种植作物条件下非饱和土壤中水盐的动态实验和数值模拟研究

A laboratory salt-water dynamics experiment using unsaturated soils in packed silt loam and clay soil columns with different soil texture profiles and groundwater levels under crops were conducted to study the changes of salt-water dynamics induced by water uptake of crops and to propose the theoretical basis for the regulation and control of salt-water dynamics as well as to predict salinity levels. The HYDRUS 1D model was applied to simulate the one-dimensional movement of water and salt transport in the soil columns. The results showed that the salts mainly accumulated in the plow layer in the soil columns under crops. Soil water and salt both moved towards the plow layer due to soil water absorption by the crop root system. The salt contents in the column with lower groundwater were mostly greater than those with high groundwater. The water contents in the soil columns increased from top to the bottom due to plant root water uptake. The changes in groundwater level had little influence on water content of the root zone in the soil columns with crop planting. Comparison between the simulated and the determined values showed that model simulation results were ideal, so it is practicable to do numerical simulation of soil salt and water transport by the HYDRUS 1D model. Furthermore, if the actual movement of salt and water in fields is to be described in detail, much work needs to be done. The most important thing is to refine the parameters and select precise boundary conditions.     

地膜覆盖滴灌棉田土壤上水分动态的数值模拟

Drip irrigation under plastic mulch has been widely applied in arid Northwest China as a water-saving irrigation technology.A comprehensive knowledge of the distribution and movement of soil water in root zone is essential for the design and management of irrigation regimes.Simulation models have been proved to be efcient methods for this purpose.In this study,the numerical model Hydrus -2D was used to simulate the temporal variations of soil water content in a drip irrigated cotton field under mulching.A concept of partitioning coefcient,calibrated to be 0.07,was introduced to describe the efect of plastic mulch on prevention of evaporation.The soil hydraulic parameters were optimized by inverse solution using the field data.At the optimized conditions,the model was used to predict soil water content for four field treatments.The agreements between the predictions and observations were evaluated using coefcient of determination (R2) and root mean square error (RMSE).The results suggested that the model fairly reproduced the variations in soil water content at all locations in four treatments,with R2 ranging from 0.582 to 0.826 and RMSE from 0.029 to 0.050 cm3 cm-3,indicating that the simulations agreed well with the observations.     

Salt—Water Dynamics in Soils：Ⅲ.Effect of Crop Planting

Through a simulation test conducted with soil columns (61.8cm in diameter) in field condition,effect of crop planting upon the regulation of salt-water dynamics in soils was studied by monitoring of salt-water dynamics in situ,using soil salinity sensors and tensiometers.The results indicated that the amount of water absorbed by crops from the soil was generally larger than the decrement of water consumption from soil surface evaporation reduced by the crop covering the soil surface and improving the soil structure,therefore,under the conditions of crop growing and non-irrigation,water content in soil profile was less than that without crop growing,and the gradient of negative pressure of soil water in soil profile especially in the root zone was enlarged,thus causing the water flowing from subsoils into root zone and increasing the groundwater moving upwards into soil layer via capillary rise,so that the groundwater evaporation increased.Consequently,under the condition of crop growing,the salt was mainly accumulated towards the root zone rather than to the top soil.the accumulating rate of salt in groundwater via capillary rise of soil water to subsoils was increased thereby.     

