Simulation of point source wetting pattern of subsurface drip irrigation

Laboratory experiments and calculations were carried out to analyze the effect of subsurface drip irrigation (SDI) design features on soil wetting patterns for a point source. Experimental and simulated soil wetting patterns, using the SWMS-2D (simulating water movement and solute transport in two-dimensional) Galerkin finite element model, were investigated to maximize the efficiency of water saving. The analysis addressed the influence of water pressure head, back pressure and emitter diameter on wetting patterns. Predictions of water content distributions in the soils made with SWMS-2D were found to be in good agreement with the observed data. Results showed that this model provides confidence that model predictions are not too sensitive to back-pressure effects.     

Analysis of soil wetting and solute transport in subsurface trickle irrigation

The increased use of trickle or drip irrigation is seen as one way of helping to improve the sustainability of irrigation systems around the world. However, soil water and solute transport properties and soil profile characteristics are often not adequately incorporated in the design and management of trickle systems. In this paper, we describe results of a simulation study designed to highlight the impacts of soil properties on water and solute transport from buried trickle emitters. The analysis addresses the influence of soil hydraulic properties, soil layering, trickle discharge rate, irrigation frequency, and timing of nutrient application on wetting patterns and solute distribution. We show that (1) trickle irrigation can improve plant water availability in medium and low permeability fine-textured soils, providing that design and management are adapted to account for their soil hydraulic properties, (2) in highly permeable coarse-textured soils, water and nutrients move quickly downwards from the emitter, making it difficult to wet the near surface zone if emitters are buried too deep, and (3) changing the fertigation strategy for highly permeable coarse-textured soils to apply nutrients at the beginning of an irrigation cycle can maintain larger amounts of nutrient near to and above the emitter, thereby making them less susceptible to leaching losses. The results demonstrate the need to account for differences in soil hydraulic properties and solute transport when designing irrigation and fertigation management strategies. Failure to do this will result in inefficient systems and lost opportunities for reducing the negative environmental impacts of irrigation.Communicated by J. Annandale     

利用工程措施改变地下滴灌土壤湿润模式的试验

通过滴灌带下铺设阻水塑料布,明显地改变了地下滴灌湿润体的形状和湿润体内部的土壤水分分布,与普通地下滴灌比较,增大了沿毛管纵向的湿润宽度,提高了湿润锋向上的运移高度,减小了水分向下的入渗深度,同时,增大了滴灌带上层土壤的含水量。     

Response of green bean (P. vulgaris L.) to subsurface drip irrigation and partial rootzone-drying irrigation

Effects on water use, green bean yield, irrigation water-use efficiency (IWUE), water-use efficiency (WUE), plant dry weight and crop water relationship were investigated for two-drip irrigation techniques and four irrigation water levels in the Mediterranean region of Turkey. The treatments were conventional (SDI) and alternating subsurface drip irrigation (SPRD). At each irrigation event, half of the volume of water applied to the SDI was applied to one side of the crop, representing the partial rootzone-drying treatment. All treatments received 295 mm of irrigation during crop establishment, prior to beginning the different irrigation regimes. Differing irrigation amounts corresponded to four crop-pan coefficients (Kcp₁ = 0.6, Kcp₂ = 0.8, Kcp₃ = 1.0 and Kcp₄ = 1.2), appropriate to pan data. Total water applied to the SDI and SPRD treatments ranged from 366 to 437 mm and from 331 to 366 mm, respectively, depending on Kcp values, with water uptake varying from 396 to 470 mm and 364 to 409 mm, respectively. While differences of green bean yield and dry plant weights were not significantly affected by the SDI and SPRD irrigation techniques, the overall irrigation water saving was found to be 16% for the SPRD irrigation treatment compared with the SDI treatment. SPRD irrigation techniques increased IWUE, WUE, and slopes of yield water relationships. Increase in slopes of the yield–irrigation water and yield–water-use function of SPRD according to the equivalent slopes of the SDI were 215.8 and 151.4%, respectively. SPRD increased the green bean yield response factor (ky) with value of 128.4% according to the equivalent slopes of the SDI. In conclusion, irrigation scheduling based on a 0.8 crop-pan coefficient is recommended for conventional SDI, with 1.0 being more appropriate for partial rootzone-drying practice.     

