In situ water transmission characteristics of a tropical soil under rice-based cropping systems

In soils under rice-based cropping systems in Asia water movement and distribution in the root zone of rice and dryland crops are important for efficient water management. Saturated hydraulic conductivities in the wetland soil profile were evaluated from measurements of hydraulic gradients and percolation rates in the field. The subsoil layer (15–60 cm) restricted percolation rate to a greater degree than the puddled top soil.Unsaturated hydraulic conductivities and soil water diffusivities in the soil profile under dryland conditions were obtained from simultaneous measurements of soil water content using the neutron moderation technique and the soil matric potential by tensiometers over time and soil depth. Soil matric potential versus hydraulic conductivity and soil water content versus soil water diffusivity relations of various soil depths were established. At equivalent soil matric potentials, the hydraulic conductivity of surface soil was greater than that of the subsoil layers. Soil water diffusivity at different depths responded similarly. The study describes a simple in situ technique to measure percolation rates in wetland rice fields and evaluation of water transmission properties of field soil profiles.     

振动深松耕作对不同类型土壤水分特征曲线影响研究

为了探讨振动深松耕作措施对不同类型土壤的水分特征曲线的影响,利用吸力平板仪和压力膜仪对黑龙江省5种典型土壤,即黑土、黑钙土、水稻土、苏打盐碱土、沙土进行了测定。得到振动深松区和对照区的原状土壤在脱湿过程中不同吸力下的土壤含水率,并利用van Genuchten数学模型对5种土壤的水分特征曲线的实测值进行数值拟合,对比研究了5种土壤水分特征曲线及模型拟合参数、土壤当量孔径、土壤水分有效性及比水容量的变化。结果表明,振动深松前后土壤水分特征曲线差异显著。同一吸力下,深松区土壤含水率高于对照区,振动深松显著提高了土壤的有效供水能力,其中效果最佳的是苏打盐碱土和黑土。振动深松通过改善土壤结构,调整了孔隙孔径的比例,进而提高了土体的有效供水能力。     

Soil surface shrinkage to estimate profile soil water

Summary The surface elevation of a shrinking soil provided good estimates of the change in profile water content under alfalfa. Surface shrinkage was found to change linearly with water content as measured by neutron and gamma attenuation devices. Extracted soil cores were tested in the laboratory to obtain the linear shrinkage ratio, b. In the field, shrinkage was calculated as the average elevation change of small ceramic plates. Compaction of the soil by harvesting machinery had no adverse effect on the linearity of the shrinkage/water loss relationship, but lack of compaction resulted in nonlinear shrinkage as the soil was unconsolidated and may have exhibited sub-surface horizontal cracking. These cracks were attributed to roots which anchored the soil during shrinkage. In a second study, local values of swelling (b) from initial measurements before and after irrigation were superior estimators of measured water loss compared to a single universal b value from independent tests.     

Field calibration of a neutron moisture meter in a cracking grey clay

Summary A neutron moisture meter was field calibrated in a cracking grey clay prepared for furrow irrigation at Narrabri, N.S.W. Neutron counts were taken in successive 0.1 m increments between the 0 and 1.5 m depths. Concomitant measurements using undisturbed soil cores provided independent estimates of volumetric water content. Separate linear calibrations were required for the 0–0.1 m, 0.1–0.2 m and 0.2–1.5 m depth increments. Correction for bias due to cracking and changes in bulk density slightly improved the calibrations. The accuracy of predicted soil water content was improved relative to previous calibrations. A precision of ±0.01 m³m^–3 required 3 samples per mean by the neutron method or 11 samples per mean by the core sampling method.     