内蒙古草原碳、氮储量:气候与土壤质地的关系

Understanding the spatial variability of soil carbon(C) storage and its relationship with climate and soil texture is critical for developing regional C models and for predicting the potential impact of climate change on soil C storage. On the basis of soil data from a transect across the Inner Mongolian grasslands, we determined the quantitative relationships of C and nitrogen(N) in bulk soil and particle-size fractions(sand, silt, and clay) with climate and soil texture to evaluate the major factors controlling soil C and N storage and to predict the effect of climate changes on soil C and N storage. The contents of C and N in the bulk soil and the different fractions in the 0–20 and 20–40 cm soil layers were positively correlated with the mean annual precipitation(MAP) and negatively correlated with the mean annual temperature(MAT). The responses of C storage in the soil and particle-size fractions to MAP and MAT were more sensitive in the 0–20 cm than in the 20–40 cm soil layer. Although MAP and MAT were both important factors influencing soil C storage, the models that include only MAP could well explain the variation in soil C storage in the Inner Mongolian grasslands. Because of the high correlation between MAP and MAT in the region, the models including MAT did not significantly enhance the model precision. Moreover, the contribution of the fine fraction(silt and clay) to the variation in soil C storage was rather small because of the very low fine fraction content in the Inner Mongolian grasslands.     

沙漠地区滴灌条件下地膜覆盖对玉米生长的影响

Plastic cover, as a method to minimize soil water evaporation and improve water use efficiency, was used for corn during the whole growing period in a desert area. Field studies were conducted to determine the effect of plastic covering management on corn growth and rooting pattern and its relationship with changes in climate. Four treatments, 0) bared soil without cover, 1) covering one side of the crop, 2) covering both sides of the crop, and 3) covering the surface totally, were established on a sandy loam soil. Results showed that treatment 0 was significantly different from others and revealed that plastic covering was not always good to corn growth. Improper usage of plastic cover might weaken root development and thereafter lower the total yield of the crop. Suitable practices combining different methods discussed could not only improve water use efficiency but also increase the crop yield.     

苏打盐碱水灌溉的土壤添加石膏肥和有机肥后水溶性碳和微生物碳研究

Microbial biomass carbon (MBC), a small fraction of soil organic matter, has a rapid turnover rate and is a reservoir of labile nutrients. The water-extractable carbon pools provide a fairly good estimate of labile C present in soil and can be easily quantified. Changes in soil MBC and water-extractable organic carbon pools were studied in a 14-year long-term experiment in plots of rice-wheat rotation irrigated with canal water (CW), sodic water (SW, 10-12.5 mmol c L-1 residual sodium carbonate), and SW amended with gypsum with or without application of organic amendments including farmyard manure (FYM), green manure (GM), and wheat straw (WS). Irrigation with SW increased soil exchangeable sodium percentage by more than 13 times compared to irrigation with CW. Sodic water irrigation significantly decreased hot water-extractable organic carbon (HWOC) from 330 to 286 mg kg-1 soil and cold water-extractable organic carbon (CWOC) from 53 to 22 mg kg-1 soil in the top 0-7.5 cm soil layer. In the lower soil layer (7.5-15 cm), reduction in HWOC was not significant. Application of gypsum alone resulted in a decrease in HWOC in the SW plots, whereas an increase was recorded in the SW plots with application of both gypsum and organic amendments in both the soil layers. Nevertheless, application of gypsum and organic amendments increased the mean CWOC as compared with application of gypsum alone. CWOC was significantly correlated with MBC but did not truly reflect the changes in MBC in the treatments with gypsum and organic amendments applied. For the treatments without organic amendments, HWOC was negatively correlated with MBC (r = 0.57*) in the 0-7.5 cm soil layer, whereas for the treatments with organic amendments, both were positively correlated. Irrigation with SW significantly reduced the rice yield by 3 t ha-1 and the yield of rice and wheat by 5 t ha-1 as compared to irrigation with canal water. Application of amendments significantly increased rice and wheat yields. Both the rice yield and the yield of rice and wheat were significantly correlated with MBC (r = 0.49**-0.56**, n = 60). HWOC did not exhibit any relation with the crop yields under the treatments without organic amendments; however, CWOC showed a positive but weak correlation with the crop yields. Therefore, we found that under sodic water irrigation, HWOC or CWOC in the soils was not related to MBC.     

