Water use by alfalfa,maize, and barley as influenced by available soil water

The availability of soil water is one of the most important determinants of crop production. Field studies were conducted to examine the relationships between relative evapotranspiration ($\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$) and available water (W) for alfalfa, maize, and barley. Line source sprinkler irrigation systems were used to provide the variations in soil moisture. Actual evapotranspiration (E) was determined using the water balance method. Maximum evapotranspiration (E_max) was the highest E observed among all irrigation levels. Potential evapotranspiration (E₀) was estimated using Penman's equation to characterize the evaporative demand.The results show that the relationships between $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ and W were different for the three crops. For alfalfa, the relationship was dependent on the physical properties of the soil and on E₀. In a clay loam soil, the decline in E from E_max commenced at a higher value of W than in a sandy loam soil. Furthermore, the rate of decline in E from E_max was dependent on E₀ and was greater as E₀ increased. In the sandy loam soil, the relationship between $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ and W was not dependent on E₀. For maize and barley in clay loam soils, $\text{E}\text{E}{}_{\mathrm{<mtext>max</mtext>}}$ as a function of W was linear, and was not dependent on E₀. This study was compared to results reported in the literature, and it was hypothesized that differences were related mainly to the way variation in soil moisture was introduced over the measurement period.     

Hydraulic conductivity and clay dispersion as affected by application sequence of saline and simulated rain water

Summary Saturated hydraulic conductivity HC, and degree of clay dispersion DD, were determined for a sandy loam and a clay loam soil with waters of different combinations of sodium adsorption ratios SAR (5, 15, 30 and 45 mmol^1/2l^–1/2) and total electrolyte concentration TEC (15, 30, 60 and 90 me l^–1) followed by distilled water to simulate rainwater. Increase in SAR and decrease in TEC of leaching water increased DD and decreased HC of soils. The HC values were more highly correlated with SAR than TEC. The critical ratio of TEC/SAR of water below which the relative HC is less than the hreshold value (i.e. 0.75) was 3.82 and 2.01 for clay loam and sandy loam, respectively taking the HC of initial soil with good quality water (SAR = 0.5, EC = 0.3dS m^–1) as the reference. Drastic reductions in conductivity were observed even at SAR = 5 (60–83%) when saline water was displaced by rainwater, sensitivity being greater for the sandy loam than for the clay loam; recovery was negligible when the saline water was again applied. Data of EC and clay content of the effluent on application of distilled water suggested that clay dispersion, its movement and lodgement into conducting pores, may be the major cause of HC reduction in sandy loam, whereas in clay loam, surface sealing is the major cause. With distilled water application HC values were governed by SAR rather than TEC of initial water used. The study thus suggests that existing water quality criterion may underestimate the real soil permeability hazards from saline-sodic waters during rainfall infiltration in monsoon season.     

The effect of organic manuring and water quality on water transmission parameters and sodication of a sandy loam soil

Water transmission characteristics under saturated and unsaturated conditions were studied in a sandy loam soil with (F₁) and without (F₀) long-term farmyard manure (FYM) treatments, in relation to sodium adsorption ratios (SAR) and electrolyte concentrations of water. The effect of FYM and ratios of Ca²⁺ : Mg²⁺ in water at a given SAR on sodication of the soil was also studied.Saturated hydraulic conductivity (k) and weighted mean diffusivity ($\text{D}\text{?}$) were slightly higher for F₁ than for F₀, whereas sodication indices like Gapon constant (K_G), Krishnamoorthy-Davis-Overstreet constant (K_KDO) and Vanselow constant (K_V) were slightly smaller. The k and $\text{D}\text{?}$ decreased with an increase of SAR and decrease of electrolyte concentration, the effect of SAR being more pronounced. There was proportionately a sharper decrease in the k and $\text{D}\text{?}$ values at SAR 10 with total electrolyte concentrations of 10–40 meq 1^?1. However, with a total electrolyte concentration of 80 meq 1^?1, there was a smaller drop at SAR 10.A small difference in the build-up of exchangeable sodium percentage (ESP) in F₁ and F₀ treatments at a given SAR suggests that, apart from slightly improving water transmission parameters, the use of FYM also reduces the sodication hazard in a soil irrigated with sodic waters. An increase in the Ca²⁺ : Mg²⁺ ratio from 25:75 to 75:25 slightly decreased the values of K_G, K_KDO and K_V, thus indicating somewhat more preference for Ca²⁺ to Mg²⁺ at a given SAR, which was more so in F₁ soil. This fact could also be expressed in terms of a slight shift of thermodynamic exchange constant (K) and standard free energy change of the exchange reaction (ΔG⁰_r). The presence of some unidentified Na⁺ releasing minerals in the soils studied was observed and correction for exchangeable Na⁺ determination applied.     

