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不同时间尺度下杨树人工林液流密度特征

以北京大兴区榆伐镇大兴林场沙地杨树人工林107欧美杨为研究对象,运用热扩散法(TDP)并结合HOBO自动气象站,对树干液流和林内环境进行连续定位观测。结果表明,夜间杨树液流密度差异不明显,而白天差异较大,液流密度日变化主要以单峰曲线为主,典型晴天下连日变化均值为5.61cm3/(cm2.h);不同天气状况下液流密度变化为晴天(15.18cm3/(cm2.h))>阴天(10.65cm3/(cm2.h))>雨天(4.78cm3/(cm2.h));不同月份液流密度变化均呈单峰曲线变化;季节尺度表现为夏季(13.44cm3/(cm2.h))>秋季(11.47cm3/(cm2.h))>春季(6.8cm3/(cm2.h))。杨树是华北地区和北京市适宜的树种,建议展叶期适量灌溉,蒸腾高峰期和停滞期勿灌溉,以减缓耗水。     

Infiltration in surface irrigated swelling soils

Infiltration characteristics for border strip irrigation at two sites with swelling clay soils were examined. Volume infiltrated was calculated from flow onto the field monitored with flow meters; depth of water in the soil estimated from soil samples taken before and after irrigation; and the advance profile which was used to calculate the volume infiltrated with time. Volume infiltrated was compared with volume of cracks before irrigation.Linear advance and observed crack closing supported the hypothesis that infiltration approached zero after about 10 min. Volume of cracks was less than 20% of the volume infiltrated. Wetting front was 3–10 times greater than depth of observed surface cracks. There was no significant correlation between intake opportunity time and depth of infiltration, but elevation irregularities were related to infiltration.     

Impact of a gel conditioner and water quality upon soil infiltration

Summary The interactive effects of 0.0%, 0.4%, and 0.8% of a gel conditioner, Jalma, and four waters: salt solution (SS), distilled (DW), natural sewage (SW), and well (WW) waters on swelling (S), effective mean pore radius ( ), water penetrability (), diffusivity (D), and weighted-mean diffusivity ( ) in loamy sand and loam soil columns were investigated. The diffusivities of water in untreated soil columns were nearly independent of water quality. In general for both soils, S decreased, and , , and increased with increase in water salinity and decrease in % Jalma. For the loamy sand of SS, WW, SW, and DW were reduced, respectively by 15%, 39%, 45%, and 55% due to the addition of 0.4% Jalma and by 15%, 52%, 69%, and 83% due to addition of 0.8% Jalma compared to untreated control. It was concluded that 0.4% Jalma is the optimum rate when sewage (EC=1.6 dSm^–1) or other waters of low salinity are used for irrigation and 0.8% Jalma when well water (EC =6.4 dSm^–1) is used. When the irrigation water is of high salinity (EC =42.5 dSm^–1), use of this gel conditioner is not recommended. Effective mean pore radius proved to be a reliable predictor of the multiple effects of texture, Jalma and water salinity on and .     

Analysis of several discharge rate–spacing–duration combinations in drip irrigation system

In order to study the use of water irrigation in a rational way, several combinations of discharge rate, irrigation duration and inter-emitter distances were tested. For instance, three dripper spacings of 30, 50 and 70 cm which delivered water volumes of 4, 8 and 16 l per dripper, respectively, and three discharge rates of 2, 4 and 8 l/h for each spacing, were applied.An overlapping of the wetted bulbs was observed at the end of the different irrigation experiments. The inter-dripper root-zone had an average water content of 45% and a coefficient of uniformity of 90%.The discharge rate of 2 l/h applied to a 70 cm dripper spacing was characterised by water losses of 15% due to the significant irrigation duration (8 h).From this study, we reach the following conclusions, specific to the soil type and practical culture.

• 1.The maximum irrigation duration does not exceed 4 h.
• 2.Two hours durations can be used for the different spacings, each of which was characterised by its own discharge rate.

