砂田抑制蒸发功能随覆砂年限的演变规律

【目的】研究压砂覆盖(砂田)保温及抑制蒸发功能随砂田退化程度的演变规律。【方法】基于多年Landsat卫星数据,使用辐射传输方程法反演香山地区砂田地表温度(LST),结合田间地表温度监测,对比砂田与裸地的地表温度变化,分析了砂田抑制土壤蒸发的机理,并探讨了砂田的功效与砂田使用年限的关系。【结果】砂田在LST-NDVI梯形空间中贴近于暖边,其土壤水分比耕地少,接近于干土层。因此,砂田可以隔离辐射与土壤表层,从而减小潜热通量,抑制土壤蒸发。砂田昼夜温差明显比裸地大,且对于西瓜等作物,砂田的有效地表积温也比裸地提高了10%。【结论】砂田退化过程可分为纯砾石阶段、砂土混合阶段和砂土连通阶段,从砂田的保温及抑制蒸发功能来看,砂田的有效使用年限为25～30 a。     

Mulch resistance to water vapor transport

Mulches augment soil moisture availability to plants by restraining direct evaporation of soil water. Yet, in field conditions wind decreases their resistance to water vapor transport, diminishing their efficiency as a water conservation measure. The relation between vapor transport resistance and wind speed was investigated in a wind tunnel where air flow was turbulent. The mulch material was chopped straw with bulk densities of 31 and 37 kg m⁻³, and chemically stabilized aggregates segregated in diameter classes 1-2, 2-4, 4-8, 8-11.2 mm, in layers 10-100 mm thick. The resistance decreased exponentially with increasing wind speed from the molecular diffusion value at zero wind speed, suggesting that turbulence penetrates the pores of the mulch and drives convective water vapor transport. Resistance rose exponentially with increasing layer thickness, a mirror reflection of the turbulence decay profile. Higher bulk density of the straw and finer aggregates augmented the resistance. The convective component of the vapor transport resistance was related to mulch area index, defined as the surface area of the solid elements of mulch per unit covered ground area. This procedure merged the effect of layer thickness and that of straw bulk density or aggregates size into a single function, indicating that friction forces proportional to internal area of the solid fabric restrain the penetration of momentum in the porous medium. Two-layered mulches combining straw and aggregates have a higher resistance than the sum of the resistances of the individual components as is expected from the attenuation of convection in the top layer. The functions derived in this study can serve as input for models evaluating the impact of mulches on soil water balance.     

Parameters affecting water vapor adsorption by the soil under semi-arid climatic conditions

Water vapor adsorption by the soil in Mediterranean ecosystems is very important to plant growth. We hypothesized that relative air humidity, soil texture, soil water content, and soil surface conditions affect water vapor adsorption. These factors were studied in four areas in Greece with semi-arid climatic conditions on four soils classified as Xerochrept. The study was conducted on hilly areas with various physiographic and microclimatic conditions greatly affecting daily fluctuations of air humidity. Time domain reflectometers (TDR) continuously monitored soil water content at depths 5, 10 and 25 cm. Rainfall, open pan water evaporation, air temperature, and relative air humidity were measured every 40 s, averaged, and recorded on data loggers every hour. Two weighing lysimeters were used to confirm soil water data measured by TDR-electrodes.The obtained data indicated that night-time water vapor adsorption is very important for areas characterized by high oscillation of air humidity (>25%), favored under certain physiographic and microclimatic conditions. Daily water vapor adsorption by the soil was inversely proportional related to the minimum air humidity, while adsorption increased proportionally as the daily amplitude of humidity increased. Cumulative water vapor adsorption decreased during the dry period as the amount of clay content increased. The depth of penetration of wetness increased as the amplitude of fluctuation in soil water content in the upper 5 cm soil layer increased. The presence of dense perennial shrubs growing in close contact with the soil surface greatly reduced water vapor adsorption by restricting the diurnal fluctuations in air humidity in the soil–atmosphere interface. Rock fragments or plant residues on the soil surface slightly reduced water vapor adsorption but greatly favored soil water conservation. The amount of water vapor adsorbed by the soil may satisfy up to 70% of the loss of water through evaporation during the dry period under semi-arid climatic conditions.     