An analysis of the effect of the vertical fissuring in mole-drained soils on drain performances

Numerical solutions of the seepage equation of groundwater flow were used in an analysis of the effect on drain performance of the herring-bone pattern of vertical fissuring, with fractures fanning out from the central slit, in mole-drained soils. Drain performances were assessed from values of the dimensionless parameter $\text{W}{}_{\mathrm{<mtext>m</mtext>}}\text{=}\text{2E}{}_{\mathrm{<mtext>m</mtext>}}\text{qD}{}^2$, where E_m is the ‘seepage potential’ at the position of maximum water-table height when the steady rainfall is q and the drain spacing is 2D. W_m decreased with increase in the length of the fractures and, to a lesser extent, with decrease in the spacing of them, showing that the fracturing enables a mole-drainage system to cope with higher rainfall rates and to produce more rapid water-table drawdowns.     

Wheat root distribution,water extraction pattern and grain yield as influenced by time and rate of irrigation

The effect of first irrigation (26, 40 and 54 days after seeding) and the rate of irrigation (5.5, 7.5 and 9.5 cm) applied subsequently at $\text{IW}\text{E}{}_{\mathrm{<mtext>pan</mtext>}}$ ratio of 0.9 on wheat root distribution, water extraction pattern and grain yield was studied on a barrier-free, sandy loam soil. The crop developed a more extensive root system when the first irrigation was applied after 26 days than after 40 and 54 days. With the first irrigation on the 26th day, the crop, receiving subsequent irrigations less frequently but at a heavier rate, developed a deeper root system than the crop receiving frequent, light irrigations. The water extraction pattern corresponded with the root distribution pattern. A relatively small difference in root density in the deeper layers caused a greater difference in soil water content than in the upper layers. Light and frequent irrigations produced maximum grain yields. However, for developing an extensive root system and enhancing water utilization in the subsoil, an early, light irrigation with subsequent irrigations applied less frequently at a relatively heavier rate seems desirable.     

Evaluation of a crop water stress index for irrigation scheduling of bermudagrass

This study was conducted to assess crop water stress index (CWSI) of bermudagrass used widely on the recreational sites of the Mediterranean Region and to study the possibilities of utilization of infrared thermometry to schedule irrigation of bermudagrass. Four different irrigation treatments were examined: 100% (I₁), 75% (I₂), 50% (I₃), and 25% (I₄) of the evaporation measured in a Class A pan. In addition, a non-irrigated treatment was set up to determine CWSI values. The status of soil water content and pressure was monitored using a neutron probe and tensiometers. Meanwhile the canopy temperature of bermudagrass was measured with the infrared thermometry. The empirical method was used to compute the CWSI values. In this study, the visual quality of bermudagrass was monitored seasonally using a color scale. The best visual quality was obtained from I₁ and I₂ treatments. Average seasonal CWSI values were determined as 0.086, 0.102, 0.165, and 0.394 for I₁, I₂, I₃, and I₄ irrigation treatments, respectively, and 0.899 for non-irrigated plot. An empirical non-linear equation, Qave=1+⌊6[1+(4.853 CWSIave)^2.27]^−0.559⌋$Q_{\text{ave}}=1+⌊6{[1+{(4.853\text{CWS}{\text{I}}_{\text{ave}})}^{2.27}]}^{-0.559}⌋$, was deduced by fitting to measured data to find a relation between quality and average seasonal CWSI values. It was concluded that the CWSI could be used as a criterion for irrigation timing of bermudagrass. An acceptable color quality could be sustained seasonally if the CWSI value can be kept about 0.10.     

