首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 171 毫秒
1.
傅赵聪  王翀  吴春发  骆永明  刘东 《土壤》2023,55(4):829-837
以甘肃白银某污灌区重金属污染农田土壤为研究对象，对影响高精度便携式X荧光光谱（HDXRF）法总镉（CdT）测定精度的主要因素进行了筛选，分别研究了土壤水分、有机质类型与含量、土壤类型对HDXRF法CdT测定的影响，并采用相对误差（RE）、相对标准偏差（RSD）和决定系数（R2）对测定结果的准确度和精密度进行了评价。结果表明：HDXRF法CdT测定的RE≤10%、RSD≤10%、R2>0.99，符合农田土壤环境质量监测技术规范和美国环境保护署标准的准确度和精密度规定。HDXRF法CdT测定结果随着土壤水分含量的增加呈指数衰减趋势，衰减方程为y=0.803e–1.3284x，衰减系数（μω）为–1.328 4，R2为0.984 5。HDXRF法CdT测定结果与有机质含量呈显著的负相关关系（r=–0.955），且腐殖酸（HA）比泥炭（Peat）对测定结果的影响更大，HA与测定结果的校正方程为y=–1.555x +0.780，R2为0.934 4。土壤类型对HDXRF法CdT测定结果存在一定的影响，相对于红壤和水稻土，灰钙土的测定结果与传统实验室分析方法测定结果更接近。总之，虽然HDXRF法CdT测定结果受多种因素影响，但通过校正模型校正，其校正结果的可靠性能够满足Cd污染农田土壤精准调查需求。  相似文献   

2.
为精确测定、准确模拟阿克苏地区滴灌枣树腾发过程,基于大型称重式蒸渗仪测定枣树全生育期逐时及逐日腾发强度（ET）,利用水量平衡方程、PM公式及经典统计原理,分析不同时间尺度下叶面积指数（LAI）、气象因素[温度（I）、风速（V）、净辐射（Rn）]、表层土壤含水率（W）与枣树腾发强度的相关关系并建立预测模型。结果表明：枣树日内腾发强度呈单峰型变化趋势,夜间变化幅度较小且腾发贡献率低。枣树全生育期逐日腾发强度变化呈先增大后减小的趋势,花期的腾发强度最大,为4.42 mm·d-1;全生育期腾发总量为640.83 mm,其中花期和果实生长发育期耗水量占比较大,分别为38.61%和32.72%。在小时和日时间尺度上,影响腾发强度的主要因素不完全相同,且影响程度有所差异。综合考虑各影响因素,以萌芽期、花期、果实发育期为基础,分别建立以小时、日尺度下估算腾发强度的经验模型ET1（h）=0.153+0.004T+0.012V+0.176Rn+0.002W+0.067LAI、ET2（d）=-3.325+0.081T+0.163Rn+0.069W+2.089LAI,拟合度R2均在0.7以上,以果实发育期与成熟期数据对模型进行检验,纳什效率系数分别达0.63、0.80。经偏相关检验,冠层净辐射（Rn）对两种尺度的腾发强度均影响最显著,因此以枣树全生育期数据量为基础,仅建立冠层净辐射（Rn）与腾发强度的回归模型ET1（h）=-0.063 3Rn2+0.361 2Rn—0.003 7、ET2（d）=-0.018 3Rn2+0.684 7Rn–1.642 1,R2分别为0.704 7与0.743 6,可满足缺少数据支撑情况下的腾发过程估算。这些模型明确了阿克苏地区滴灌枣树腾发机制及影响程度,可为水分管理精准化提供计算基础。  相似文献   