应用CropSyst模型模拟东北黑土区春小麦生长

Available water and fertilizer have been the main limiting factors for yields of spring wheat, which occupies a large area of the black soil zone in northeast China; thus, the need to set up appropriate models for scenario analysis of cropping system models has been increasing. The capability of CropSyst, a cropping system simulation model, to simulate spring wheat growth of a widely grown spring cultivar, ‘Longmai 19＇, in the black soil zone in northeast China under different water and nitrogen regimes was evaluated. Field data collected from a rotation experiment of three growing seasons （1992- 1994） were used to calibrate and validate the model. The model was run for 3 years by providing initial conditions at the beginning of the rotation without reinitializing the model in later years in the rotation sequence. Crop input parameters were set based on measured data or taken from CropSyst manual. A few cultivar-specific parameters were adjusted within a reasonable range of fluctuation. The results demonstrated the robustness of CropSyst for simulating evapotranspiration, aboveground biomass, and grain yield of ＇Longmai 19＇ spring wheat with the root mean square errors being 7%, 13% and 13% of the observed means for evapotranspiration （ET）, grain yield and aboveground biomass, respectively. Although CropSyst was able to simulate spring production reasonably well, further evaluation and improvement of the model with a more detailed field database was desirable for agricultural systems in northeast China.     

Field-scale spatial variability of soil calcium in a semi-arid region: Implications for soil erosion and site-specific management

Excess calcium(Ca) in soils of semi-arid and arid regions has negative effects on soil structure and chemical properties, which limits the crop root growth as well as the availability of soil water and nutrients. Quantifying the spatial variability of soil Ca contents may reveal factors influencing soil erosion and provide a basis for site-specific soil and crop management in semi-arid regions. This study sought to assess the spatial variability of soil Ca in relation to topography, hydraulic attributes, and soil types for precision soil and crop management in a 194-ha production field in the Southern High Plains of Texas,USA. Soils at four depth increments(0–2, 0–15, 15–30, and 30–60 cm) were sampled at 232 points in the spring of 2017. The Ca content of each sample was determined with a DP-6000 Delta Premium portable X-ray fluorescence(PXRF) spectrometer. Elevation data was obtained using a real-time kinematic GPS receiver with centimeter-level accuracy. A digital elevation model(DEM) was derived from the elevation data, and topographic and hydraulic attributes were generated from this DEM. A generalized least-squares model was then developed to assess the relationship between soil Ca contents of the four layers and the topographic and hydraulic attributes. Results showed that topographic attributes, especially slope and elevation, had a significant effect on soil Ca content at different depths(P 0.01). In addition, hydraulic attributes, especially flow length and sediment transport index(STI), had a significant effect on the spatial distribution of soil Ca. Spatial variability of soil Ca and its relationships with topographic and hydraulic attributes and soil types indicated that surface soil loss may occur due to water or wind erosion, especially on susceptible soils with high slopes. Therefore, this study suggests that the application of PXRF in assessing soil Ca content can potentially facilitate a new method for soil erosion evaluation in semi-arid lands. The results of this study provide valuable information for site-specific soil conservation and crop management.     

一个用于分析土地覆被变化对径流机制影响的分布式月水量平衡模型

The Miyun Reservoir is the most important water source for Beijing Municipality, the capital of China with a population of more than 12 million. In recent decades, the inflow to the reservoir has shown a decreasing trend, which has seriously threatened water use in Beijing. In order to analyze the influents of land use and cover change （LUCC） upon inflow to Miyun Reservoir, terrain and land use information from remote sensing were utilized with a revised evapotranspiration estimation formula; a water loss model under conditions of human impacts was introduced; and a distributed monthly water balance model was established and applied to the Chaobai River Basin controlled by the Miyun Reservoir. The model simulation suggested that not only the impact of land cover change on evapotranspiration, but also the extra water loss caused by human activities, such as the water and soil conservation development projects should be considered. Although these development projects were of great benefit to human and ecological protection, they could reallocate water resources in time and space, and in a sense thereby influence the stream flow.     

