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.     

Cotton response to short-term waterlogging imposed with a water-table gradient facility

Waterlogging of field-grown plants can occur either when the surface of slowly permeable soils is inundated or when the water-table rises so that part or all of the root zone is saturated. The effects of short-term waterlogging on field crop growth and yield have not been well quantified. To study these effects, a sloping, repacked slab of soil underlain by an impermeable membrane was constructed. The sloping plot (45 m long × 6 m wide × 0.6 m deep) was flooded by introducing water through a drainage network and gravel bed so that a gradient of water-table depth ranging from 0.1 m above to 0.66 m below the soil surface was obtained. Cotton (Gossypium hirsutum cv. Deltapine 61) was grown in the facility and the responses of plants to two periods of flooding were monitored. Soil matric potential and oxygen partial pressure data indicated that plants were subjected to a continuum of conditions ranging from complete inundation to no water-table within the root zone.The first flooding event began 82 days after sowing just prior to the main flowering period. Plants with more than 55% of their root system below the water table showed decreased leaf growth about 3–4 days after the flooding started with visible wilt symptoms and decreased leaf water potential observed on days 7 and 8 of flooding. In the second flooding event (131 days after sowing), plants showed no signs of waterlogging stress apart from reduced leaf growth despite 16 days of flooding. Plant growth response was probably more the result of reduced nutrient status (mostly nitrate) rather than a water deficit stress effect with some plant acclimatization between the first and second flooding event. Seed cotton yield data indicated that the observed stress during the first flooding event may have promoted reproductive growth in plants where the short-term water-table was greater than 0.2 m below the soil surface.     

盐碱地滴灌对新疆杨生长及土壤盐分分布影响

通过田间试验研究高垄覆膜滴灌模式下不同土壤基质势对盐碱地新疆杨生长以及土壤盐分分布的影响。试验设5个水平的土壤基质势处理：-5kPa（S1）,-10kPa（S2）,-15kPa（S3）,-20kPa（S4）,-25kPa（S5）,每个处理重复3次,按随机区组布置。试验结果表明,2009年生育末期,根系周围土体中的盐分比...     

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。     

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.     

The response of sap flow in apple roots to localised irrigation

The oft-touted reason for the efficiency of drip irrigation is that roots can preferentially take up water from localised zones of water availability. Here we provide definitive evidence of this phenomenon. The heat-pulse technique was used to monitor rates of sap flow in the stem and in two large surface roots of a 14 year old apple tree (Malus domestica Borkh. cv. Braeburn). The aim was to determine the ability of an apple tree to modify its pattern of root water uptake in response to local changes in soil water content. We monitored the water status of the soil close to the instrumented roots by using time domain reflectometry (TDR) to measure the soil's volumetric water content, θ, and by using ceramic-tipped tensiometers to measure the soil's matric pressure head, h. A variation in soil water content surrounding the two roots was achieved by supplying a single localised irrigation to just one root, while the other root remained unwatered. Sap flow in the wetted root increased straight away by 50% following this drip irrigation which wetted the soil over a zone of approximately 0.6 m in diameter and 0.25 m in depth. Sap flow in the wetted root remained elevated for a period of about 10 days, that is until most of the irrigation water had been consumed. A comparative study of localised and uniform irrigation was then made. Following irrigation over the full root zone no further change in sap flow in the previously wetted root was observed when referenced to the corresponding sap flow measured in the stem of the apple tree. However sap flow in the previously dry root responded to subsequent irrigations by increasing its flow rate by almost 50%. These results show that apple roots have the capacity to transfer water from local wet areas at much higher rates than normally occurs when the entire root zone is supplied with water. They are also able to shift rapidly their pattern of uptake and begin to extract water preferentially from those regions where it is more freely available. Such an ability supports the use of drip irrigation for the efficient use of scarce water resources. We conclude that the soil-to-root pathway represents a major resistance to water uptake by apple, even at the relatively high soil water pressure heads developed during parts of this experiment, during which the tree was not even under any stress.     