     

Relationships between crop temperature,grain yield,evapotranspiration and phenological development in two hybrids of moisture stressed sorghum

Summary Recent studies have shown that the grain yields of corn (Zea mays L.) and wheat (Triticum aestivum L.) are related to the degree of water stress they undergo. The purpose of the study reported here was to establish relationships between crop temperature and the grain yields, phenological development, evapotranspiration rates (ET) and leaf water potential ( _l ) of two hybrids of grain sorghum (Sorghum bicolor L. Moench) subjected to varying levels of plant water stress. The study was conducted at the University of Nebraska Sandhills Agricultural Laboratory in 1978 on a Typic Ustipsamment (Valentine fine sand) soil. The sorghum hybrids used were RS 626 and NB 505. Four irrigation treatments were applied in order to subject the crops to varying levels of water stress during each of three major growth stages. Soil moisture was monitored with a neutron probe. ET was estimated with the water balance technique. Crop temperature was measured with an IR thermometer and leaf water potential was measured with a Scholander pressure bomb. Grain yields were reduced by water stress occuring at anytime during the growing season. Yield reductions were largest when stress occurred during only the grainfill period and were least when stress occurred during the entire growing season. The percentage reduction in sorghum grain yield can be described by an index involving the seasonal accumulation of the daily mid-day temperature differences between well-watered and stressed crops ( TSD). As TSD values increased, ET decreased. However, the correlation of ET with TSD was relatively low (R² = 0.60) probably due to the limited amount of data available for analysis and inaccuracies in the soil water balance method used to estimate ET. The mid-day temperature of well-watered rows ranged between 18.0 and 32.8 °C with a mid-day temperature range of about 0.5 °C between the well-watered rows in various plots for several days following an irrigation. However, in certain instances, the mid-day temperature range increased to 1–2 °C for a few days before irrigation. This suggests that certain of the rows experienced water stress and should have been irrigated earlier. Yield data support that conclusion. Range in crop temperature within a field appeared to be a sensitive indicator of crop water stress in sorghum. No significant difference in the phenological development of sorghum resulted from water stress except in one NB 505 plot in which plants were stressed throughout the entire season. In that plot, the stressed plants lagged in development behind non-stressed plants by approximately ten days. The differences in mid-day leaf water potentials ( _l ) and crop temperatures (T) between stressed and non-stressed vegetation were examined. As T increased up to about 4 °C, _l , also increased. Beyond that point, _l decreased while T continued to increase. This behavior was attributed to stomatal closure which permitted an increase in _l of the stressed plants (hence reducing _l ) even as T continued to increase.Published as Paper No. 6551, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under Regional Research Project 11–33 and Nebraska Agricultural Experiment Station Project 11–50. The work upon which this publication is based was supported in part by funds provided by the Office of Water Research and Technology B-044-NEB, US Department of the Interior, Washington, DC, as authorized by the Water Research and Development Act of 1978. This article was sponsored in part by the Nebraska Water Resources Center, Institute of Agriculture and Natural Resources, University of Nebraska-LincolnResearch Assistant, Associate Professor, Research Assistant, and Associate Professor, University of Nebraska, Lincoln. Contents of this puplication do not necessarily reflect the views and policies of the Office of Water Research and Technology, US Dept. of the Interior, nor does mention of trade names or commercial products constitute their endorsement or recommendation for use by the United States Government     

Pressure chamber procedures for leaf water potential measurements of cotton

Summary Measurement of leaf water potential ( _l ) with a pressure chamber is usually regarded as a reliable and practical field technique. However, recent evidence indicates that results depend on the measurement techniques employed. Field experiments were conducted to identify the magnitude and sources of error affecting pressure chamber measurements of _l in cotton (Gossypium hirsutum L.) and to develop an accurate and operationally flexible procedure. Water potential of bare cotton leaves was about 0.2 MPa less than aluminum foil wrapped leaves when the elapsed time between excision to chamber pressurization was less than 30 s. The water potential of intact leaves increased 0.3 MPa after 15 s of enclosure in aluminum foil. 5 to 30 min of enclosure were sufficient to reach equilibrium between _l and water potential within the plant stem. Aluminum foil wrapped leaves maintained their _l for 2 h stored in a humid, dark box at 21–28 °C while wet wrapped (cheesecloth) or bare leaf _l increased after one hour because of hydration. An accurate and operationally flexible _l measurement procedure, suitable for large scale sampling, was defined.Contribution from the USDA-ARS, Water Management Research Laboratory, 2021 S. Peach, Fresno, CA 93727 and the Dept. of Land, Air and Water Resources, University of California, Davis, CA 95616, USA     

Irrigation scheduling in a mature peach orchard using tensiometers and dendrometers