Compressibility of Some Trinidadian Soils as Affected by the Incorporation of Peat

The effect on compressibility of incorporating peat into four remoulded Trinidadian agricultural soils was investigated over a range of stresses from 0 to 1000 kPa using a compression machine. Air-dry peat was applied at four levels (0, 4, 8 and 12% by mass) to the soils (two sandy loams, clay loam and clay) and tested at three moisture contents close to the Proctor optimum moisture content of the soils. Compression curves (bulk density versus log applied stress) for each soil at the moisture levels tested were almost linear and parallel over the range of stresses from about 100 to 1000 kPa.Mean values of dry bulk density declined significantly at 0.001 level with increasing peat content from 1·23 to 0·87 Mg m^-3. Mean bulk density values increased significantly at 0·001 level with increasing applied stress and moisture content and declined with increasing clay content. Significant interaction effects were observed between soil type and peat content and between peat content and moisture content. Peat incorporation resulted in greater soil compression, but the increases were less evident in clay than in sandy loam soils. Soil compression refers to the decrease in soil volume with the application of external load. The compression index, C (slope of the dry bulk density versus log applied stress relationship), increased significantly at 0·05 level from 0·21 Mg/m³ in one sandy loam soil to 0·38 Mg/m³ in the clay soil. While the C value did not differ significantly with increasing peat content in the sandy loams and the clay loam, it decreased significantly at 0·01 level in the clay soil. An equation expressing C as a function of initial soil bulk density before compression and a strain parameter was developed in order to explain the variation of C in the soils tested. A method is described that can be adopted to quantify the effect of peat on soil compressibility.     

Performance evaluation and calibration of soil water content and potential sensors for agricultural soils in eastern Colorado

This study evaluated the performance of three soil water content sensors (CS616/625, Campbell Scientific, Inc., Logan, UT; TDT, Acclima, Inc., Meridian, ID; 5TE, Decagon Devices, Inc., Pullman, WA) and a soil water potential sensor (Watermark 200SS, Irrometer Company, Inc., Riverside, CA) in laboratory and field conditions. Soil water content/potential values measured by the sensors were compared with corresponding volumetric water content (θ_v, m³ m⁻³) values derived from gravimetric samples, ranging approximately from the permanent wilting point (PWP) to field capacity (FC) volumetric water contents. Under laboratory and field conditions, the factory-based calibrations of θ_v did not consistently achieve the required accuracy for any sensor in the sandy clay loam, loamy sand, and clay loam soils of eastern Colorado. Salt (calcium chloride dihydrate) added to the soils in the laboratory caused the CS616, TDT, and 5TE sensors to experience errors in their volumetric water content readings with increased bulk soil electrical conductivity (EC; dS m⁻¹). Results from field tests in sandy clay loam and loamy sand soils indicated that a linear calibration (equations provided) for the TDT, CS616 and 5TE sensors (and a logarithmic calibration for the Watermark sensors) could reduce the errors of the factory calibration of θ_v to less than 0.02 ± 0.035 m³ m⁻³. Furthermore, the performance evaluation tests confirmed that each individual sensor needed a unique calibration equation for every soil type and location in the field. In addition, the calibrated van Genuchten (1980) equation was as accurate as the calibrated logarithmic equation and can be used to convert soil water potential (kPa) to volumetric soil water content (m³ m⁻³). Finally, analysis of the θ_v field data indicated that the CS616, 5TE and Watermark sensor readings were influenced by diurnal fluctuations in soil temperature, while the TDT was not influenced. Therefore, it is recommended that the soil temperature be considered in the calibration process of the CS616, 5TE, and Watermark sensors. Further research will be aimed towards determining the need of sensor calibration for every agricultural season.     

滴灌条件下山区典型土壤水分运移规律分析

在广西山区选择沙土、壤土和黏土等3种典型土壤,并开展滴灌在这3种土壤条件下的土壤水分运移规律研究。试验结果表明:1在地埋黏土、壤土和沙土以及0.10 MPa工作压力条件下,滴灌管的单米流量为4.17、5.92和6.10 L/h,为地表自由出流的67.58%、95.05%和98.87%;2滴灌在黏土的水分运移形状基本为圆形,在沙土和壤土的湿润形状为上小下大的椭圆形;3同等条件下,水分在沙土的水平和垂直向下运移速率最大,壤土次之,黏土最小;4在土箱相同位置,黏土的土壤含水率最大,壤土次之,沙土最小;5根据滴灌的土壤水分运移规律,提出滴灌管在广西山区沙土、壤土和黏土的适宜埋深分别为10、15和20 cm;6滴灌应用在山区条播作物时,在黏土、壤土、沙土的适宜滴孔间距应为35、30和25 cm。     

