Steam distillation and gas-liquid chromatographic determination of triallate and diallate in milk and plant tissue

A procedure based on steam distillation is described for the determination of residues of the thiocarbamate herbicides diallate and triallate. The herbicides are steam-distilled directly from aqueous suspensions of milk and plant samples and trapped in hexane. After column cleanup on either activated Florisil or silica cartridges, samples are quantitated by gas-liquid chromatography. Recoveries of diallate and triallate from milk, lettuce, peas, corn, canarygrass seed and straw, and flax straw ranged from 77 to 96%.     

基于宇宙射线缪子的土壤含水率监测

为了丰富土壤含水率的测量手段,拓展宇宙射线缪子技术在农业工程领域的应用,该研究提出了利用宇宙射线缪子监测土壤含水率的方法,即通过放置在土壤中的缪子探测器测得的宇宙射线缪子计数来反推出土壤含水率。利用蒙特卡罗程序FLUKA对不同含水率的土壤建模并进行数值模拟,得出土壤含水率的探测分辨率,进一步得到最佳的缪子探测器放置深度。结果表明,探测半径与探测器放置深度相关,将探测器放置在地表下方80 cm深度处时,探测半径为6.2 m,此时当探测时长为2 h时,对土壤含水率的探测分辨率可以达到0.1 cm3/cm3;当探测时长达到8 h时,探测分辨率可以达到0.05 cm3/cm3。相较于60、70、80、100、110、120 cm等不同深度,探测器放置在地表下方90 cm处时,在相同探测时长条件下,土壤含水率的探测分辨精度最高,达到0.038 cm3/cm3。验证试验结果表明,缪子计数值的变化可以反映出待测物质质量厚度的较小变化。相较于传统的点测量方法和宇宙射线中子法,该方法的探测范围适中（探测半径为6～8 m）,且测量结果不易受土壤密度之外的因素影响,可以作为其他监测技术的重要补充,具有广阔的应用前景。     

双极化雷达反演裸露地表土壤水分

为了快速高效地获取大面积地表土壤水分,本文提出一种适用于双极化SAR(synthetic aperture rader)的裸露地表土壤水分反演经验模型。首先通过AIEM(advanced integral equation model)模型数值模拟和回归分析,提出一种新的粗糙度参数,将2个传统的粗糙度参数简化为1个参数;然后模拟地表土壤水分与雷达后向散射系数的关系,从而建立裸露地表的经验散射模型,模型的未知参数仅为粗糙度参数和土壤体积含水量,通过双极化的雷达数据即可实现土壤水分的反演。通过2008年甘肃张掖黑河流域实测数据对模型进行了初步验证,发现在入射角大于25°时,模型反演值与实测值有着良好的相关关系(相关系数为0.745)。该模型仅需双极化的雷达数据就能实现土壤水分的反演,无需测量地面粗糙度,尤其适用于大面积干旱区域的地表土壤水分的获取。     

Temperature and moisture dependence of decomposition rates of hardwood and coniferous leaf litter

Samples of fresh (autumn) and of year-old (late summer) deciduous forest-leaf litter and humus, and of Douglas fir fine litter and humus, were wetted to known moisture content, nominally between 200 and 40% water (dry basis), and maintained at constant temperatures between 10° and 40°C. Rates of CO₂ production were measured by KOH absorption and titration. Decomposition rate was found to be a linear function of log — (water potential), and to approach a maximum near 40°C. The temperature-dependence was consistent with models based on irreversible heat inactivation of a rate-controlling enzyme, also with Eyring's “absolute reaction rate” theory for reactions controlled by a reversibly inactivated enzyme. Activation energies were 66.8–67.3 kJ mol⁻¹ for litter, and 61.4–67.5 kJ mol⁻¹ for humus decomposition; for enzyme inactivation energies were 150–154 kJ mol⁻¹.     