Comparison of numerical, analytical, and empirical models to estimate wetting patterns for surface and subsurface drip irrigation

Due to increasing competition for water resources by urban, industrial, and agricultural users, the proportion of agricultural water use is gradually decreasing. To maintain or increase agricultural production, new irrigation systems, such as surface or subsurface drip irrigation systems, will need to provide higher water use efficiency than those traditionally used. Several models have been developed to predict the dimensions of wetting patterns, which are important to design optimal drip irrigation system, using variables such as the emitter discharge, the volume of applied water, and the soil hydraulic properties. In this work, we evaluated the accuracy of several approaches used to estimate wetting zone dimensions by comparing their predictions with field and laboratory data, including the numerical HYDRUS-2D model, the analytical WetUp software, and selected empirical models. The soil hydraulic parameters for the HYDRUS-2D simulations were estimated using either Rosetta for the laboratory experiments and inverse analysis for the field experiments. The mean absolute error (MAE) was used to compare the model predictions and observations of wetting zone dimensions. MAE for different experiments and directions varied from 0.87 to 10.43 cm for HYDRUS-2D, from 1 to 58.1 cm for WetUp, and from 1.34 to 12.24 cm for other empirical models.     

Simulation of soil water dynamics under subsurface drip irrigation from line sources

A mathematical model which describes water flow under subsurface drip lines taking into account root water uptake, evaporation of soil water from the soil surface and hysteresis in the soil water characteristic curve θ(H) is presented. The model performance in simulating soil water dynamics was evaluated by comparing the predicted soil water content values with both those of Hydrus 2D model and those of an analytical solution for a buried single strip source. Soil water distribution patterns for three soils (loamy sand, silt, silty clay loam) and two discharge rates (2 and 4 l m⁻¹ h⁻¹) at four different times are presented. The numerical results showed that the soil wetting pattern mainly depends on soil hydraulic properties; that at a time equal to irrigation duration decreasing the discharge rate of the line sources but maintaining the applied irrigation depth, the vertical and horizontal components of the wetting front were increased; that at a time equal to the total simulation time the discharge rate has no effect on the actual transpiration and actual soil evaporation and a small effect on deep percolation. Also the numerical results showed that when the soil evaporation is neglected the soil water is more easily taken up by the plant roots.     

Effect of high frequency surface and subsurface drip irrigation on root distribution of sweet corn

Summary Characterization of root growth and distribution is fundamental in explaining crop responses to irrigation and in determining appropriate management of irrigation systems, particularly with drip systems since it is widely believed that drip irrigation may limit the extent of root development. An experiment was conducted to study root distribution of sweet corn grown under high frequency surface (S) and subsurface (SS) drip irrigation, fertilized daily through drip systems at three phosphorus levels of P₀ (no injected P), P₁ (P injected at 67 kg/ha) and P₂ (P injected at 134 kg/ha). Root sampling at the end of the growing season indicated that: (1) Root extension continued at depths in excess of 2 m in both the surface and subsurface drip at all P levels. (2) The greatest differences between SS and S treatments were observed in the top 45 cm depth. Higher root length density was observed in the surface 30 cm in S plots while the sweet corn in the SS plots had greater root length density than S plots below 30 cm, and (3) the greater root length density in the SS irrigated sweet corn was not reflected in a similar increase in total above-ground dry matter.This project was partially supported by a grant from BARD Project no I-1116-86     