Application of time-domain reflectometry (TDR) soil moisture miniprobe for the determination of unsaturated soil water characteristics from undisturbed soil cores

Summary Construction and operating characteristics of a TDR soil moisture miniprobe, that can be inserted through the wall of a metal cylinder, are shown. A laboratory stand for monitoring unsaturated water flow in undisturbed soil cores, involving a set of TDR miniprobes in combination with a set of minitensiometers, is described. This stand was used for frequent readings of instantaneous profiles of moisture and matric potential during transition from saturated to air dry state, in order to compute the unsaturated soil water characteristics. Some methodical aspects of the applied data processing algorithm are outlined.     

土壤基质势调控对温室滴灌番茄土壤水分分布和产量的影响

【目的】指导设施蔬菜生产中科学合理地利用滴灌技术进行灌溉。【方法】采用小区试验的方法,以冬春茬番茄为研究对象,布置了7个不同土壤基质势阈值的试验,在番茄开花坐果期和结果期分别控制滴头正下方20 cm深度土壤基质势在-15和-15 kPa(S1)、-15和-30 kPa(S2)、-15和-45 kPa(S3)、-25和-25 kPa(S4)、-30和-15 kPa(S5)、-30和-30 kPa(S6)以及-30和-45 kPa(S7),研究了日光温室滴灌土壤基质势调控下土壤水分随时间变化及空间分布的规律,以及番茄产量、畸形果率和灌溉水利用效率等。【结果】①控制滴头正下方20 cm深度土壤基质势可以明显影响0～100 cm深度土壤水分状况。②在番茄开花坐果期,当土壤基质势阈值控制在-30 kPa或更高时,番茄根系主要吸收利用0～60 cm深度以上范围的土壤水分,70 cm深度以下土壤水分基本不变,0～60 cm深度土壤体积含水率平均为28.6%,为田间持水率的84%,60～100 cm土壤体积含水率平均为36.2%,为田间持水率的90%。③番茄进入结果期后,当土壤基质势阈值控制在-25～-15 kPa时,整个土体土壤含水率基本保持在田间持水率的77%～91%,根系主要吸收利用0～60 cm深度以上范围的土壤水分,70 cm深度以下土壤水分消耗缓慢;当土壤基质势阈值降低到-45～-30 kPa时,根系吸收利用到80～100 cm深度的土壤水分,整个土体土壤含水率不断降低,降低到田间持水率的60%～66%。④不同处理番茄产量、畸形果率和灌溉水利用效率有明显差异,其中S3和S7处理番茄产量高,S5处理产量低;S1、S3和S4处理的畸形果率大,S6和S7处理的畸形果率低;S1处理的灌溉水利用效率最低,S7处理的灌溉水利用效率最高。【结论】日光温室少量高频滴灌条件下,当滴头正下方20 cm深度土壤基质势阈值开花坐果期控制在-30 kPa、结果期控制在-45 kPa时,整个土体土壤水分状况基本良好,番茄的产量高,畸形果率低,灌溉水利用效率高。     

沙地喷灌土壤基质势调控对土壤水分分布和马铃薯产量的影响

[目的]制定砂质土壤马铃薯的喷灌灌溉制度。[方法]选择“夏波蒂”(抗旱性弱)和“费乌瑞它”(抗旱性强)2种不同抗旱能力的马铃薯品种,通过2a的田间试验,研究了不同土壤基质势阈值对土壤水分状况、马铃薯产量与灌溉水利用效率等的影响,以确定马铃薯适宜的土壤基质势阈值来指导灌溉。2012年布置了3个处理,在马铃薯定苗后分别控制垄中心20cm深度处土壤基质势阈值为-20、-30和-40kPa,2013年增加了1个-10kPa处理。[结果]大型喷灌机灌溉条件下监控垄中心20cm深度处土壤基质势可较好地调控马铃薯农田的土壤水分状况;①指导灌溉的土壤基质势阈值越高,马铃薯生育期内0~30cm深度平均土壤基质势越高,并且变化幅度越平缓;土壤基质势阈值越低,0~30cm深度平均土壤基质势越低,且变化越剧烈;40cm深度以下土壤水分状况与土壤基质势阈值的关系不明显。②不同抗旱能力马铃薯品种的产量都随着土壤基质势阈值的降低而线性降低,当阈值低于-15.8 kPa时,土壤基质势每降低1kPa,产量降低1.8%,且主要表现在大薯(W≥250g)和中薯(150g≤ W<250g)质量的降低,单株结薯个数基本不受影响。③灌溉水利用效率随着土壤基质势的降低而线性增加,表现为土壤基质势每降低1 kPa,灌溉水利用效率升高1.3%。[结论]砂质土壤大型喷灌机灌溉或类似农业生产条件下,推荐监控垄中心20cm深度处土壤基质势来指导施肥灌溉,并且土壤基质势阈值建议为-15.8 kPa左右,在淀粉积累期之后可考虑适当地降低土壤基质势阈值,以获得高产和较高的灌溉水利用效率。     