稻田土壤甲烷排放模型: Ⅰ. 模型的建立

With an understanding of the processes of methane production, oxidation and emission, a semi-empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factors, was developed to predict methane emission from rice paddy soils. In the present model, the amount of methane transported from the soil to the atmosphere was determined by the rates of CH₄ production and an emitted fraction. The rates of CH₄ production in irrigated rice soils were computed from the availability of methanogenic substrates that are primarily derived from rice plants and added organic matter and the influence of soil texture, soil redox potential and temperature. The fraction of methane emitted was assumed to be modulated by the rice plants and declines with rice growth and development. To make it applicable to a wider area with limited data sets, a simplified version of the model was also derived to predict methane emission in a more practical manner.     

农田墒情动态二区模拟模型

为准确模拟土壤计划湿润层内墒情动态变化,基于土壤-植物-大气连续体物质能量运动及土壤水动力学的基本理论,考虑作物根系伸展和吸水特性,把土壤水分变化土层划分为随作物根系伸展而改变深度的包含主要根系的动态根区和无根系的储水区,构建了变根区墒情动态二区模型。模型根区深度随着作物根系伸展改变,以此准确表达土壤计划湿润层内墒情的动态变化;将储水区的土壤水分作为模型变量,计算根区下界面水分通量,由此间接地考虑了深层土壤水分对作物蒸发蒸腾量的影响。将模型拟合误差作为目标函数,采用自由搜索算法率定模型参数。应用建立的模型进行墒情模拟,模拟相对误差小于±5%和±10%所占的比例分别为49.09%和94.55%;经t检验和回归分析表明预测值和实测值相差不大,具有较好的一致性,决定系数为0.779,模型具有较高的模拟精度,能准确反映计划湿润层内墒情的变化。     

非充分灌溉条件下农田水分转化SWAP模拟

非充分灌溉改变了农田水分转化过程,以往的研究较少讨论作物根系层以下的土壤水分转化动态及其对作物耗水的影响。该文在北京市典型农田开展了冬小麦-夏玉米非充分灌溉试验,在对SWAP模型率定与验证基础上,模拟分析了非充分灌溉农田耗水规律与水分转化过程,并应用模型得到了研究区不同降水年型的最优非充分灌溉模式。结果表明:非充分灌溉的实施促使作物消耗大量土壤贮水,当降雨或灌溉量较小时,土壤水可占作物耗水量的46.1%;根区和储水区之间土壤水分交换明显,转化通量变化范围为-2.67～0.45mm/d,而储水区底部水分通量较小且无明显变化,根区土壤水分渗漏出现在灌溉或较大的降雨之后,储水区水分向上补给主要发生在作物需水关键期;与常规灌溉相比,最优非充分灌溉模式在丰水年、平水年和枯水年分别节水375、225和225mm,储水区底部深层水分渗漏量分别减少了89%、17%和2%。     

基于动态规划理论的棉花根长生长模拟方法

作物根系生长不仅取决于生理因素,还取决于生态环境因素,而土壤水分环境与作物根系生长之间的关系则是局部灌溉技术设计的理论依据之一。为了进一步探索影响棉花根系生长的主要因素,本文在根?冠水量平衡的基础上,结合作物系数与叶面积的关系模型、根长密度分布函数以及根系吸水效率函数,应用动态规划理论,建立了棉花根系生长模型,并以桶栽棉花试验结果进行验证。结果表明,该模型纳入了土壤水分环境、大气蒸腾力和叶面积等影响根系生长的因子,具有揭示根系生长耗水机理的作用。该模型模拟出的棉花总根长变化趋势与实测结果基本一致,当以多年月平均参考蒸散量(ET0)作为输入条件时,模拟结果总体误差为15.41%,可以用于工程设计。对模型敏感性分析结果表明,所建模型能够反映棉花根?叶生长的同步性,以及进入生殖生长期以后根—叶之间的水量平衡关系。棉花根系生长对土壤水分环境变化的敏感性高于对叶面积变化的敏感性,体现了棉花根系生长的机理,建模方法可行。本文研究成果对完善局部灌溉技术中灌溉制度的设计理论具有重要意义。     