Effects of experimental soil moisture fluctuations on turnover rates of testacea

Experiments designed to obtain data on the quantitative effects of an artificial increase in soil moisture content during a seasonal dry period on numbers of soil Testacea were carried out in a welldrained aspen woodland soil in the Rocky Mountains of Canada. The general effect of the addition of water to the soil was to increase significantly the number of active Testacea and decrease the number of encysted forms. Numbers of active Testacea and of total living Testacea (active plus encysted forms) showed significant, positive correlation with soil moisture content. A method for the estimation of standing crop turnover and secondary production is discussed. Generation times were shorter and secondary production higher in the watered plots.     

基于NDVI优化选择的土壤水分数据同化

时间序列上遥感观测数据的准确性会对同化结果有较大的影响.该文以宁夏回族自治区固原市为例,通过北方生产力生态模犁模拟2008年5-7月逐日的土壤湿度,按照不同日期的归一化植被指数(normalized difference vegetation index,NDVI)阈值,分别利用MODIS资料计算出基于红光和近红外波段的垂直含水量指数、改进的垂直干旱指数和基于近红外波段和短波红外波段的短波红外垂直水分胁迫指数,和宁夏中南部的气象站实测土壤水分建立关系,并用不同遥感指数反演的土壤水分作为观测值进行同化.结果表明,在作物的不同生长时期,垂直含水量指数、改进的垂直干旱指数和短波红外垂直水分胁迫指数的反演效果不同,基于NDVI优化遥感反演结果,选择准确性更高的反演结果作为同化观测值,能提高同化土壤水分的精度.该研究表明在不同时间段内使用更为准确的遥感监测结果作为观测值进行同化可以提高同化的精度.     

Soil respiration during secondary succession: Influence of temperature and moisture

The development of soil respiration was investigated from the beginning of secondary succession of a newly-exposed rubble-dump cover with and without additional management. Special interest was paid to the influence of soil temperature and soil moisture. CO₂-concentrations were measured every 2 weeks for 3 yr in the field by using an air current method with conical chambers and infrared gas analysis. No significant influence of soil moisture conditions (range of soil moisture 4–80 kPa soil water suction) on respiration rates was found. Carbon dioxide evolution generally followed soil temperature patterns in both ecosystems and showed a positive correlation with temperature T at 5 cm depth (mgCO₂m^?2h^?1 = a + b (T°C)²). Moreover both plots showed the same tendency of increasing soil respiration during the first 3 yr after reclamation, in spite of great differences in vegetation structure and coverage. This change in soil respiration rates describes the succession of soil microflora.     

冻融条件下土壤中水盐运移机理探讨

土壤冻融过程中的水盐运动是冻土学研究的基本问题之一。在土壤冻融过程中,存在着水分和盐分的2次迁移过程,形成了特殊的水盐运动规律。土壤冻结过程中盐分的运动非常复杂,受土壤类型、土壤初始含水量、土壤溶液浓度、盐分组成以及冻结生成的温度、热梯度、冻结速度、冻结方向等因素影响,其迁移结果最终是上述各因素共同作用的结果。温度是导致土壤中水分迁移的驱动力,土壤冻结引起冻结带土水势降低,导致水分不断向冻层迁移,随着水分向冻层聚集,冻层以下土层中的盐分同步向上运移,整个冻层的土壤含盐量明显增加。在融化过程中,随着地表蒸发逐渐强烈,使冻结过程中累积于冻结层中的盐分,转而向地表强烈聚集,使表层的盐分含量急剧上升。     