日光温室滴灌条件下土壤基质势对彩椒生长的影响

利用埋在滴头正下方0.2 m深度的真空表负压计,通过控制土壤基质势下限(-10 kPa,S1;-20 kPa,S2;-30 kPa,S3;-40 kPa,S4),研究太行山山前平原日光温室覆膜滴灌条件下土壤基质势对秋冬茬彩椒(紫星二号)(Capsicum frutescens L.)生长的影响。试验结果表明,彩椒的株高和叶面积随土壤基质势的提高而增加;但过高的土壤基质势导致彩椒产量下降,土壤基质势在-30 kPa时,彩椒产量和灌溉水利用效率最高;彩椒果实的可溶性糖和可溶性固形物含量随土壤基质势的提高而降低;彩椒果实的Vc含量和土壤基质势的变化梯度没有关系。综合考虑彩椒产量、品质和灌溉水利用效率,日光温室覆膜滴灌条件下彩椒的土壤基质势控制在-20~-30 kPa最为适宜。     

Soil matric potential-based irrigation scheduling to rice (Oryza sativa)

About half of the total fresh water used for irrigation in Asia is used for rice production. Decreasing water resources and increasing water costs necessitates increasing water use efficiency for rice. The most common method of irrigation in northwestern India is through alternate wetting and drying with a fixed irrigation interval, irrespective of soil type and climatic demand resulting in over-irrigation or under-irrigation under different soil and weather situations. Soil matric potential may be an ideal criterion for irrigation, since variable atmospheric evaporativity, soil texture, cultural practices and water management affect rice irrigation water requirements. A 4-year field study was conducted to assess the feasibility of rice irrigation scheduling on the basis of soil matric potential and to determine the optimum matric potential so as to optimize irrigation water without any adverse effect on the yield. The treatments included scheduling irrigation to rice with tensiometers installed at 15–20 cm soil depth at five levels of soil matric suction viz. 80, 120, 160, 200 and 240±20 cm, in addition to the recommended practice of alternate wetting and drying with an interval of 2 days after complete infiltration of ponded water. The grain yield of rice remained unaffected up to soil moisture suction of 160±20 cm each year. Increasing soil matric suction to 200 and 240±20 cm decreased rice grain yield non-significantly by 0–7% and 2–15%, respectively, over different years compared to the recommended practice of the 2-day interval for scheduling irrigation. Irrigation at 160±20 cm soil matric suction helped save 30–35% irrigation water compared to that used with the 2-day interval irrigation. With a soil matric potential irrigation criterion the total amount of irrigation water used was a function of the number of rainy days and evaporation during the rice season.     

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.     