盐渍土壤覆膜种植条件潜水蒸发的探讨与分析

盐渍土区潜水蒸发机理、特性及其计算方法的研究,对防治土壤盐碱化、地下水资源评价及农田水分管理具有重要意义.基于潜水蒸发的最新国内外研究成果,提出了当前在潜水蒸发研究方面的薄弱之处:即以往有关潜水蒸发的研究较多集中于其常规影响因素,且大多是对裸土条件下潜水蒸发特性及其计算进行研究,而对种植作物、土表覆膜和特殊土壤等条件下潜水蒸发问题的认识和研究较为不足.根据我国干旱地区土壤特性和种植模式,分别对有无作物种植、土表覆膜和盐渍土壤等3种条件下的潜水蒸发特性及计算方法进行了较为详细地阐述和评价,并就目前研究中存在的不足和未来亟待深入研究的问题进行了探讨,认为在今后的研究工作中,应把潜水蒸发对作物耗水的补给比例、不同地区适宜潜水埋深和生态地下水位、潜水蒸发昼夜变化特性,以及盐碱地潜水蒸发与土壤积盐的数值模拟等内容,作为研究重点.     

不同滴灌年限土壤盐分分布及对棉花的影响初步研究

随着膜下滴灌应用年限增加,农田土壤盐碱变化及对作物影响引起关注.通过在新疆石河子121团,选择地块相近连续应用膜下滴灌2～14 a棉田8块进行盐分变化监测.结果初步表明,膜内0～20 cm土壤脱盐;40～80 cm积盐;膜间裸地盐分表聚,60 cm以上积盐,100 cm以下与膜内土壤盐分接近.滴灌4 a以内盐分含量较高,滴灌6 a以上较低.生育期末0～40 cm土壤盐分随滴灌年限增加而降低;60～100 cm以滴灌4 a积盐最高.滴灌8 a以上棉花成活率较高、株高和单株铃数相差不大.棉花产量以滴灌8 a地块最高,滴灌8 a以内随滴灌年限增加产量增加,滴灌8 a以上随滴灌年限增加产量降低.建议滴灌6 a以内农田加大盐分调控力度,滴灌8 a以上要对土壤盐分进行综合调控.     

西北干旱区滴灌棉田膜间土壤蒸发试验研究

膜间土壤蒸发是覆膜棉田水分消耗的主要组成部分,在干旱少雨的新疆石河子利用微型蒸渗仪观测了地下滴灌和膜下滴灌条件下,覆膜棉田膜间土壤水分蒸发,并对膜间不同位置处的土壤蒸发规律进行了试验研究,研究结果表明,滴灌条件下膜间土壤水分蒸发分别与气温、辐射、饱和水汽差以及相对湿度呈指数相关关系,与参考作物需水量呈线型相关关系,与表层土壤含水率呈指数关系;膜间土壤累积蒸发量在苗期最高、其次是花铃期、吐絮期最小;膜下滴灌条件下膜边土壤的蒸发量高于膜间（两条膜正中间的裸地）蒸发量;地下滴灌条件下,错位种植会导致灌溉水的无效蒸发,不利于灌溉水的高效利用。     

不同位置秸秆覆盖条件下土壤水盐运动实验研究

以地下水与土壤水动力学理论为基础,通过对不同地下水埋深不同位置秸秆覆盖试验资料分析,建立了土壤水分运动数学模型,并进行了数值模拟,试验实测数据与模型计算值吻合较好,说明所建立的模型是可行的。并以此为基础,分析了不同地下水埋深不同位置秸秆覆盖土壤含盐量,得出地表以下30 cm处秸秆覆盖的土壤含盐量大于地表表层秸秆覆盖的土壤含盐量,这为新疆地区控制潜水蒸发改良盐碱地研究提供了可靠的基础依据。     

淮北平原汉王实验站土壤水资源特征试验研究

为了充分认识土壤水及其水资源特性,在淮北平原汉王水文水资源实验站对0.5～3.5 m地下水位控制条件下和秸秆、地膜、无覆盖三种条件下的土壤水分、包气带储水量、潜水蒸发、土壤蒸发、降雨入渗等要素进行了连续4年的观测,并结合水量平衡方程,对土壤水资源的要素特征进行了实验研究.结果表明：同一深度的土壤含水量大小顺序为秸秆覆盖〉地膜覆盖〉无覆盖;覆盖条件下土壤含水量变化相对稳定;土壤包气带有类似于土壤水库的作用,可调节水量可观,土壤水可作为一种重要的水资源;随土壤包气带厚度加大,潜水蒸发和降水下渗逐步减少,土壤蒸发表现突出.研究认为,充分认识土壤水资源特征,对指导土壤水资源开发利用、农业生产等有重要意义.     