3.
高光谱遥感是监测土壤盐渍化的重要手段之一，但野外光谱反射率易受土壤水分的影响，导致盐分监测精度难以保证。为有效消除水分因素，提高土壤含盐量反演精度，该研究以银川平原盐渍化土壤为研究对象，以野外土壤光谱反射率（reflectance，Ref）和实测土壤含盐量为数据源，分析不同含水率的土壤光谱特征，将反射率经过一阶微分（first derivative of reflectance，FDR）、正交信号校正（orthogonal signal correction，OSC）和一阶微分-正交信号校正（first derivative of reflectance - orthogonal signal correction，FDR-OSC）变换，分析各光谱数据与含盐量、含水率的相关性，确定最佳“除水”方法，然后基于支持向量机（support vector machine，SVM）建立土壤含盐量反演模型。结果表明：1）含水率与土壤光谱反射率呈反比，光谱在1 430、1 950、2 200 nm附近存在吸收带，1 950 nm附近为最主要吸收波段，且存在向长波漂移的现象。2）光谱数据与含水率相关性由强到弱的顺序为：Ref、OSC、FDR、FDR-OSC；与含盐量相关性由强到弱的顺序为：FDR-OSC、FDR、OSC、Ref。3）基于FDR-OSC“除水”的SVM含盐量模型决定系数Rc2、Rp2和相对分析误差（relative prediction deviation，RPD）分别达到0.952、0.960和5.04，具有极强的拟合和反演能力。研究结果可为银川平原及同类地区土壤含盐量的精准监测提供科学依据。  相似文献   

4.
Intensification of grazed grasslands following conversion from dryland to irrigated farming has the potential to alter ecosystem carbon (C) cycling and affect components of carbon dioxide (CO2) exchange that could lead to either net accumulation or loss of soil C. While there are many studies on the effect of water availability on biomass production and soil C stocks, much less is known about the effect of the frequency of water inputs on the components of CO2 exchange. We grew Bermuda grass (Cynodon dactylon L.) in mesocosms under irrigation frequencies of every day (I1 treatment, 30 d), every two days (I2 treatment, 12 d), every three days (I3 treatment, 30 d), and every six days (I6 treatment, 18 d, after I2 treatment). Rates of CO2 exchange for estimating net ecosystem CO2 exchange (FN), ecosystem respiration (RE), and soil respiration (RS) were measured, and gross C uptake by plants (FG) and respiration from leaves (RL) were calculated during two periods, 1–12 and 13–30 d, of the 30-d experiment. During the first 12 d, there were no significant differences in cumulative FN (mean ±standard deviation, 61 ±30 g C m-2, n = 4). During the subsequent 18 d, cumulative FN decreased with decreasing irrigation frequency and increasing cumulative soil water deficit (W), with values of 70 ±22, 60 ±16, and 18 ±12 g C m-2 for the I1, I3, and I6 treatments, respectively. There were similar decreases in FG, RE, and RL with increasing W, but differences in RS were not significant. Use of the C4 grass growing in a C3-derived soil enabled partitioning of RS into its autotrophic (RA) and heterotrophic (RH) components using a 13C natural abundance isotopic technique at the end of the experiment when differences in cumulative W between the treatments were the greatest. The values of RH and its percentage contributions to RS (43% ±8%, 42% ±8%, and 8% ±5% for the I1, I3, and I6 treatments, respectively) suggested that RH remained unaffected across a wide range of W and then decreased under extreme W. There were no significant differences in aboveground biomass between the treatments. Nitrous oxide (N2O) emission was measured to determine if there was a trade-off effect between irrigation frequency and increasing W on net greenhouse gas emission, but no significant differences were found between the treatments. These findings suggest that over short periods in well-drained soil, irrigation frequency could be managed to manipulate soil water deficit in order to reduce net belowground respiratory C losses, particularly those from the microbial decomposition of soil organic matter, with no significant effect on biomass production and N2O emission.  相似文献   