An artificial capillary barrier to improve root-zone conditions for horticultural crops: response of pepper, lettuce, melon, and tomato

Capillary barriers (CBs) occur at the interface between two soil layers having distinct differences in hydraulic characteristics. In preliminary work without growing crops, it was demonstrated that CBs implemented in sandy soils increased hydrostatic volumetric water content by 20–70%, depending on soil texture and depth of barrier insertion. We hypothesized that the introduction of an artificial CB at the lower root-zone boundary of horticultural crops can increase yields as a result of increased water content and uptake efficiency. The effects of introduced CBs on soil water content, plant growth, and yields of bell peppers (Capsicum annum L), lettuce (Lactuca sativa L), tomatoes (Lycopersicon esculantum L.), and melons (Cucumis melo L.) were studied in a desert environment in southern Israel. Inclusion of a CB increased soil water content by 60% and biomass and fruit yields by 25% for pepper, and increased matric head and biomass yield by 80 and 36%, respectively, for lettuce. Neither tomatoes nor melons reacted significantly to the presence of CBs, in spite of increased soil moisture. Daily soil matric head amplitude was reduced fivefold when lettuce was grown with a CB. Spatial variability was highly reduced when a CB was present. When peppers were grown with a CB, the standard deviations of water content and biomass yield were reduced by 40% relative to control.     

基于土壤基质势的灌溉预报及自动控制系统设计

为了使灌溉预报及自动控制系统简单、投资成本低且便于推广应用,设计了一套基于土壤基质势的灌溉预报及自动控制系统.通过利用电接点压力表测量负压计中的压力,设定不同作物、不同生育期、不同灌水方式的灌水下限和上限.当土壤基质势达到灌水上下限时,通过电接点压力表和自动控制电路,实现灌溉预报和自动控制.灌水过程中,通过单片机、远传水表和液晶显示屏,可以实现灌水时间、灌水量和灌水次数的记录与存储.经室内试验验证表明基于土壤基质势的灌溉预报及自动控制系统合理可行,对于粉砂壤土可以将灌水上限的土壤基质势设置为-8 kPa左右.     

Growth and yield of oleic sunflower (Helianthus annuus L.) under drip irrigation in very strongly saline soils

A four-year trial was set up to test the feasibility of growing oleic sunflower in a very strongly saline wasteland with drip irrigation in the Ningxia plain of Northwest China. The soil salinity expressed as electrical conductivity of the saturation paste extract (EC _e ) was around 28 dS/m, and soil nutrient was deficient in the upper 120 cm depth. The experiment included five soil matric potential (SMP) treatments, with the SMP at 20-cm depth immediately under the emitters maintained to be higher than ?5, ?10, ?15, ?20 and ?25 kPa after sunflower establishment. Drip irrigation consistently created a favourable soil moisture and low-salinity region in the root zone when the SMP was maintained higher than ?25 kPa. The sunflower dry seed yield decreased by 3.8 % for each unit increase in seasonal average soil salinity in the root zone. Plant vegetative growth, yield characteristics, irrigation frequency and irrigation amount all increased with the increase in SMP from ?25 to ?5 kPa, and the highest irrigation water use efficiency was available when the SMP was between ?10 and ?15 kPa (the amount of applied water was around 750 mm). Leaching of salts by drip irrigation gradually turned the very strongly saline soil into a moderately saline soil. This research suggests that drip irrigation can be successfully used in oleic sunflower cultivation in this highly saline soil and a SMP threshold between ?10 and ?15 kPa is suggested for irrigation scheduling.     

Potato evapotranspiration and yield under different drip irrigation regimes

A field experiment comparing different irrigation frequencies and soil matric potential thresholds on potato evapotranspiration (ET), yield (Y) and water-use efficiency (WUE) was carried out in a loam soil. The experiment included five treatments for soil matric potential: F1 (-15 kPa), F2 (-25 kPa), F3 (-35 kPa), F4 (-45 kPa) and F5 (-55 kPa) and six treatments for irrigation frequency: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days). Results indicate that both soil matric potential and drip irrigation frequency influenced potato ET, Y and WUE. Potato ET increased as irrigation frequency and soil matric potential increased. Comparing soil water potential, the highest ET was 63.4 mm (32.1%) more than the lowest value. Based on irrigation frequency treatments, the highest ET was 36.7 mm (19.2%) more than the lowest value. Potato Y and WUE were also found to increase as irrigation frequency increased. Potato Y increased with an increase in soil water potential then started to decrease. The highest Y and WUE values were achieved with a soil matric potential threshold of -25 kPa and an irrigation frequency of once a day.Communicated by J. Ayars     