秸秆覆盖对冬小麦耗水特征及水分生产率的影响

2季冬小麦试验结果表明 ,秸秆覆盖具有减少土壤棵间无效蒸发的作用 ,冬小麦返青前 1 m土层贮水量在砂壤土条件下秸秆覆盖处理比无覆盖处理增加 2 %～ 2 5 .8% ,粘壤土条件下增加 2 %～ 1 4.5 %。返青前秸秆覆盖处理比无覆盖处理的日耗水量普遍小 ,返青后情况则相反。秸秆覆盖能够促进作物生长 ,与无覆盖相比 ,提高水分生产效率 4.6%～ 2 5 .2 %。     

A simulation model of water dynamics in winter wheat field and its application in a semiarid region

Many models for water flow in cropped soil contain parameters such as rooting density, root permeability, and root water potential. Usually these parameters are chosen by trial-and-error method and direct measurements are difficult and impractical in some cases. This study presents a simulation model capable of analyzing water transport dynamics in a soil–plant–atmosphere continuum (SPAC). This model is developed by combining an existing mathematical model for soil water flow, a modified transpiration model taking into account of the air pressure and diurnal changes of the extinction coefficient of crop canopies, and a new simple model for root water uptake. Using data from lysimeters in a field experiment carried out on a wheat crop, we also developed two new empirical equations for the estimation of total canopy resistance and soil evaporation.We then applied the model for 2 years (1990–1991, 1991–1992) on winter wheat in a semiarid area of northwest China. Required parameters, particularly soil hydraulic and crop parameters, were determined by field and laboratory tests. Outputs from the simulation were in good agreement with the independent field measurements of seasonal changes in soil water content, canopy transpiration, surface evaporation, and root water uptake along the soil profile. In addition, this simulation agreed well with the actual measurements of seasonal crop water consumption and soil water balance among the treatments for different irrigation amounts.     

膜上灌春小麦调亏效应研究

在膜上灌水方式下覆膜和露地处理全生育期不同水分处理调亏下,膜上灌高产处理耗水量比对照减少了310.3mm却增产1363.69kg/hm2,同一水分处理下膜上灌丰水处理F(FM)比露地丰水处理F(B)增产40.99%,WUE提高了4.67kg/(mm.hm2);膜上灌中度处理M(FM)比露地中度处理M(B)增产52.55%,WUE提高了6.86kg/(mm.hm2)。相同水分条件下覆膜处理具有明显的增温、保墒增产作用,最高产量所需的土壤适宜水分下限较露地下降10%~15%。结果表明同一水分处理下覆膜小麦不仅具有较高的生物产量,而且具有较大的库容,因而开花后干物质积累量,茎、叶器官的输出率、分配率、转换率均高于露地小麦,最终表现为粒重增加经济产量提高。     

Hydraulic properties and water balance of a clay soil cropped with cotton

A field study was carried out in the Cukurova Region, Southern Turkey to investigate the magnitude of the components of water balance, and the water uptake by cotton roots in relation to hydraulic properties of a clay soil. A plot cropped with cotton and with bare soil only were equipped with tensiometers, gypsum blocks, and access tubes for neutron probe to monitor soil water potential and water content.The hydraulic conductivity values, evaporation and drainage rates, and water withdrawal of roots were determined from field data with numerical calculations based on water flow equations.Results showed that the evaporation from bare soil was generally high during the three month period May to July varying between 4.5 and 1.0 mm/day. However, when soil water potential at 10 cm depth had decreased to -0.065 and -0.070 MPa in the drying phase, the evaporation from the soil decreased to 0.4 mm/day. The drainage rates were influenced by rainfall.The highest values of capillary flux toward the surface layer, and drainage rate from the cropped soil, were 2.0 and 1.8 mm/day respectively. Rates of water uptake by roots from the soil profile, not including the 0–10 cm layer, were high when compared with drainage and upward fluxes, changing between 7.7 and 1.4 mm/day during the experimental period. A good agreement between root length densities and water uptake was found; up to 80% of all roots were in the top 50 cm of the soil and 78% of the total water uptake was extracted from the same layer. Evapotranspiration was found to decline as a cubic function of the available water content of the top 120 cm of the soil profile.     

