施可以提高水分利用效率,增加作物产量.     

不同耕作方式对茶园土壤物理性状及茶叶产量的影响

研究了免耕、旋耕和深松3种耕作方式对茶园土壤紧实度、土壤含水率、土壤容重、茶叶产量构成因素及茶叶产量的影响.结果表明: 3种耕作方式对土壤容重和土壤紧实度的影响效果为深松>旋耕>免耕.旋耕和深松能够打破粘盘层,降低深层土壤紧实度.0～30 cm耕层深松土壤容重较免耕下降16.4%,土壤紧实度下降13.4%～27.5%;深松可以显著增加土壤的储水空间,进而增强土壤持水能力,扩大土壤水库容,深松15～30 cm层含水量与免耕相比增加7.7%.不同耕作方式对土壤孔隙度影响不大.旋耕和深松方式下土壤比表面积增加,土壤气体和液体的比例均明显升高.茶叶的光合速率和蒸腾速率的日变化曲线均为“双峰”型,气孔因素是导致“午休”的主要原因.在深松方式下,茶树叶片蒸腾速率降低,芽叶密度增加,百芽干质量和水分利用效率升高,茶叶产量分别比免耕和旋耕增加17.6%和6.8%.深松是皖东地区茶园较为适宜的耕作方式.     

关中平原田间土壤含水量的空间变异性

为了明确田块尺度土壤含水量的空间变异特征,制定合理准确的土壤采样方法,支持田间精准灌溉,分7个日期对陕西省杨凌区曹新庄试验区土壤样品进行采集,利用经典统计学和地统计学方法,分析了0～60 cm不同土层土壤含水量的空间变异特点。结果表明: 田块尺度土壤含水量空间分布呈弱变异或中等偏弱变异;土壤含水量在11.7%～20.1%时,其值越低,空间变异性越强。采样间距显著影响土壤含水量空间变异性的计算精度,采样间距设置为东西方向间距27 m和南北方向间距9 m时的土壤含水量变异系数比采样间距设置为东西方向间距9 m和南北方向间距18 m大3.3%。随着采样密度的增大,土壤含水量分布的等值线变化增大;表征田块尺度土壤含水量空间变异性最少的网格数量为21个点。采样间距为东西方向间距18 m和南北方向间距9 m时,田块尺度土壤含水量具有较高的空间相关性,田块中间位置的土壤含水量比四周高3%～5%。本研究可为关中平原田间测定土壤含水量确定合理的采样方法,并为实现农业精准灌溉提供参考。     

Effect of soil strength on root growth under different water conditions

The objective of this study was to determine the effects of soil water and soil strength on root growth in situations where the individual effects of both of these factors were important. Three grain legumes were grown from pre-germinated seeds for five days on 50-mm compacted columns of two major soils of Sri Lanka. Four or five levels of bulk density (1.1 to 1.8 Mg.m^–3) and five or six levels of matric potential (–0.02 to–2.0 MPa) were used.Soil strength and matric potential effects on root growth were independently significant for most crop and soil combinations. Under high (wet) matric potential (>–0.77 MPa) soil conditions, the effect of soil water on root growth was evident only in its effect on soil strength. Bulk density had a significant effect on root growth independent of soil strength and matric potential in three cases.For all crops and soils, root penetration was 80% of the maximum or greater when the average soil strength (soil water not limiting) was 0.75 MPa or less, and when the average matric potential (soil strength not limiting) was –0.77 MPa or greater (wetter). Root penetration was 20% of the maximum or less when the soil strength was greater than 3.30 MPa (soil water not limiting), and when matric potential (soil strength not limiting) was less than –3.57 MPa. The use of pre-germinated seeds, which contained imbibed water, combined with a lack of water loss from the closed chambers containing the plants is the probable cause for the very low (–3.57 MPa) matric potential that allowed root growth at 20% of the maximum.     

咸阳地区近年苹果林地土壤含水量动态变化

利用人力钻采样法和烘干称重法, 研究了咸阳地区2002-2008年间苹果林地6 m深度范围土壤含水量的动态变化、土壤干层的等级、土壤干层水分恢复、动力机制与消耗过程。资料表明, 咸阳地区干旱年苹果林地土壤含水量较低, 发育了长期性土壤干层。2003和2007丰水年苹果林地土壤干层中的水分得到了显著恢复, 经过当年的水分补给, 土壤干层已经消失。丰水年土层中重力水含量较高, 并能到达2 m深度以下。持续时间较长的重力水的存在是土壤干层水分恢复的驱动力, 但干层水分恢复的直接动力是薄膜水的水膜压力。在年降水量800 mm或更多的条件下, 不论黄土厚度有多大, 土层水分完全能够满足人工林生长的需要。咸阳地区干旱年苹果林地土壤水分不足, 土壤水分收入量小于支出量, 土壤水分为负平衡, 没有剩余的水分通过入渗补给地下水;丰水年苹果林地土壤水分充足, 土壤水分收入量大于支出量, 土壤水分为正平衡, 有剩余的水分通过入渗补给地下水。在年降水量为800 mm左右的丰水年, 该区补给的土壤水分可维持苹果林地在3 a内不会出现长期性干层, 3 a之后一般还会出现长期性土壤干层。     

Soil Water Retention on Gold Mine Surfaces in the Mojave Desert

An experimental analysis of soil water retention was conducted on three substrates (an abandoned road, an overburden pile, and a heap leach) created by gold mining activities in the Mojave Desert in southeastern California. We mixed each substrate with straw, and the overburden pile and heap leach with growth medium, then applied surface rock mulch to half the plots in an attempt to increase soil water‐holding capacity for revegetation efforts. For each of the six treatments (controls included) we monitored soil water with time domain reflectometry following both a simulation of a rainfall event and a natural rainfall that occurred immediately following the simulation. Both the simulation and the rainfall increased soil water between 3 and 8%, depending on the substrate. Water retention patterns in the two‐week periods following each water addition were similar between the simulation and rainfall, and among all substrate types as values returned to background (pre‐water) conditions. The abandoned road substrate had higher background water content (16.5%) than the overburden pile (6%) and heap leach (5%). The road also had three times higher organic matter and five times higher soil nitrogen than the other two sites. Soil water retention was improved on the overburden pile by the addition of just surface rock mulch or of straw‐plus‐rock mulch. On the heap leach, increases were found with rock mulch only or with growth medium‐plus‐rock mulch. Rock mulches did not improve soil water retention and straw additions decreased soil water on the abandoned road. Judicious use of soil amendments can improve soil water conditions and improve revegetation efforts on disturbed lands in desert environments.