滴灌条件下土壤基质势对豇豆产量和灌溉水利用效率的影响

研究了华北半湿润区滴灌条件下不同土壤基质势对露地栽培豇豆产量和灌溉水利用效率的影响。试验共有5个处理,分别控制滴头正下方0.2 m深度处土壤基质势下限高于-10、-20、-30、-40和-50 kPa。研究分析发现,土壤基质势对豇豆的产量没有明显的影响,并且随着土壤基质势控制的降低,豇豆整个生育期的灌水量明显降低,灌溉水利用效率显著升高。因此,在华北半湿润区,在保证豇豆安全度过苗期之后,可以通过控制滴头正下方0.2 m深度处土壤基质势下限高于-50 kPa来制定豇豆的滴灌灌溉计划。     

沙地大型喷灌机施肥灌溉配套鱼鳞坑对马铃薯生长和水肥利用的影响研究

为了实现沙地上大型喷灌机施肥灌溉下马铃薯的水肥高效利用,通过田间试验研究了大型喷灌机施肥灌溉条件下配套水土保持措施——鱼鳞坑对马铃薯生长、水肥利用效率等的影响。结果表明,在大型喷灌机条件下,通过负压计指导施肥灌溉,当垄中心20cm深度处的土壤水基质势低于-15kPa时进行施肥灌溉时,在马铃薯垄间挖鱼鳞坑,能有效地改善根区土壤水分状况,促进马铃薯的生长,不仅马铃薯增产22.1%~33.3%,还使肥料偏生产力提高了33.3%~36.8%。     

Simulation of putting-green soil water dynamics: Implications for turfgrass water use

Results from a field experiment examining soil water fate within U.S. Golf Association (USGA) putting greens were used to examine the validity of a water flow simulation model. The experiment used six different sandy root zones each with depths of 300 mm overlying a 100 mm thick gravel layer. Data collected over two growing seasons consisted of measured rainfall, irrigation, drainage volume, and soil water contents; and calculated turfgrass evapotranspiration (ET). Turfgrass rooting was measured at the end of each growing season, and water retention curve and saturated hydraulic conductivity measurements were conducted at the end of the study. For each root zone treatment, HYDRUS-2D (H2D) was calibrated using a subset of the experimental data and then validated by comparing observed and predicted water contents at 76, 152 and 229 mm depth and over both growing seasons. Model efficiency (E) ranged from 0.33 to 0.78; Mean Absolute Error (MAE) ranged from 0.012 to 0.024 m³ m⁻³; and Root Mean Square Error (RMSE) ranged from 0.015 to 0.028 m³ m⁻³, for the six treatments and both years. Also, RMSE values were at best slightly larger than and at worst twice as large as the mean standard deviation values of replicate measurements. Thus, H2D simulation performed reasonably well in describing the water content results of the field study. The calibration results provide evidence of hysteresis in water retention where water retention properties from the field appear to follow the sorption or wetting curve as compared with the laboratory measurements following the desorption or drying curve. This suggests that standard laboratory measurements of water release would not precisely predict water retention behavior in the field and over estimate water storage of these capillary barrier soils. The validation results provide evidence for turfgrass use of perched water held within these profiles, even though turfgrass rooting is shallow and water storage principally occurs deep within the root zone. Thus, the perched water of USGA putting greens should serve reasonably well as a water reservoir for subsequent turfgrass use, allowing for water conserving irrigation practices that makes use of this stored water.     