Model for assessing impact of salinity on soil water availability and crop yield

The salinity condition in the root zone hinders moisture extraction from soil by plants, because of osmotic potential development in soil water due to presence of salts, which ultimately, decreases transpiration of plants and thereby affects crop yield. Therefore, an effort was made in this study to quantify the impact of salinity on soil water availability to plants. The movement of salts under irrigation and evapotranspiration regimes in root zone of soil profile was studied throughout the growing season of wheat crop with adopting exponential pattern of root water uptake. A model was developed to analyze soil water balance to find out moisture deficit because of salinity. A non-linear relationship was formulated between moisture content and salt concentration for simultaneous prediction. The Crank–Nicolson method of Finite Differencing was used to solve the differential equations of soil water and solute transport. The effect of various salt concentrations on transpiration was analyzed to develop a relationship between relative evapotranspiration and relative yield. Relationships among salt concentration, matric potential, moisture deficit and actual transpiration were also established to provide better understanding about impact of salinization and to provide guidelines for obtaining better crop yields in saline soils.     

Salt distribution and the growth of cotton under different drip irrigation regimes in a saline area

A 3-year experiment was conducted in an extremely dry and saline wasteland to investigate the effects of the drip irrigation on salt distributions and the growth of cotton under different irrigation regimes in Xinjiang, Northwest China. The experiment included five treatments in which the soil matric potential (SMP) at 20 cm depth was controlled at −5, −10, −15, −20, and −25 kPa after cotton was established. The results indicated that a favorable low salinity zone existed in the root zone throughout the growing season when the SMP threshold was controlled below −25 kPa. When the SMP value decreased, the electrical conductivity of the saturation paste extract (EC_e) in the root zone after the growing season decreased as well. After the 3-year experiment, the seed-cotton yield had reached 84% of the average yield level for non-saline soil in the study region and the emergence rate was 78.1% when the SMP target value was controlled below −5 kPa. The average pH of the soil decreased slightly after 3 years of cultivation. The highest irrigation water use efficiency (IWUE) values were recorded when the SMP was around −20 kPa. After years of reclamation and utilization, the saline soil gradually changed to a moderately saline soil. The SMP of −5 kPa at a depth of 20 cm immediately under a drip emitter can be used as an indicator for cotton drip irrigation scheduling in saline areas in Xinjiang, Northwest China.     

Validation of a root water uptake model to estimate transpiration constraints

Experimental results obtained from a greenhouse trial with common bean (Phaseolus vulgaris L.) plants performed to test model hypotheses regarding the onset of limiting hydraulic conditions and the shape of the transpiration reduction curve in the falling rate phase are presented. According to these hypotheses based on simulations with an upscaled single-root model, the matric flux potential at the onset of limiting hydraulic conditions is as a function of root length density and potential transpiration rate, while the relative transpiration in the falling rate phase equals the relative matric flux potential. Transpiration of bean plants in water stressed pots with four different soils was determined daily by weighing and compared to values obtained from non-stressed pots. This procedure allowed determining the onset of the falling rate phase and corresponding soil hydraulic conditions. At the onset of the falling rate phase, the value of matric flux potential M_l showed to differ in order of magnitude from the model predicted value for three out of four soils. This difference between model and experiment can be explained by the heterogeneity of the root distribution which is not considered by the model. An empirical factor to deal with this heterogeneity should be included in the model to improve predictions. Comparing the predictions of relative transpiration in the falling rate phase using a linear shape with water content, pressure head or matric flux potential, the matric flux potential based reduction function, in agreement with the hypothesis, showed the best performance, while the pressure head based equation resulted in the highest deviations between observed and predicted values of relative transpiration rates.     

Water and salt regulation and its effects on Leymus chinensis growth under drip irrigation in saline-sodic soils of the Songnen Plain