Estimating in situ soil–water retention and field water capacity in two contrasting soil textures

A priori knowledge of the in situ soil field water capacity (FWC) and the soil-water retention curve for soils is important for the effective irrigation management and scheduling of many crops. The primary objective of this study was to estimate the in situ FWC using the soil-water retention curve developed from volumetric water content (θ), and water potential (ψ) data collected in the field by means of soil moisture sensors in two contrasting-textured soils. The two study soils were Lihen sandy loam and Savage clay loam. Six metal frames 117 cm × 117 cm × 30 cm high were inserted into the soil to a depth of 5–10 cm at approximately 40 m intervals on a 200 m transect. Two Time Domain Reflectrometry (TDR) sensors were installed in the center of the frame and two Watermark (WM) sensors were installed in the SW corner at 15 and 30 cm depths to continuously monitor soil θ and ψ, respectively. A neutron probe (NP) access tube was installed in the NE corner of each frame to measure soil θ used for TDR calibration. The upper 50–60 cm of soil inside each frame was saturated with intermittent application of approximately 18–20 cm of water. Frames were then covered with plastic tarps. The Campbell and Gardner equations best fit the soil–water retention curves for sandy loam and clay loam soils, respectively. Based on the relationship between soil ψ and elapsed time following cessation of infiltration, we calculated that the field capacity time (t _FWC) were reached at approximately 50 and 450 h, respectively, for sandy loam and clay loam soils. Soil-water retention curves showed that θ values at FWC (θ _FWC) were approximately 0.228 and 0.344 m³ m⁻³, respectively, for sandy loam and clay loam soils. The estimated θ _FWC values were within the range of the measured θ _FWC values from the NP and gravimetric methods. The TDR and WM sensors provided accurate in situ soil–water retention data from simultaneous soil θ and ψ measurements that can be used in soil-water processes, irrigation scheduling, modeling and chemical transport.     

Irrigation, tillage and mulching effects on soybean yield and water productivity in relation to soil texture

Depleting groundwater resources in Indian Punjab call for diversifying from rice to crops with low evapo-transpiration needs and adopting water-saving technologies. Soybean offers a diversification option in coarse- to medium-textured soils. However, its productivity in these soils is constrained by high soil mechanical resistance and high soil temperature during early part of the growing season. These constraints can be alleviated through irrigation, deep tillage and straw mulching. This 3-years field study examines the individual and combined effects of irrigation, deep tillage, and straw mulching regimes on soybean yield and water productivity (WP) in relation to soil texture. Combinations of two irrigation regimes viz., full irrigation (I_f), and partial irrigation (I_p) in the main plot; two tillage regimes viz., conventional-till (CT)-soil stirring to 0.10 m depth, and deep tillage (DT)-chiseling down to 0.35 m depth followed by CT in the subplot; and two mulch rates viz., 0 (M₀) and 6 t ha⁻¹ (M) in the sub-subplot on two soils differing in available water capacity were evaluated.Seed yield was greater in the sandy loam than in the loamy sand reflecting the effects of available water capacity. Irrigation effects were greater on loamy sand (40%) than on sandy loam (5%) soil. Deep tillage benefits were also more on loamy sand (14%) compared to sandy loam (5%) soil. Yield gains with mulching were comparable on the two soils (19%). An evaluation of interaction effects showed that mulching response was slightly more in I_p (20%) than in I_f regimes (17%) in the sandy loam; while in the loamy sand, mulching gains were comparable (18-19%) in both irrigation regimes. Benefits of deep tillage in the loamy sand soil were more in I_p (20%) than in I_f regimes (17%). Deep tillage and straw mulching enhanced WP (ratio of seed yield/water use) from 1.39 to 1.97 kg ha⁻¹ mm⁻¹ in I_p regime, and from 1.87 to 2.33 kg ha⁻¹ mm⁻¹ in I_f regime in the loamy sand soil. These effects on WP were less in the sandy loam soil with greater available water capacity. Yield and WP gains are ascribed to deeper and denser rooting due to moderation of soil temperature and water conservation with straw mulching and tillage-induced reduction in soil mechanical resistance. Root mass in CTM₀, CTM, DTM₀ and DTM was 2.79, 5.88, 5.34 and 5.58 mg cm⁻² at pod-filling in the loamy sand soil. Comparable yield responses to deep tillage or mulching in the loamy sand soil suggest that either of the options, depending on their cost and availability considerations, can be employed for improving soybean yield and water productivity.     