Soil moisture monitoring at the field scale using automatic capacitance probes

The capacitance probe is an attractive device for monitoring soil moisture automatically. However, its sphere of influence is rather small (a few cubic centimetres only). We have analysed the possibility of monitoring moisture at the field scale using only a few probes (≤3). We calibrated each probe by establishing a direct relation between the field average soil moisture θ_f and the signal given by the probe. As in earlier studies, we found that a linear relation is generally suitable. A classical statistical analysis was performed to assess the error of a single probe. When replicate probes were installed, we obtained replicate estimates of θ_f. We proposed an estimator θ_f that combines all replications optimally. Three experiments each lasting several months were carried out on bare tilled fields to evaluate the probe against gravimetric measurements. Our results show that the calibrations differ significantly from one probe to another. Once calibrated, the capacitance probe provided accurate soil moisture measurements (70% of the calibration relations had residual standard deviations < 0.02m³m^?3), but it is advisable to have at least two replicate probes. Soil water storage was well estimated by combining four to seven probes to establish the moisture profile, despite the error induced by each probe. Moreover, the temporal variations in water storage were accurately measured by the probes. We found an error of 0.6 mm day^?1 (standard deviation) in daily variation of the water storage, which partly involved the error made on the reference measurements (gravimetric method).     

Soil moisture and the mycorrhizal association of Pinus radiata D. don

Five ectomycorrhizal fungi were found to have an optimum growth in Mt. Burr sand at total soil water potentials of ?300 to ?600 kPa but could grow or survive at a total water potential of ?4000 kPa when glucose was supplied exogenously. Different fungi responded differently to reduced soil water potential induced by the addition of KCl solutions to soil.Growth characteristics of mycorrhizal fungi in the rhizosphere were poorly related to growth in soil with added glucose and yeast extract. Colonisation of Pinus radiata roots by Rhizopogon luteolus was greatest at soil water contents of 13% (?120 kPa osmotic potential) and was significantly depressed at 6.5%, (?510 kPa) and at 27% (?40 kPa). Cencoccum graniforme colonised roots most at 20%, (?60 kPa). Colonisation by this fungus was depressed at soil water contents of 13 to 6.5% and at 27%.Mycorrhizal infection was greatest at soil water contents of 13% (?120 kPa osmotic potential) to 20% (?60 kPa) and was significantly depressed at 27%, (?40 kPa). The depression of fungal growth in the rhizosphere and infection at soil water contents approaching saturation is discussed in terms of soil void space and aeration problems.     

免耕条件下秸秆覆盖保墒灌溉的土壤水、热及作物效应研究

该文从目前中国干旱半干旱地区发展起来的较为成熟的保墒技术得到启迪，提出了“保墒灌溉”这一新理念。重点通过小区试验研究了免耕条件下秸秆覆盖保墒灌溉的农田效应。结果表明，覆盖处理0～50 cm土壤含水率明显高于对照，地表温度日变化趋势缓和，日最高最低温度差为12.43℃，而对照则高达50.03℃。覆盖处理耕层土壤细菌、放线菌、真菌分别是对照的1.63倍、1.68倍和1.07倍，玉米株高、茎粗和叶面积均明显大于对照，相对于覆盖处理和对照本身而言，各指标均有随灌水量的增加呈上升的趋势。覆盖处理后，玉米的光合作用速率、蒸腾速率等均大于对照，但是单叶水分利用效率却相差不大。玉米产量随灌溉水量的增加较对照平均增加22.16%、20.28%和12.75%，且基本随灌溉量的增加呈上升趋势。     

Soil biodegradation of maize root residues: Interaction between chemical characteristics and the presence of colonizing micro-organisms