Field experiments were carried out to investigate water and salt management and its effects on Leymus chinensis growth under drip irrigation on saline-sodic soils of the Songnen Plain, China. The ECe of the experiment soil here is 15.2 dS/m and SAR_e is 14.6 (mmol_c L⁻¹)^1/2. The threshold of soil matric potential (SMP) was preset in different treatments (−5, −10, −15, −20 and −25 kPa) to control the timing of the irrigation cycle using vacuum tensiometers buried at 0.2 m depth immediately under drip emitters. Drip irrigation frequency and soil matric potential significantly influenced water and salt distributions and L. chinensis growth. In the root zone, the soil water content increased with the SMP, but at deeper layers there were no significant differences in soil water content due to the effect of groundwater. Electrical conductivity showed that there was a low-salt zone near the emitters and that drip irrigation inhibited the buildup of salts in the root zone. There was more leaching of salts for −5 and −10 kPa treatments than for the −15, −20 and −25 kPa treatments. After two years of drip irrigation, the surface salts were well leached, and had moved down with the water to depths below 40 cm. The pH of each treatment was a little decreased and the soil nutrient of S1-S5 were all increased after reclamation, but there were no obvious differences of the five treatments. The best growth was achieved with soil matric potentials of −5 and −10 kPa: the plant height, number and length of spikes, number of tillers, coverage and aboveground biomass all attained their maximum values during the growth periods of L. chinensis, with no significant differences between those two treatments. Thus, in the Songnen Plain, drip irrigation can be used on transplanted L. chinensis for restoration of saline-sodic soils. The results provide theoretical and technological guidance for sustainable reclamation salt-affected soil and the quick restoration and reconstruction of saline-sodic grassland.     

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.     

Evaluation of capacitance probes for optimal irrigation of citrus through soil moisture monitoring in an entisol profile

 Continuous monitoring of soil moisture content within and below the rooting zone can facilitate optimal irrigation scheduling aimed at minimizing both the effects of water stress on the plants, and also the leaching of water below the root zone, which can have adverse environmental effects. The use of Sentek capacitance probes (EnviroSCAN RT5) in scheduling citrus irrigation was evaluated using 3-year-old Hamlin orange trees [Citrus sinensis (L.) Osb.] on Swingle citrumelo rootstock [Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf.] grown in a Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments). Available soil moisture calculated according to capacitance probe readings of soil moisture agreed well with that calculated using soil water release curves determined in the laboratory. A utility program was developed to process the data collected by the capacitance probe into a spreadsheet format. Processed data were used to calculate soil water storage within and below the citrus root zone at desired time intervals. Irrigation set points (i.e., full point equivalent to maximum desirable water storage and refill points I and II) were defined based on field capacity determined both in the field and in the laboratory and permanent wilting point. It was possible to maintain the water content in the root zone between the full and refill points I and II during most of the growing season. Although soil water content in the root zone exceeded the full point during periods of high irrigation, it drained rapidly within 24–48 h after the end of such irrigation events. Using soil moisture depletion in the root zone during periods of low water application to estimate citrus evapotranspiration (ET), the calculated daily average ET during 10-day period in November was 1.33 mm day⁻¹. Received: 11 August 1998     

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%。     

Retrieving Soil Moisture Storage in the Unsaturated Zone Using Satellite Imagery and Bi-Annual Phreatic Surface Fluctuations

Ongoing research into net groundwateruse in Pakistan needed soil moisturestorage information to compute monthlysoil water balances. A methodology isdeveloped to retrieve soil moisture storagein the complete unsaturated zone from rootzone soil moisture content (based onthermal satellite imagery) and bi-annualphreatic surface fluctuations. A root meansquare error in volumetric soil moisturecontent of 0.05 cm³ cm^-3 in theroot zone of irrigated fields was found forthe case study in Pakistan. A new simpleparameterisation of matric pressure headdistribution between the root zone and thephreatic surface was developed. Theabsolute root mean square error in dailyestimates of unsaturated zone storage forshallow (2 m) and deep groundwater tables(10 m) was found to be 7 cm (the averagetotal storage is 110 cm). It is concludedthat the spatial variation of the soilmoisture storage depends on the depth ofthe phreatic surface, whereas the temporalvariation is mainly controlled by the rootzone soil moisture changes. The resultsshow that for an area of 3 million ha, storagechanges of ± 10 cm month^-1 occur,which is a significant quantity for monthlywater balance analysis. Conventionalmethods such as specific yield do notconsider moisture changes in the irrigatedtop soil when the groundwater table isdeep. The new method is, therefore, apossible alternative solution, especiallyin areas where hydrological data isscanty.     