Three trickle irrigation schedules, two of which were scheduled according to soil water potential ( soil) (tensiometer method) and daily stem contraction (DSC) (dendrometer method) respectively and the other one was a schedule of restricted water supply, were applied to a mature peach orchard.The annual water application based on soil was greater than that based on DSC. However, tree growth, fruit size and leaf water potential (leaf) on the trees in the dendrometer scheduling plot did not differ from those in the tensiometer scheduling plot while the premature fruit drop and fruit bud initiation were greatly different. The restricted water supply treatment limited significantly both tree and fruit growth. In addition, the lower leaf was observed on the trees in this plot.Further study shows that use of the dendrometer method for scheduling irrigation satisfies the water needs of the plant and that the tensiometer method is less accurate.Abbreviations leaf leaf water potential - soil soil water potential - DSC daily stem contraction - LVDT linear variable displacement transducer - PET potential evapotranspiration     

Root system parameters determining water uptake of field crops

Summary The distribution of a crop rooting system can be defined by root length density (RD), root length (RL) per soil layer of depth z, sum of root length (SRL) in the soil profile (total root length) or rooting depth (z _r . The combined influence of these root system parameters on water uptake is not well understood. In the present study, field data are evaluated and an attempt is made to relate a daily maximum water uptake rate (WU_max) per unit soil volume as measured in different soil layers of the profile to relevant parameters of the root system. We hypothesize that local uptake rate is at its maximum when neither soil nor root characteristics limit water flow to, and uptake by, roots. Leaf area index and the potential evapotranspiration rate (ET _p ) are also important in determining WU_max, since these quantities influence transpiration and hence total crop water uptake rate. Field studies in Germany and in Western Australia showed that WU_max depends on RD. In general, there was a strong correlation between the maximum water uptake rate of a soil layer (LWU_max) normalized by ET _p and RL normalized by SRL. The quantity LWU_max · ET _p ^-1 was linearly related to (RL/SRL)^1/2. The data show that the single root model will not predict the influence of RD on WU_max correctly under field conditions when water-extracting neighboring roots may cause non-steady-state conditions within the time span of sequential observations. Since the rooting depth z _r was linearly related to (SRL)^1/2, the relation: LWU_max · ET _p ^-1 = f (RL^1/2/z _r ) holds. Furthermore it was found that the maximum specific uptake rate per cm root length UR_max was inversely related to RD^1/2 and to SRL^1/2 or z _r of the profile. Observed high specific uptake rates of shallow rooted crops might be explained not only by their lower RD-values but also by the additional effect of a low z _r . The relations found in this paper are helpful for realistically describing the sink term of dynamic water uptake models.Growing plants extract water from the soil to meet transpiration needs. Rates of transpiration and of water uptake are set by evaporative demand and by plant and soil factors which influence capacity to meet that demand. These factors include crop canopy size and leaf characteristics, root system characteristics and hydraulic properties of the soil and the soil-root interface. Soil and root system properties vary with depth and all factors vary in time, so that parameters related to them require constant updating over a crop season.Dynamic simulation models describe water uptake by root systems under field conditions as a function of soil depth and time. Many of these simulation approaches are based on Gardner's (1960) single root model (Feddes 1981). These simulation procedures follow the assumption that water uptake is proportional to a difference in water potential between the bulk soil and the root surface or the plant interior, to the hydraulic conductivity of the soil-plant system and to the effectiveness of competing roots in water uptake. The effectiveness factor accounts more or less empirically for the influence of various root system parameters on water uptake such as percentage of active roots absorbing water, root surface permeability, root length density determining the distance between neighbouring roots, or total root length and depth of the root system. Such models however, will not always reflect correctly the influence of root system characteristics on water uptake since these assumptions have rarely been tested under field conditions. In many instances, there is better agreement between simulated and measured total water use of plants than between predicted and observed water depletion by roots within individual layers of the soil profile (Alaerts et al. 1985).Water uptake by an expanding root system as a function of depth and time has been studied under field conditions for several crops (listed in Herkelrath et al. 1977a; Feddes 1981; Hamblin 1985). They show that the dynamics of water uptake depend on root length density and the availability of soil water. However, the combined influence of root length density, total root length and rooting depth on the water uptake pattern has not been assessed. An evaluation of root system parameters with respect to soil water extraction should aid our understanding of how roots perform under field conditions and may assist our efforts to formulate the water uptake function of roots in dynamic simulation studies more realistically.The aim of the present investigation is to develop an approach that relates measured water uptake rates to relevant parameters of the root systems. This approach will be confined to situations where water uptake in a soil layer is not restricted by unfavorable soil conditions, such as in wet soil, by insufficient aeration and, in dry soil, by reduced water flow towards roots or by increased contact resistance (Herkelrath et al. 1977b). We will define a maximum water uptake rate WU_max that is neither soil-limited nor appreciably limited by the decreasing permeability of aging roots. This WU_max will be related to relevant root system parameters as they exist when WU_max is observed. Hence, water uptake by roots in a very wet, as well as in a dry soil, has been excluded from consideration.     