5.
为探讨磁化水灌溉处理在促进植物生长、提高植株重金属耐受性方面的作用机制,本研究采用随机区组试验设计,研究了镉胁迫（0 μmol·L-1、50 μmol·L-1、100 μmol·L-1）下磁化水灌溉处理对1 a生欧美杨''I-107''光合特性、叶绿素荧光动力学参数及生长特性的影响。结果表明：1）镉胁迫会显著降低植株高生长和根茎叶干物质量;低浓度（50 μmol·L-1）镉处理促进根系直径及体积增大（P<0.05）,高浓度（100 μmol·L-1）则会抑制根系各形态参数;镉胁迫下欧美杨叶绿素b和类胡萝卜素含量分别降低12.50%、43.24%和19.27%、46.37%（P<0.05）,净光合速率（Pn）、蒸腾速率（Tr）、胞间二氧化碳（Ci）分别降低13.68%和33.68%、8.07%和27.81%、5.00%和14.99%（P<0.05）,同时,PSⅡ潜在活性（Fv/Fm）、最大光化学速率（Fv/Fo）、光合性能指数（PIabs）和量子产额（φEo）均有不同程度降低。2）磁化水灌溉提高镉胁迫植株高生长及根茎叶干物质量,增加植株根系长度及表面积;同时,叶绿素a、叶绿素b和类胡萝卜素含量在0 μmol·L-1和100 μmol·L-1镉胁迫下分别提高16.99%、40.20%,8.67%、39.10%和17.32%、50.52%（P<0.05）;Gs、Ci及WUE显著升高,Tr则降低24.20%、23.33%、12.06%（P<0.05）;另外,Fv/Fm、Fv/Fo、PIabs显著升高（P<0.05）。综上所述,磁化水灌溉处理有助于提高镉胁迫下欧美杨幼苗光合色素含量,维持光合机构功能,增强光合碳同化速率,减轻镉胁迫对植株生长发育的抑制。  相似文献   

6.
使用双针热脉冲(dual probe heat pulse, DPHP)测定冻土热特性时施加热脉冲后会导致加热探针周围的冰融化,使用目前常用的仅考虑热传导（忽略融化相变、冰水两相分界面）的解析解处理DPHP温度数据,会导致在-5 ℃至0 ℃温度范围内无法准确测量热导率 (λ) 和比热 (Cv)。为了能够准确测定冻土的 λ 和 Cv,有必要考虑DPHP加热过程中引起的冰融化的相变潜热。该研究基于COMSOL仿真软件模拟了考虑相变潜热、相变区间以及移动冰水界面的DPHP测量过程,采用随温度非线性变化的真实冻土热特性进行模拟,并与真实冻土的DPHP测量数据对比。结果表明：1）COMSOL仿真在不考虑相变条件下与无限线性热源模型结果完全吻合（R2 = 0.9989）;2）当土壤初始温度低于-5 ℃时,考虑相变发生的COMSOL仿真能够准确模拟试验结果,表现出较高的相关性（R2 > 0.93）,在-2 ～ 0 ℃的土壤初始温度范围内,无限线性热源模型的结果与试验测量显著偏离（R2 < 0.0013）;3）在不同土壤初始温度下,相变温度为-1.5 ～ -0.5 ℃的仿真结果与试验数据具有较高的相关性（R2 > 0.7）。本研究结果检验了有限元仿真用于真实冻土DPHP研究的可行性,可为准确预测冻土热特性的研究提供方法。  相似文献   

7.
中国陕西省施有机肥黄土NH4+固定的热力学性质   总被引：3，自引：0，他引：3  
Some thermodynamic properties of NH4+ fixation by loess soil in plowing and clay layers are discussed. The results indicate that the four ion adsorption equations commonly used can describe the properties of NH4+ fixation in these soils under constant temperature. Among the four adsorption equations, the single-surface Langmuir equation is the best. When the concentration of NH4Cl solution is 10-1 mol below, the Freundlich equation can be used. The changes of apparent standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) illustrate that NH4+ fixation in soil is an endothermic adsorption and spontaneous reaction, and the process can be enhanced by a higher temperature and clay content in soil. The "proper value of NH4+ fixation by soil (K1 × qm) increased with increasing clay content and temperature. The heat of NH4+ fixation in soil (Qm) confirms the conclusions made in this paper.  相似文献   