Due to their direct contact with the soil, roots are exposed to colonizing micro-organisms that persist after the plant has died. These micro-organisms may affect intrinsic root-chemical quality and the kinetics of root residue decomposition in soil, or interact with soil micro-organisms during the decomposition process. The aims in this work were i) to determine the interactions between the presence of root-colonizing micro-organisms and root-chemical quality and ii) to quantify the effect of these micro-organisms on root decomposition. Roots were selected from six maize genotypes cultivated in the field and harvested at physiological maturity. The roots of two genotypes (F2 and F2bm1) had a higher N content, lower neutral sugars content and higher Klason lignin content than the other genotypes (F292, F292bm3, Mexxal, Colombus). Location of the root residue micro-organisms by scanning electron microscopy and transmission electron microscopy revealed that F2 and F2bm1 roots were more colonized than roots of the other genotypes. Electron Dispersive X-Ray microanalyses of in situ N confirmed a higher N content in the colonizing micro-organisms than in the root cell walls. Residues of F2 and F2bm1 roots decomposed more slowly and to a lesser extent than those of the other genotypes during incubation in a silty loam soil under controlled conditions (15 °C, −80 kPa). After 49 days, 40.6% of the total C from F292 was mineralized but only 20.7% of from F2bm1. These results suggest that residue-colonizing micro-organisms decompose the cell-wall sugars to varying extents before soil decomposition thereby modifying the chemical quality of the residues and their mineralization pattern in soil. Due to their high N content, colonizing micro-organisms also impact on the total N content of root residues, reducing their C to N ratio. Gamma sterilized root residues were incubated under the same conditions as non-sterilized residues to see if micro-organisms colonizing root residues could modify the action of soil micro-organisms during decomposition. Similar C mineralization rates were observed for both non-sterilized and sterilized residues, indicating that the residue micro-organisms did not quantitatively affect the activity of soil micro-organisms.     

Incorporation of triallate granules for wild oat control under dry conditions

Tests using various field implements (heavy duty cultivator, vibrashank cultivator, one-way discer, and the double disc or tandem disc) were conducted to determine if the incorporation implement affected wild oat (Avena fatua L.) control by triallate. All of the implements provided efficient control of wild oat by triallate granules, achieving up to 95% control of populations as compared to the untreated check plots. All incorporation treatments rendered triallate more effective compared to non-incorporated or surface only application. Under drought conditions the intensity of incorporation must be balanced against soil moisture losses resulting from the incorporation.     

Soil moisture affects survival of microorganisms in heated chaparral soil

Prescribed burning, the planned application of fire to reduce the hazards of wildland fuels, is coming into wider use in southern California chaparral. Soil was heated to various temperatures in factorial combination with various soil moistures to determine the direct effects of fire and soil moisture on the survival of microorganisms in chaparral soil. For fungi, mild heating increased germination of dormant forms yielding significantly higher counts than those in unheated soil. With increasing temperatures, microbe populations showed an exponential decrease. For heterotrophic soil bacteria, this decrease was summarized as a function of soil moisture and temperature. Microbial groups differed significantly in sensitivity to temperature: fungi > nitrite oxidizers > heterotrophic bacteria. Physiologically-active populations in moist soil were significantly more sensitive than were dormant populations in dry soil. The mathematical model presented shows qualitatively that more of the microbial biomass will be killed when the soil is moderately moist—as during prescribed burning—than when it is dry. Mineralization of killed microbial biomass in soil and release of plant nutrients may partially explain the increased plant growth and reduced response to fertilizer at burned sites.     

土壤二向反射特性及水分含量对其影响研究

土壤二向反射特性的研究是进行地表温度、地表反照率等方面反演必须解决的问题,同时也是全球地面覆盖遥感研究所要考虑的背景因素,对定量遥感及土壤遥感技术本身的发展有着重要意义。论文在对不同类型土壤进行室内二向反射率测定的基础上,分析了其在可见光及近红外波段随观测角度变化规律,得出以下结论:在不同的观测方位角,土壤二向反射率均随着观测天顶角的增加而增加,在垂直主平面方向是对称的;并且在后向散射方向达到最高,在前向散射方向达到最低。研究利用基于辐射传输理论的Hapke二向反射模型对不同类型土壤在不同水分含量条件下的二向反射率进行了模拟并取得了较好的结果。此外,基于实测的土壤二向反射率对Hapke模型的主要参数进行反演并研究土壤水分含量对其影响,结果表明随着土壤逐渐变干,其单次散射反照率在整个波段均呈增加的趋势,并且单次散射反照率不受测量时条件的影响。因此,论文可以为利用单次散射反照率来反演土壤水分含量提供研究基础。     