毛细节水灌溉条件下蔗区土壤水分运移规律研究

毛细节水灌溉作为一种类似滴灌的新型灌溉技术逐渐得到关注。在室内模拟了毛细管水分在蔗区沙土、壤土和黏土中的运移情况。通过室内试验和HYDRUS-3D建模分析表明:土壤类型对土壤各方向入渗有明显的影响,水分运移速度和土壤各方向湿润范围顺序为:沙土壤土黏土;3种土壤含水率等值线变化规律基本一致,同样湿润位置土壤含水率顺序为:黏土壤土沙土。根据毛细管的水分在沙土、壤土和黏土运移规律,提出毛细管在蔗区沙土、壤土和黏土的合理埋深应为40、30和20cm。     

分形在土壤空间变异性评价中的应用研究

针对土壤空间变异性问题,研究了分维数和土壤空间变异性的关系。应用Green-Ampt入渗模型模拟出十种土壤的下渗湿峰深度值,它们的大小依次是:壤质砂土、沙壤土、沙质黏壤土、壤土、粉砂壤土、砂质壤土、黏质壤土、粉砂黏壤土、黏土、粉砂黏土,然后计算出十种土壤随机组合构成的100种土壤剖面的湿峰形状分维数,用这些分维数来描述土壤空间变异性。同时用反距离加权法和相邻两参数平方均值法算出土壤区域属性值,并与分维数进行比较,再通过对土壤空间变异性(用土壤饱和水力传导度来表示)的统计分析和分维数关系的分析,得出湿峰的分形维数与KS具有较明显的分带关系,而且这种关系在实际流域中会更明显。总的来说,土壤空间变异性越大,分形维数df越大。因此可以看出,用分形来评价土壤空间变异性是可行的,并取得了不错的效果。     

Effect of water quality on soil structure and infiltration under furrow irrigation

The quality of irrigation water has the potential to significantly affect soil structural properties, infiltration and irrigation application efficiency. While the effect of electrolyte concentration (as indicated by the electrical conductivity EC) and sodium adsorption ratio (SAR) have been studied under laboratory conditions, the effect on soil profile structural properties and irrigation performance have not been widely investigated under field conditions. In this paper, water with three different levels of sodium (SAR = 0.9, 10 and 30) was applied as alternative treatments to a clay loam soil. The application of 238–261 mm of medium- to high-SAR water was found to reduce aggregate stability, increase the bulk density of both the surface crust and underlying soil, and reduce the total depth of infiltration and final infiltration rate. Where low-SAR water was used, there was no significant (P<0.05) difference in final infiltration rate after the first four irrigations. However, where moderate- and high-SAR water was applied after the first four irrigations with the low EC-SAR water, the final infiltration rate was found to decrease on each of the successive irrigation events. For the moderate- and high-SAR treatments, this suggests that a steady-state equilibrium had not been reached within that part of the soil profile impeding infiltration. It is proposed that the initial reduction in infiltration is related to the physical processes of slaking leading to the development of an apedal, hardsetting surface soil layer. Similarly, it is proposed that the subsequent increase in bulk density and decline in infiltration where moderate and high EC-SAR water is applied is due to an increase in clay tactoid swelling reducing the size of the conducting micropores, dispersion blocking pores, and/or an increase in the thickness of the apedal surface layer. The reduction in infiltration associated with the use of high-SAR irrigation water was found to reduce the performance of the irrigations, with the application efficiency of the final irrigation decreasing from 40% where the low-SAR water was used, to 21% where the high-SAR water was applied. The implications for surface irrigating with water containing high sodium levels are discussed.Communicated by A. Kassam     

Changes in hydraulic conductivity of soils varying in calcite content under cycles of irrigation with saline-sodic and simulated rain water