8.
为揭示粗颗粒土壤坡面侵蚀机理,采用湖北通城县、江西赣县、福建长汀县、广东五华县4个样地的4种粗颗粒土壤（分别定义为TCA、GXA、CTA、WHA）进行室内模拟降雨试验,研究粗颗粒土壤坡面侵蚀过程及侵蚀泥沙颗粒组成的变化规律。结果表明：（1）4种土壤的地表径流随着降雨时间的增长呈现出先增加后递减并趋于稳定的规律;（2）4种土壤的侵蚀特征存在差异,土壤侵蚀速率表现为WHA>TCA>GXA>CTA;（3）4种土壤的侵蚀泥沙中颗粒分布百分比大小均为砂粒>黏粒>粉粒>砾石。不同土壤侵蚀泥沙富集率表现出明显差异;（4）水流功率与土壤侵蚀速率的相关性显著,用幂函数可以准确描述其关系。在表达式中引入土壤黏粒含量、砾石含量后模型更加可靠（Dr=0.001ω1.163Cl-4.069,R2=0.82;Dr=0.003ω1.149Gr-1.934,R2=0.84）,提高了模型预测土壤侵蚀速率的精度,在实际应用中具有更广的适应范围与现实价值。  相似文献   

9.
半干旱黄土地区幼龄侧柏叶蒸腾的数学模型   总被引：5，自引：3，他引：5       下载免费PDF全文
 通过人工控制水分,形成单株幼龄侧柏的不同土壤水分梯度环境。在自然环境下对侧柏叶片定时、定位进行蒸腾速率及林冠层的光照、空气温度、空气湿度、叶水势和土壤水分等因子的同步观测。蒸腾速率与各个因子的相关分析表明:黄土半干旱地区侧柏蒸腾速率ηt/(μg·cm-2·s-1)与光照强度E/(μmol·m-2·s-1)、空气饱和差pv/kPa、叶水势Ψ/kPa、气温t/℃的关系可以分别表示为:ηt=>αEb,ηt=αpvb,ηt=αψb,ηt=αt2+bt+c;侧柏的蒸腾速率ηt与气孔阻力Rs/(s·cm-1)和土壤含水量W/％有密切关系,可以分别表示为:ηt=α+bW+cW2+dW3,Rs=α+bW+cW2+dW3。用气温、空气饱和差、叶水势3个因素建立了半干旱黄土地区幼龄单株侧柏蒸腾速率的非线性指数预测模型:ηt=0.6950exp（0.03158t-14.2492/pv+0.7606/Ψ）,经检验获得了满意的数值模拟结果。  相似文献   

10.
长江中下游地区夏季温室黄瓜冠层温度模拟与分析研究   总被引：3，自引：0，他引：3  
根据作物冠层能量平衡原理，建立了以温室内温度、湿度、冠层净辐射等为变量的温室作物冠层温度的模拟模型，并利用实测资料对模型的可靠性进行了检验，同时就温室内部温度、冠层净辐射、蒸腾速率对冠层温度的影响进行了敏感性分析。结果表明：模型能较好地预测长江中下游地区温室作物冠层温度，模型对该地区夏季(2002年6月24至7月12日，梅雨季节)温室内作物冠层温度预测值与实测值的决定系数(R2)和标准误(SE)分别为：0.8321，0.0037℃；建立的温室内部温度、相对湿度、净辐射和作物蒸腾速率的多元线性回归模型，其决定系数(R2)和标准误(SE)分别为：0.9996，0.8829℃；通过敏感性解释因子的分析表明，作物冠层温度对温室内部温度最为敏感，室内温度是预测冠层温度的主要因子。  相似文献   

11.
低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响   总被引：2，自引：2，他引：0  
【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。  相似文献   

12.
Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.  相似文献   

13.
正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,  相似文献   

14.
“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.  相似文献   

15.
Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.  相似文献   

16.
The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.  相似文献   

17.
Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.  相似文献   

18.
Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L?1 nitric acid (HNO3) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L?1 ammonium acetate (NH4OAc) and 1.0 mol L?1 HNO3 extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.  相似文献   

19.
Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.  相似文献   

20.
To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号