Modelling soil water and salt dynamics under pulsed and continuous surface drip irrigation of almond and implications of system design

The HYDRUS-2D model was experimentally verified for water and salinity distribution during the profile establishment stage (33?days) of almond under pulsed and continuous drip irrigation. The model simulated values of water content obtained at different lateral distances (0, 20, 40, 60, 100?cm) from a dripper at 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140 and 160?cm soil depths at different times (5, 12, 19, 26 and 33?days of profile establishment) were compared with neutron probe measured values under both irrigation scenarios. The model closely predicted water content distribution at all distances, times and soil depths as RMSE values ranged between 0.017 and 0.049. The measured mean soil water salinity (ECsw) at 25?cm from the dripper at 30, 60, 90 and 150?cm soil depth also matched well with the predicted values. A correlation of 0.97 in pulsed and 0.98 in continuous drip systems with measured values indicated the model closely predicted total salts in the root zone. Thus, HYDRUS-2D successfully simulated the change in soil water content and soil water salinity in both the wetting pattern and in the flow domain. The initial mean ECsw below the dripper in pulsed (5.25?dSm^?1) and continuous (6.07?dSm^?1) irrigations decreased to 1.31 and 1.36?dSm^?1, respectively, showing a respective 75.1 and 77.6% decrease in the initial salinity. The power function [y?=?ax ^?b ] best described the mathematical relationship between salt removal from the soil profile as a function of irrigation time under both irrigation scenarios. Contrary to other studies, higher leaching fraction (6.4–43.1%) was recorded in pulsed than continuous (1.1–35.1%) irrigation with the same amount of applied water which was brought about by the variation in initial soil water content and time of irrigation application. It was pertinent to note that a small (0.012) increase in mean antecedent water content (θ _i ) brought about 8.25–9.06% increase in the leaching fraction during the profile establishment irrespective of the emitter geometry, discharge rate, and irrigation scenario. Under similar θ _i , water applied at a higher discharge rate (3.876?Lh^?1) has resulted in slightly higher leaching fraction than at a low discharge rate (1.91?Lh^?1) under pulsing only owing to the variation in time of irrigation application. The influence of pulsing on soil water content, salinity distribution, and drainage flux vanished completely when irrigation was applied daily on the basis of crop evapotranspiration (ETc) with a suitable leaching fraction. Therefore, antecedent soil water content and scheduling or duration of water application play a significant role in the design of drip irrigation systems for light textured soils. These factors are the major driving force to move water and solutes within the soil profile and may influence the off-site impacts such as drainage flux and pollution of the groundwater.     

基于土壤水力传导度自动测试系统的瞬时剖面法试验应用

水力传导度表征土壤对水分流动的传导能力,是计算土壤水分运动的一个重要参数,反映非饱和土壤的导水率随含水率或基质势的变化关系。该文采用TS-4型土壤水力传导度测试系统分别对两种土壤进行了3次试验,结果表明:自动测定系统具有方便快捷、精度较高的特性,为实验室模拟非饱和土壤水运动参数测定试验提供了一种有效的方法。      

质地和根系深度对水分探头埋设的仿真模拟

利用Hydrus-1D模型模拟不同植物根系深度和不同土壤质地条件下的土壤水分动态与平衡,研究了根系分布深度和质地对控制灌溉土壤水分探头埋设深度的影响,并利用试验进行了验证. 土壤质地和植物根系分布深度对探头埋设深度有显著影响,砂壤土和壤土分别采用高频低灌量和低频率高灌量的方法.浅根系植物（10 cm）在砂壤土条件下探头埋设5 cm深度最佳,但是根系深度增大到30 cm,探头应该埋设到20 cm深度.对壤土而言,利用位于根系1/2至1/3处的探头控制灌溉. 太浅的埋设深度会导致灌溉频率增大,太深的埋设可能造成植物缺水.黏土条件下,结果较为复杂,探头的埋设深度需要田间试验研究. 研究结果表明：针对具体植物,因其需水规律和生理特征的不同,根据植物需水规律来调整探头的控制范围达到高效节水目的.