Effect of subsurface drip irrigation on onion yield

Subsurface drip system is the latest method of irrigation. The design of subsurface drip system involves consideration of structure and texture of soil, and crop’s root development pattern. A 3-year experiment was conducted on onion (Allium Cepa L., cv. Creole Red) in a sandy loam soil from October to May in 2002–2003, 2003–2004 and 2004–2005 to study the effect of depth of placement of drip lateral and different levels of irrigation on yield. Tests for uniformity of water application through the system were carried out in December of each year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and six placement depths of the drip laterals (surface (0), 5, 10, 15, 20 and 30 cm) were maintained in the study. Onion yield was significantly affected by the placement depth of the drip lateral. Maximum yield (25.7 t ha⁻¹) was obtained by applying the 60.7 cm of irrigation water and by placing the drip lateral at 10 cm soil depth. Maximum irrigation water use efficiency (IWUE) (0.55 t ha⁻¹ cm⁻¹) was obtained by placing the drip lateral at 10 cm depth. The greater vertical movement of water in the sandy-loam soil took place because of the predominant role of gravity rather than that of the capillary forces. Therefore, placement of drip lateral at shallow depths is recommended in onion crop to get higher yield.     

滴灌土壤湿润体迁移计算的人工神经网络模型

基于非饱和土壤水分运动理论和单点源滴灌中土壤水分迁移特征,应用HYDRUS-2D/3D模型对33种土壤质地(分属11类土质类型,美国制土壤质地分类系统)、不同滴灌流量(1,2,3 L/h)下的湿润体运动过程进行了数值模拟,然后根据不同土壤质地和滴灌流量下湿润体动态变化的HYDRUS模拟结果,以滴灌量和土壤饱和导水率与滴灌流量的比值作为输入变量,构建了描述滴灌湿润体在不同土质和滴灌流量下迁移变化的人工神经网络模型.该模型输入变量少、易于操作,且将模型计算结果与实测情况对比表明,计算的入渗过程与实测的入渗过程基本一致,相关系数的平方(R²)均在0.82以上,因此该模型对不同土质中湿润体运移规律的预测效果较好.     

Tomato root distribution, yield and fruit quality under different subsurface drip irrigation regimes and depths

Tomato rooting patterns, yield and fruit quality were evaluated in a field trial where three irrigation regimes [0.6 (DI), 0.9 (DII) and 1.2 ET_c (DIII)] and three drip irrigation depths [surface (R0), subsurface at 20 cm depth (RI) and subsurface at 40 cm depth (RII)] were imposed following a split-plot experimental design, with four replications. The behaviour of the root system in response to the irrigation treatments was evaluated using minirhizotrons installed between two plants, near the plant row. Root-length intensity (L _a)—length of the root per unit of minirhizotron surface area (cm cm⁻²)—was measured at four crop stages. For all sampling dates, none of the factors studied were found to influence L _a or rooting depth significantly or the interaction between treatments. For all treatments most of the root system was concentrated in the top 40 cm of the soil profile, where the root-length density ranged from 0.5 cm cm⁻³ to 1.4 cm cm⁻³ . The response of tomato fruits to an increase in the water applied was similar in quantitative and qualitative terms for the different drip irrigation depths. Water applied by drip irrigation had the opposite effect on commercial yield (t ha⁻¹) and soluble solids (°Brix) (r=−0.82, P<0.001), however, yield in terms of total soluble solids (t ha⁻¹) was the same for the 0.9 and 1.2 ET_c. The increase in commercial yield can be described by the equation      

Soil water variability under subsurface drip and furrow irrigation

Non-uniformities in soil hydraulic properties and infiltration rates are considered to be major reasons for the inefficiencies of some surface irrigation systems. These non-uniformities may cause non-uniformities in soil water contents and could potentially affect plant growth. To investigate whether the non-uniformities in soil water contents can be overcome by well-managed irrigation systems, fields with clay loam soils and planted to cotton were irrigated with a continuous-flow, a surge flow, and a subsurface drip system. Measurements of water contents in each field were taken throughout the growing season at several depths. The water contents measured within the top 0–0.9 m in the three irrigations systems were evaluated in terms of their spatial and temporal variabilities. The analyses indicated that on this soil, use of the surge flow system did not lead to increased spatial uniformities of soil water contents compared with the continuous-flow system. Use of the subsurface drip system resulted in very non-uniform soil water contents above the depth of the emitters. Variability in water contents below the emitter depth was comparable to the surface irrigation systems. Received: 26 March 1996     