豫东平原棉田土壤水分变化规律和灌溉试验研究

为探明棉花生育期间土壤水分对产量的影响，我们在豫东平原棉田进行了土壤水分状况和灌溉的试验研究。结果表明，豫东平原棉花生育期间土壤含水率存在3个低谷，分别出现在蕾期后期、花铃期后期和吐絮期中期，即棉花移栽后的21～27 d、69～75 d和102～108 d。从棉花蕾期至花铃期土壤储水量逐步增加到较高的水平，但在花铃期进行适时、适量的灌溉，同时控制盛絮期的耗水量有利于提高产量和土壤水分的利用效率(WUE)。通过2000～2002年间棉花蕾期、花铃期、吐絮期和盛絮期的田间耗水量与产量的回归分析，得出其影响产量的系数分别为0.24、1.48、-0.12和-0.33。研究认为，棉花田间灌溉的时期对产量的效应顺序为：花铃期＞蕾期＞吐絮期＞盛絮期。     

豫东平原棉田土壤水分变化规律和灌溉试验研究

为探明棉花生育期间土壤水分对产量的影响,我们在豫东平原棉田进行了土壤水分状况和灌溉的试验研究.结果表明,豫东平原棉花生育期间土壤含水率存在3个低谷,分别出现在蕾期后期、花铃期后期和吐絮期中期,即棉花移栽后的21～27 d、69～75 d和102～108 d.从棉花蕾期至花铃期土壤储水量逐步增加到较高的水平,但在花铃期进行适时、适量的灌溉,同时控制盛絮期的耗水量有利于提高产量和土壤水分的利用效率(WUE).通过2000～2002年间棉花蕾期、花铃期、吐絮期和盛絮期的田间耗水量与产量的回归分析,得出其影响产量的系数分别为0.24、1.48、-0.12和-0.33.研究认为,棉花田间灌溉的时期对产量的效应顺序为花铃期＞蕾期＞吐絮期＞盛絮期.     

黄土山地苹果园土壤水分最大利用深度分析

有效利用果园土壤调蓄作用,是进行果园高效水肥管理的基础。该文采用中子仪与烘干法相结合,对黄土山地苹果园土壤水分进行连续9a监测,以达西定律为基础,通过实测果园土壤水分特征参数,分析了黄土山地苹果园土壤水分最大利用深度。结果表明:在有效含水率范围内,根据达西定律,理论山地苹果园土壤水分最大利用深度为3.0～5.17m。黄土山地果园不同坡向间土壤含水率差异明显,阳坡含水率较低,阴坡较高,半阴坡和半阳坡介于两者之间;根据多年实测土壤含水率变化规律,山地苹果园土壤水分最大利用深度分别为:阳坡3.0m,阴坡4.5m,半阳坡3.5m,半阴坡4.0m;在有效含水率范围内,随土壤含水率提高,土壤水分最大利用深度加大。     

Effects of gypsum-slotting on infiltration rates and moisture storage in a swelling clay soil

Abstract. Previous studies have shown marked increases in wheat yields on a swelling clay soil due to gypsumslotting compared to no-gypsum and surface gypsum applications, largely through improved aeration in the surface layers. In the present study, steady infiltration rates indicated 2-fold increases due to surface gypsum applications and 4- to 6-fold increases due to slotted gypsum. This should provide increased moisture storage and reduced soil erosion hazards during prolonged heavy rainfall periods, provided that a crust does not form under the impact of raindrops. However, gypsum-slotted lands should not be used in crop rotations which include ponded rice, due to increased potential water use and risk of rising watertables and salinization.
The effect of the 'throttle' in the upper B horizon which restricts moisture storage in the lower soil layers during short-term and prolonged ponding was reduced, but not eliminated, by surface and slotted gypsum applications. Thus the moisture contents of the lower depths in both the non-ameliorated and ameliorated soils were less than the moisture content at saturation or at -10 kPa potential even after flooding for 11 days.