覆膜开孔条件下斥水性层状土壤蒸发实验

覆膜开孔影响田间非均质土壤的水分运动过程,尤其当斥水程度不同时,其运动过程更趋于复杂.在控制土表不同覆膜开孔率条件下,进行了不同斥水程度的塿夹砂和砂夹塿的土柱蒸发实验,测定和分析了不同条件下土壤水分蒸发量变化过程和含水率剖面.结果表明,全覆膜的累积蒸发量-时间曲线明显较低,相应的蒸发10d后土壤水分剖面也与初始水分剖面接近,对于塿夹砂尤其明显.覆膜开孔率增加时,同条件下两种层状土的累积蒸发量与全覆膜相比均有明显增加,表明一旦覆膜开孔,覆膜保墒效应便明显降低.斥水程度增加时,累积蒸发量有所减小,说明斥水性的存在降低了水分运移速率.当土壤为严重斥水时,斥水性对水分运动过程的影响比覆膜开孔率的影响更明显.对于不同斥水程度的塿夹砂,采用对数函数表达累积蒸发量和时间的定量关系较好,而对于不同斥水程度下的砂夹塿分别采用幂函数和对数函数表达.     

地膜覆盖和秸秆覆盖春小麦棵间蒸发影响因素分析

对比分析了地膜覆盖和秸秆覆盖条件下春小麦棵间蒸发过程,以土壤热通量为大气因素,土壤温度、土壤水分为土壤因素,作物株高为作物因素,采用通径分析方法,研究了石羊河流域春小麦地膜覆盖和秸秆覆盖措施下影响棵间蒸发的因素。研究认为,土壤是影响春小麦棵间蒸发的主要因素。其中地膜覆盖条件下,土壤温度是影响棵间蒸发的重要因素和限制因素,秸秆覆盖条件下,减小土壤含水率将显著降低春小麦棵间蒸发量。     

An artificial capillary barrier to improve root zone conditions for horticultural crops: physical effects on water content

Capillary barriers (CBs) occur at the interface of two soil layers having distinct differences in textural and hydraulic characteristics. The objective of this study was to introduce an artificial CB, created by a layer of gravel below the root zone substrate, in order to optimize conditions for the cultivation of horticultural crops. Potential root zone formats were analyzed with and without the gravel CBs for variables including the following: depth of CB; barrier separating the root zone from the surrounding soil; and root zone soil texture. Field and simulated results revealed that artificial CBs increased root zone water content and changed water flow dynamics. Volumetric soil water content was increased by 20–70%, depending on the soil texture and depth of the barrier. Sandy soil texture and shallower placement resulted in relatively higher water content. For sandy soil without plants, a shallow (0.2 m depth) CB increased water content of the overlaying soil by 50% compared to the control. The introduction of a gravel CB below the root zone of pepper plants (Capsicum Annum L.) lead to 34% higher matric head, 50% lower diurnal fluctuations in matric head and 40% increase in pepper fruit yield. Increasing water content by way of artificial CBs appeared to improve the water use efficiency of pepper plants. Such an improvement could lead to reduced water and fertilizer application rates and subsequent reduction in contamination below the root zone. This is especially relevant for substrates of low water-holding capacity typically used in horticulture crop production.     

砾石覆盖条件下土壤水热效应对冬小麦田CO2排放的影响

通过2年田间试验,采用静态暗箱-气象色谱法监测冬小麦田CO_2排放速率和通量,并计算了生态系统净交换和收获指数。试验设置无覆盖对照(CK)、无覆盖补灌对照(WCK)、砾石覆盖(GM)和砾石覆盖补灌(WGM)4个处理。结果表明:2个生长季内砾石覆盖补灌处理各阶段土壤含水率和温度平均最高,其次为砾石覆盖处理,说明砾石覆盖的保水保温效果明显;土壤温度的变化规律与CO_2排放规律相同,土壤含水率变化规律与CO_2排放规律相反,土壤温度和含水率变化对CO_2排放具有显著的交互作用(P0.05);对影响农田生态系统CO_2排放的冬小麦生长参数和土壤理化特性进行相关矩阵和主成分分析,CO_2排放的分布与CK和WCK对照处理分布相似度较高,与GM和WGM砾石覆盖处理则完全相反;产量、收获指数、生态系统净交换的分布与WGM处理最为接近,其次为GM处理,说明砾石覆盖处理提高了产量,促进了生态系统净交换,降低了CO_2排放量。砾石覆盖结合关键生育期补充灌水的田间管理方式能有效改善土壤水热状况,减少农田生态系统CO_2排放。     