考虑日光温室空间异质性的黄瓜叶片湿润时间估算模型研究

叶片湿润时间（LWD）是植物病害模型的重要输入变量之一，它与许多叶部病原菌的侵染有关，影响病原侵染和发育速率。为了准确地预测日光温室黄瓜病害的发生时间和方位，本研究于2019年3月和9月在北京两个不同类型日光温室内按照棋盘格法设置了9个采样点部署温湿光传感器和目测叶片湿润时间，每隔1 h采集一次温度、湿度、辐射和叶片湿润数据进行定量估算分析。分析结果表明：BP神经网络模型在两个温室的试验条件下获得了相似的准确度（ACC为0.90和0.92），比相对湿度经验模型估算叶片湿润时间的准确度（ACC为0.82和0.84）更高，平均绝对误差MAE分别为1.81和1.61 h，均方根误差RSME分别为2.10和1.87，决定系数R²分别为0.87和0.85；在晴天和多云天气条件下，叶片湿润时间的空间分布总体规律是南部＞中部＞北部，南面是叶片湿润平均时间（12.17 h/d）最长的区域；由东向西方向上，叶片湿润时间的空间分布总体规律是东部＞西部＞中部，中部是叶片湿润平均时间（4.83 h/d）最短的区域；雨天的叶片湿润平均时间比晴天和多云长，春季和秋季分别为17.15和17.41 h/d。这些变化和差异对温室黄瓜种群水平方向的叶片湿润时间分布具有重要影响，与大多数高湿性黄瓜病害的发生规律密切相关。本研究为预测温室黄瓜病害分布提供了有价值的参考，对控制病害流行和减少农药使用具有重要意义，提出的区域化分析温室内叶片湿润时间的方法，可以为模拟日光温室叶片湿润时间的空间分布提供参考。     

供水水头和灌水器对负压灌溉土壤水运移的影响

研究了不同供水水头（H）（0.5、0、-0.5、-1、-2m）及不同孔径的负压灌水器（3～4、5～6μm）对负压灌溉出水量及土壤水分运移的影响。试验结果表明,不同处理中,湿润锋运移规律相似,湿润体近似为椭球体。当灌溉时间相同时,湿润体体积随供水水头的减小而减小。累计入渗量、最大水平和垂直湿润距离随高程差呈幂函数变化。灌...     

Bypass flow and its role in leaching of raised beds under different land use types on an acid sulphate soil

A better understanding of leaching processes in raised beds is useful in assessing management options for acid sulphate soils. Field and laboratory studies were carried out to quantify the effects of soil physical properties and bypass flow on leaching processes of new, 1-year-old and 2-year-old raised beds for yam and pineapple cultivation in a Typic Sulfaquept in Tien Giang, Vietnam. The methylene blue staining technique was used to characterize the water-conducting pores in terms of number, stained area, and total pore perimeter at 10 cm depth intervals of six 1 × 1 m subplots. Undisturbed 20 cm X 25 cm soil cores taken from the raised beds were subjected to three 30 mm h⁻¹ rains. Volume, aluminum and sulphate concentration of the outflows were monitored. Consolidation with time decreased the area and perimeter of water-conducting pores in 2-year-old pineapple beds to about a third, and bypass flow rate to about 80% of those in newly constructed beds. Consolidation did not affect macropore network geometry in yam beds because they were subjected to annual tillage and yam tubers were uprooted regularly. A13⁺ and SO₄²⁻ concentrations in the outflows of the newly constructed and 1-year-old raised beds were higher in pineapple, while those in 2-year raised beds were higher in yam.