Cotton root growth as affected by changes in soil water distribution and their impact on plant tolerance to drought

The capability of mature cotton plants (Gossypium hirsutum L.) to adjust to progressive drying of their root zone by promoting root growth to adjacent wetted zones, and the implications of this process on irrigation design were investigated. Field grown plants that developed shallow root systems in response to a drip irrigation management of daily, surface soil wettings were exposed 85 days after emergence (DAE), while in the flowering stage, to a sudden change in water distribution in the form of deep soil wetting (DSW) followed by termination of irrigation. The shallow rooted plants (SRP) failed to respond to further surface soil wetting and the progressive drying of the profile by rapid root growth to the deeper-wetted zones; consequently, the SRP suffered from water deficiency for at least two weeks, evidenced by a gradual decrease in their leaf water potential (L_w). Potted plants responded similarly. Daily irrigations of the pot surface with water amounts similar to those lost by evapotranspiration led to the development of a system in which most of the roots and available water became concentrated at the pot's upper section. A transition to irrigation from the bottom of the pot led to a reversed soil-water content gradient and failed to promote rapid root spreading to the deeper-wetted layers, in spite of the accelerated drying of the upper zone. The slow deepening of the root system was accompanied by water-stress symptoms as indicated by a considerable reduction in dry matter production. The root shoot ratio in these plants was not much greater than in non-stressed plants in which the surface wetting was continued. This indicated that preferential root growth relative to the shoot did not occur in response to the progressive drying of the shallow root zone. Rewetting of the root zone after a long period of soil water deficiency failed to promote rapid recovery of the root system in the form of root regrowth in this zone. It was concluded that the capability of mature cotton plant roots to adjust their growth to large changes in water distribution in the soil, is slow and that this should be taken into account when determining an irrigation regime in which the depth at which water is applied is changed during the growing season.Contribution from the Agricultural Research Organization, Volcani Center, Bet Dagan, Israel; No. 343-E, 1992 series     

Soil-dependent wetting from trickle emitters: implications for system design and management

For trickle irrigation systems to deliver improved water- and nutrient-use efficiency, distance between emitters and emitter flow rates must be matched to the soil's wetting characteristics and the amount and timing of water to be supplied to the crop. Broad soil texture ranges (e.g. sand, loam, clay) are usually the only information related to soil wetting used in trickle system designs. In this study, dimensions of wetted soil were calculated from hydraulic properties of 29 soils covering a wide range of textures and soil hydraulic properties to assess the impact of soil texture and/or type on soil wetting patterns. The soils came from two groups that differed in the extent to which hydraulic properties depended on soil texture. Vertical and radial distances to the wetting front from both surface and buried emitters were calculated for conditions commonly associated with daily irrigation applications in a widely spaced row crop (sugarcane) and horticultural crops. In the first group of soils, which had least expression of field structure, the wetted volume became more spherical (i.e. the wetted radius increased relative to the depth of wetting below the emitter) with increasing clay content, as is commonly accepted. However, in the second group of soils in which field structure was preserved, there was no such relationship between wetted dimensions and texture. For example, five soils with the same texture had as great a variation in wetting pattern, as did all 11 soils in the first group, indicating the considerable impact of field structure on wetting patterns. The implications of the results for system design and management were illustrated by comparing current recommendations for trickle irrigation systems in coastal northeastern Australia with the calculated wetted dimensions. The results suggest that (1) emitter spacings recommended for sugarcane are generally too large to allow complete wetting between emitters, and (2) the depth of wetting may be greater than the active root zone for both sugarcane and small crops in many soils, resulting in losses of water and chemicals below the root zone. We conclude that texture is an unreliable predictor of wetting and there is no basis for adopting different dripper spacing in soils of different textures in the absence of site-specific information on soil wetting. Such information is crucial for the design of efficient trickle irrigation systems.Communicated by J. Annandale     

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。     

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.     

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。     

Seasonal water use by winter wheat grown under shallow water table conditions

Techniques for estimating seasonal water use from soil profile water depletion frequently do not account for flux below the root zone. A method using tensiometers for obtaining evapotranspiration losses from the root zone and water movement below it is discussed. Soil water flux below the root zone is approached by a sequence of pseudo steady state solutions of the flow equation. Upward soil water flux contributed 36 to 73% to the total water requirement of winter wheat (Triticum aestivum L.) whereas soil water depletion accounted for 11 to 19% only. Water use efficiency with one irrigation during an early stage of plant development is greater than with no or three irrigations. This is the result of both decrease of resistance due to soil moistening and better root development. Tensiometer readings were also interpreted to estimate root zones, water table depths and soil moisture contents. Methods described in this paper can be used in determining seasonal water use by growing crops, replacing or supplementing lysimeter or meteorology approaches to this problem.