Soil infiltration problems occur as a result of alternating irrigation with saline-sodic waters and monsoon rainfall. Hydraulic conductivity (K) and related soil properties of a non-calcareous (CaCO₃ 0.8%) and a calcareous soil (25.7%) having similar textural constituents were monitored. The soils were subjected to six consecutive cycles of irrigation with saline waters (SW) of sodium adsorption ratio (SAR), 10, 20 or 30 (mmol/l)^1/2, but of similar electrolyte concentration (EC; 80 mEq/l), and each followed by simulated rain water (SRW) (electrical conductivity <0.02 dS/m). Results are presented in terms of relative K i.e. K _r=K _sw/K _tw where K _tw is steady state K measured separately under application with tap water (ECw 0.54 dS/m, SAR 0.9). For irrigation with SW alone, K _r values were reduced to 0.95, 0.79 and 0.70 at SAR of 10, 20 and 30, respectively, in non-calcareous soil. The corresponding values of 0.95, 0.87 and 0.79 were slightly higher in calcareous soil. Severe reductions in K _r were observed in both the soils when subjected to alternate use of SW and SRW (K _r=0.22, 0.03 and 0.02 in non-calcareous, and 0.57, 0.17 and 0.07 in calcareous soil). About half of the reductions in K _r were reversible when SW was subsequently applied. Depth distributions of salinity, pH, dispersible clay and hydraulic head indicate that disaggregation and dispersion of surface soil was the cause of reduced K with SRW, whereas “washed in” sub-soil became restrictive and controlled the K values with SW under alternations of SW and SRW. Salt release (<1 mEq/l) was insufficient to avoid dispersion and sustain K even in the calcareous soil. For evaluating the infiltration hazard of saline-sodic water, measurements of stabilized K values after consecutive cycles of SW and SRW should serve as a better diagnostic criteria under monsoonal climates than threshold EC–SAR combinations. Received: 8 June 1998     

Effects of irrigation using treated wastewater on table grape vineyards: dynamics of sodium accumulation in soil and plant

The effect of using treated wastewater for irrigation of table grapes (Vitis vinifera cv. Superior Seedless) was studied for six seasons. The experimental vineyard was grown on clay loam soil in a semi-arid area. Treated wastewater (5.83 meq L^?1 Na⁺) with (TWW + F) and without (TWW) fertilizer, and fresh water with fertilizer (FW + F, 2.97 meq L^?1 Na⁺), were each applied at three irrigation levels (80, 60 and 40 % of crop evapotranspiration before harvest). Root zone (0–60 cm soil depth) soil saturated paste extract Na⁺ concentrations and sodium adsorption ratio (SAR) values fluctuated over the years, but generally decreased in the order TWW > TWW + F > FW + F for each irrigation level. Both Na⁺ concentrations and SAR values developed faster and to a greater extent at higher irrigation. Adding fertilizer to TWW decreased Na⁺ and SAR only at the high irrigation level. Na⁺ concentrations in the trunk wood, bark and xylem sap of the TWW and TWW + F irrigated vines were significantly higher than those in the FW + F-irrigated vines. Leaf petiole Na⁺ content increased with time and its maximum value in TWW and TWW + F irrigated vines exceeded 6,500 mg kg^?1, threefold higher than in FW + F irrigated vines. We conclude that in clay soils under relatively high irrigation, Na⁺ may pose a greater potential risk to plants and soil rather than Cl^? or salinity per se. However, significant effects on yield were not recorded during this six-year study probably due to the high salinity tolerance of the ‘Paulsen’ rootstock used in the experiment.     

滴灌和微润灌条件下桂西北山区典型土壤水分运移规律分析

为了研究滴灌和微润灌在广西山区主要土壤的水分运移规律,在广西山区选择砂土、壤土和黏土等三种典型土壤,在室内建立并开展土壤水分运移规律试验。试验结果表明:1在地埋黏土、壤土和砂土以及0.10 MPa工作压力条件下,微润管的单米流量分别为0.24、0.31和0.43L/h,为地表出流量的67.6%~98.8%,滴灌管的单米流量为4.17、5.92和6.10L/h,为地表出流量的38.1%~68.2%;2在3种土壤中,滴灌和微润灌的水分运移形状初期为圆形,后期为椭圆形,但砂土的湿润范围最大、壤土次之、黏土最小;3在土箱相同位置,黏土的土壤含水率最大,壤土次之,砂土最小;4根据滴灌和微润灌的土壤水分运移规律,提出滴灌管和微润管在砂土、壤土的适宜埋深为20cm,在黏土的适宜埋深为10cm。