河套灌区土壤水盐和作物生长的HYDRUS-EPIC模型分布式模拟

土壤水盐是影响干旱灌区作物产量的主要因素。分布式模型可综合考虑土壤、水文和气象因子在灌区的时空变异特征,为评估区域尺度土壤水盐与作物生长状况提供有效工具。该文以河套灌区解放闸灌域为研究区,根据气象-土壤-作物-灌溉等因子的空间分布特征进行均质单元划分,建立基于一维农业水文模型HYDRUS-EPIC的灌区尺度分布式模型。利用2012年和2013年定点观测数据(土壤水分、盐分、叶面积指数和作物产量)进行模型率定与验证;进一步应用模型以求探明现状灌溉条件下研究区土壤水盐与作物生长状况及存在的问题。结果表明:生育期内灌区根区土壤(0~100 cm)有效饱和度为0.44~0.90,基本满足作物耗水需求;根区土壤溶液平均盐分浓度为3.1~13.5 g/L,相应地作物的相对产量为0.35~1.33,土壤盐分过高成为限制研究区作物产量的主因。为调控根区土壤水盐状况,对地下水深埋区(东北部)需进行灌水量的适宜补充,宜将浅埋区(西北、西南等)地下水平均埋深控制在1.3 m以下。     

Simulation of the impact of subsoil compaction on soil water balance and crop yield of irrigated maize on a loamy sand soil in SW Spain

Irrigation of crops in Mediterranean countries can produce some conditions that favour soil compaction processes. The SIMWASER model takes into account the effects of subsoil compaction on water balance and crop yield. The objectives of this paper were: (i) to test the mentioned model using the data set collected, during three years (1991–1993), from irrigation experiments with maize (Zea mays L., cv. Prisma) on a sandy soil (Cambisols (FAO, 1990) or Xerocrepts (USDA, 1998)) in SW Spain and (ii) to estimate the influence of subsoil compaction on soil water balance and crop yield assuming long lasting heavy subsoil compaction that may be developed under irrigation for the SW Spain conditions. The model was run to simulate soil water content, evapotranspiration, drainage below the root zone, and crop yield for the same period in which the experiment was carried out. Results of simulation were compared with the experimental results in order to know the agreement between them. The results obtained show a fairly good agreement between simulated and measured values for most of the parameters considered. For the scenario in which subsoil compaction is developed under irrigation, the results simulated by the model indicate a reduction of the rooting depth. However, the effects on water balance and crop yield in this sandy soil were not relevant under the SW Spain conditions.     

A model for estimating soil moisture changes as an aid to irrigation scheduling and crop water-use studies: II. Field test of the model

Abstract. A model was developed to estimate daily evapotranspiration and root zone soil moisture changes appropriate for scheduling irrigation, incorporating a modified version of the Penman-Monteith equation.
The model was field tested during 1992–94, for potatoes and sugarbeet, by comparing modelled root zone soil moisture changes with field measurements taken using neutron probes. The study confirmed the accuracy of the model when predicting crop water use and soil moisture change. Linear regression of measured versus modelled data exhibited a slope of 0.99 and an intercept close to and not significantly different from zero. The relationship accounted for 80% of the variation.     

畦灌不同施肥模式对夏玉米田间水氮分布的影响

为了探究夏玉米畦灌条件下适宜的灌溉施肥模式,在大田试验条件下对不同施肥方式(液施和撒施)、液施不同施肥时机和不同入畦流量下土壤水氮空间分布状况及其变化趋势进行了研究。结果表明,灌后2d土壤水分空间分布差异明显小于硝态氮,适当增大入畦流量有助于改善沿畦长方向土壤水分空间分布均匀性。灌后2d不同处理间作物有效根系层土壤硝态氮和土壤水分的贮存效率(土壤有效根系层土壤硝态氮占0—100cm土层中硝态氮的比重)变化都不明显。入畦流量相同时,液施情况下硝态氮沿畦长分布均匀性(介于86.1%~96.9%之间)高于撒施(介于89.3%~89.7%之间)。基于入畦单宽流量为4L/(s·m)、灌水至畦长33%处时均匀施肥的畦灌施肥模式,玉米根系层中土壤水氮含量比重较高,而且土壤水分与土壤硝态氮沿畦长分布均匀性最好,从而形成了有助于作物吸收的均匀的土壤水氮空间分布状态。     