Using a subsurface drip irrigation system to measure crop water use

Procedures are presented for determining crop water use and crop coefficients for a row crop, using a neutron scattering probe with an efficient subsurface drip irrigation system. One procedure is called the slope-projection method, and the other is called a covariance procedure. Field tests were conducted with full-season, narrow-row cotton (Gossypium hirsutum L.) on a well-drained, sandy soil in a semiarid environment over a 5-year period. The goal was to improve automated irrigation scheduling, by relating evapotranspiration (ET) to growing degree days (GDD). The result, using a Penman–Monteith reference ET, was an average midseason crop coefficient of 1.11, with a standard error of 0.056. With class A pan evaporation as the reference ET, the average midseason crop coefficient was 0.877, with a standard error of 0.029. A fifth-order polynomial for the pan-based crop coefficient as a function of GDD was programmed into a controller and used successfully to irrigate a field automatically for one season.Communicated by A. Kassam     

Effects of drip irrigation frequency on soil wetting pattern and potato growth in North China Plain

The effect of irrigation frequency on soil water distribution, potato root distribution, potato tuber yield and water use efficiency was studied in 2001 and 2002 field experiments. Treatments consisted of six different drip irrigation frequencies: 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), with total drip irrigation water equal for the different frequencies. The results indicated that drip irrigation frequency did affect soil water distribution, depending on potato growing stage, soil depth and distance from the emitter. Under treatment N1, soil matric potential (ψ_m) Variations at depths of 70 and 90 cm showed a larger wetted soil range than was initially expected. Potato root growth was also affected by drip irrigation frequency to some extent: the higher the frequency, the higher was the root length density (RLD) in 0–60 cm soil layer and the lower was the root length density (RWD) in 0–10 cm soil layer. On the other hand, potato roots were not limited in wetted soil volume even when the crop was irrigated at the highest frequency. High frequency irrigation enhanced potato tuber growth and water use efficiency (WUE). Reducing irrigation frequency from N1 to N8 resulted in significant yield reductions by 33.4 and 29.1% in 2001 and 2002, respectively. For total ET, little difference was found among the different irrigation frequency treatments.     

Bell pepper response to surface and subsurface drip irrigation under different fertigation levels

A two-year field experiment was conducted in 2007 and 2008 to investigate different bell pepper responses to subsurface drip irrigation (SDI) and surface drip irrigation (DI) under four nitrogen levels: 0, 75, 150, and 300 kg/ha N (N₀, N₇₅, N₁₅₀, and N₃₀₀, respectively). Irrigation interval was set at 4 days. Bell pepper yield under SDI was significantly higher than that under DI by 4% in 2007 (13% in 2008). Water consumption under SDI was lower than that under DI by 6.7% in 2007 (7.3% in 2008). Meanwhile, root length density under SDI was obviously higher than that under DI by 11.8% in 2007 (12.5% in 2008). The percentage of root length below 10-cm soil depth under SDI was higher than that under DI by 7%, proving that SDI promotes crop root growth and enhances downward root development. Soil N residue under SDI was lesser than that under DI. Lastly, SDI with N application of 150 kg/ha is recommended as an optimal fertigation practice in improving bell pepper yield and water-use efficiency, as well as in NO₃ ⁻-N leaching.     

Managing subsurface drip irrigation in the presence of shallow ground water

A 3-year project compared the operation of a subsurface drip irrigation (SDI) and a furrow irrigation system in the presence of shallow saline ground water. We evaluated five types of drip irrigation tubing installed at a depth of 0.4 m with lateral spacings of 1.6 and 2 m on 2.4 ha plots of both cotton and tomato. Approximately 40% of the cotton water requirement and 10% of the tomato water requirement were obtained from shallow (<2 m) saline (5 dS/m) ground water. Yields of the drip-irrigated cotton improved during the 3-year study, while that of the furrow-irrigated cotton remained constant. Tomato yields were greater under drip than under furrow in both the years in which tomatoes were grown. Salt accumulation in the soil profile was managed through rainfall and pre-plant irrigation. Both drip tape and hard hose drip tubing are suitable for use in our subsurface drip system. Maximum shallow ground water use for cotton was obtained when the crop was irrigated only after a leaf water potential (LWP) of −1.4 MPa was reached. Drip irrigation was controlled automatically with a maximum application frequency of twice daily. Furrow irrigation was controlled by the calendar.     