Sugarcane response to irrigation and straw mulch in a subtropical region

In Northern India, insufficient soil moisture and excessively high soil temperatures are reported to restrict growth of crops during the hot, dry months of April–June. A 3-year field experiment was conducted to evaluate the effects of three irrigation schedules based on ratios of 0.50, 0.75 and 1.00 times pan evaporation, and two levels of paddy straw mulch of 0 and 6 tons/ha on yield and quality of sugarcane for a sandy loam. The differential irrigations were restricted to 10–12 weeks before the monsoon season.Both irrigation and straw mulching had favourable effects on plant height and yield. Cane yield increased by an average of 13.8% for the 1.00 over the 0.50 times pan evaporation. Similarly, yield averaged 13.8% higher with mulch than without it. Interestingly, the pan evaporation ratio of 0.50 with mulch gave a higher yield than the ratio 1.00 without mulch. For the same yield, irrigation under mulching averaged 34 cm less than under no mulch. These beneficial effects were attributed to better soil moisture and temperature regimes with mulching. Irrigation and mulching had no effect on the quality of cane juice. These results indicate that straw mulching and early season irrigation to sugarcane based on 1.00 times pan evaporation is a promising practice for increasing sugarcane production in subtropical areas.     

地膜覆盖对土壤棵间蒸发影响的研究

农作物地膜覆盖栽培技术是 2 0世纪 80年代发展起来的新技术 ,其保温、保墒和增产效果明显 ,但不同地膜覆盖率对减少土壤棵间蒸发影响规律 ,目前国内研究不多。通过在室内研究覆膜灌溉土壤蒸发规律 ,研究出不同土壤含水率的水分蒸发和不同覆盖率对土壤蒸发的影响关系 ,并在田间进行验证。为今后定量评价农作物地膜覆盖减少土壤棵间蒸发提供理论依据     

Effects of rainfall harvesting and mulching technologies on water use efficiency and crop yield in the semi-arid Loess Plateau, China

In semi-arid areas, crop growth is greatly limited by water. Amount of available water in soil can be increased by surface mulching and other soil management practices. Field experiments were conducted in 2005 and 2006 at Gaolan, Gansu, China, to determine the influence of ridge and furrow rainfall harvesting system (RFRHS), surface mulching and supplementary irrigation (SI) in various combinations on rainwater harvesting, amount of moisture in soil, water use efficiency (WUE), biomass yield of sweet sorghum (Sorghum bicolour L.) and seed yield of maize (Zea mays L.). In conventional fields without RFRHS, gravel-sand mulching produced higher biomass yield than plastic-mulching or straw-mulching. In plastic-mulched fields, an increasing amount of supplemental irrigation was needed to improve crop yield. There was no effect of RFRHS without plastic-covered ridge on rainwater harvesting when natural precipitation was less than 5 mm per event. This was due to little runoff of rainwater from frequent low precipitation showers, and most of the harvested rainwater gathered at the soil surface is lost to evaporation. In the RFRHS, crop yield and WUE were higher with plastic-covered ridges than bare ridges, and also higher with gravel-sand-mulched furrows than bare furrows in most cases, or straw-mulched furrows in some cases. This was most likely due to decreased evaporation with plastic or gravel-sand mulch. In the RFRHS with plastic-covered ridges and gravel-sand-mulched furrows, application of 30 mm supplemental irrigation produced the highest yield and WUE for sweet sorghum and maize in most cases. In conclusion, the findings suggested the integrated use of RFRHS, mulching and supplementary irrigation to improve rainwater availability for high sustainable crop yield. However, the high additional costs of supplemental irrigation and construction of RFRHS for rainwater harvesting need to be considered before using these practices on a commercial scale.     

干旱区大田膜下滴灌对土壤盐分的影响

为研究干旱区大田膜下滴灌土壤盐分运移特征,在新疆石河子炮台试验站进行连续4年的试验研究。结果表明,膜下滴灌条件下,边行盐分偏高,棵间土壤盐分上升;耕作层土壤盐分下降,耕作层以下则增加,但由于滴灌灌水频繁,作物根系分布层内(0～40cm)土壤盐分始终处于较低值;利用膜下滴灌可以明显降低盐荒地土壤盐分,加速盐荒地改良和弃耕地的收复。