HIMS模型蒸散发模块的改进及在海河流域的应用

利用流域分布式水文模型精确模拟计算和分析流域内不同植被类型实际蒸散发量及其时空分布特征,是当前流域蒸散发研究的一个前沿与难点问题。本文基于点尺度蒸散发观测试验与机理研究,对HIMS(Hydro-Informatic Modelling System)日过程模型蒸散发模块进行改进,考虑流域内植被空间分布和生长变化特性及灌溉措施的影响,利用分类汇总和分段单值作物系数法计算流域实际蒸散发,并在海河流域进行验证分析。研究结果表明:流域实际蒸散发模拟值与水量平衡法计算值相差3.4%,与原HIMS模型相比,蒸散发模拟精度提高9.2%;改进的模型对原有模型的模拟内容有所扩展,能够模拟林地蒸散发、草地蒸散发、冬小麦?夏玉米农田总蒸散发、作物有效蒸腾和土壤无效蒸发。改进后的HIMS模型能够快速模拟分析流域内不同植被类型实际蒸散发量及其时空分布特性,可为海河流域蒸散发管理提供技术支撑。     

河套灌区井渠结合膜下滴灌土壤盐分演化规律

针对内蒙古河套灌区井渠结合的问题,基于SaltMod模型建立井灌区和渠灌区水盐均衡模型,并引入含水层侧向交换量对模型进行改进,利用隆胜井渠结合试验区15 a水盐观测资料对改进的模型进行率定和验证,采用验证后的模型分析了隆胜井渠结合区在现状条件下以及在井渠结合膜下滴灌推广实施后区域的土壤盐分演化规律。结果表明,现状条件下隆胜井渠结合区土壤盐分基本稳定,尤其是渠灌区根系层盐分基本稳定,保持在较低水平,可以在长时期内满足作物生长的需求。当推广井渠结合膜下滴灌后,井灌区的生育期灌溉定额和地下水埋深对其灌溉用地根系层土壤盐分积累的影响较小,而地下水矿化度与秋浇频率的影响较大。对于井灌区,建议采用黄河水2年1次进行秋浇压盐,可以长期将土壤全盐维持在3 g/kg以下,以满足作物生长需求。     

Simulating the impact of irrigation management on the water and salt balance in drained marsh soils (Marismas, Spain)

Abstract. Using the simulation model MACRO, this paper investigates the likely consequences of reduced irrigation inputs on the water and salt balance and crop growth in a drained, saline clay in a Mediterranean climate (Marismas, SW Spain). The model was first successfully validated against field measurements of the soil water and chloride balance, water table depths and drain outflows in the 1989 growing season. Three-year simulations were then performed assuming two different irrigation applications (60 and 75% reductions from the 1989 amount) and two different frequencies (12 or 6 irrigations per growing season). The model predictions suggested that reduced irrigation may lead to up to a 15%) increase in the chloride content of the soil profile after 3 years. Also, despite overall reductions in water discharge, slight increases in chloride leaching via field drains ( c. 4 to 8%) were predicted. The model demonstrated that encroachment of salt into the soil profile may he exacerbated by the non-equilibrium nature of water flow and solute transport ('by-passing flow') in structured clays. With reduced water supply for irrigation, more frequent applications may give marginally better crop yields for the same quantity of irrigation but at the expense of slightly increasing salt concentration in the root zone.