滴灌玉米根系生长动态对灌水量响应的试验研究

通过连续2年的盆栽试验,设置100%ET_c,75%ET_c和50%ET_c(作物需水量)3个灌水水平,分析了滴灌不同灌水水平对土壤水分、根系生长动态分布的影响.结果表明,玉米根长密度随土壤深度和距滴头水平距离的增加均逐渐减小;玉米根长密度随着生育期的变化而变化,拔节期根长密度最小,抽穗灌浆期达到峰值,成熟期后期根长密度有所降低.拔节期各处理垂向根长密度差异较小,抽穗灌浆期处理75%ET_c0~40 cm土层根长密度分别比处理50%ET_c和100%ET_c高8%和26%;成熟期处理50%ET_c0~60 cm土层根长密度最大,分别比处理75%ET_c和100%ET_c高51%和40%.拔节期和灌浆期处理50%ET_c和75%ET_c水平方向根长密度均比处理100%ET_c高29%;成熟期处理50%ET_c水平方向根长密度最大,分别比处理75%ET_c和100%ET_c高52%和40%.     

Cotton yield and applied water relationships under drip irrigation

Different irrigation scheduling methods and amounts of water ranging from deficit to excessive amounts were used in cotton (Gossypium hirsutum L.) irrigation studies from 1988 to 1999, at Lubbock, TX. Irrigation scheduling treatments based on canopy temperature (T_c) were emphasized in each year. Surface drip irrigation and recommended production practices for the area were used. The objective was to use the 12-year database to estimate the effect of irrigation and growing season temperature on cotton yield. Yields in the irrigation studies were then compared with those for the northwest Texas production region. An irrigation input of 58 cm or total water application of 74 cm was estimated to produce maximum lint yield. Sources of the total water supply for the maximum yielding treatments for each year averaged 74% from irrigation and 26% from rain. Lint yield response to irrigation up to the point of maximum yield was approximated as 11.4 kg ha⁻¹ cm⁻¹ of irrigation between the limits of 5 and 54 cm with lint yields ranging from 855 to 1630 kg ha⁻¹. The intra-year maximum lint yield treatments were not limited by water input, and their inter-year range of 300 kg ha⁻¹ was not correlated with the quantity of irrigation. The maximum lint yields were linearly related to monthly and seasonal heat units (HU) with significant regressions for July (P=0.15), August (P=0.07), and from May to September (P=0.01). The fluctuation of maximum yearly lint yields and the response to HU in the irrigation studies were similar to the average yields in the surrounding production region. The rate of lint yield increase with HU was slightly higher in the irrigation studies than in the surrounding production area and was attributed to minimal water stress. Managing irrigation based on real-time measurements of T_c produced maximum cotton yields without applying excessive irrigation.     

玉米地下滴灌适宜出苗灌水定额试验研究

为探索解决地下滴灌玉米出苗难的问题,通过土箱试验,对内蒙古自治区具有典型代表性的3种土壤,开展了毛管铺设参数(滴头流量、埋深)和灌水定额对地下滴灌湿润半径的影响规律试验,结合玉米播种深度、水分向上及向下运移的距离及种子周围土壤含水量,研究了玉米适宜出苗灌水定额,以提高出苗率,指导实际生产.结果表明:按显著性水平0.05检验,土壤类型和灌水定额均对土壤湿润半径影响具有统计学意义,而滴头流量和埋深对湿润半径影响不具有统计学意义.在黏壤土中,玉米出苗灌水定额37.5~52.5 mm基本可满足毛管埋深25~35 cm的出苗要求;在壤土中,玉米出苗灌水定额37.5 mm左右基本可满足毛管埋深25~30 cm的出苗要求,灌水定额52.5 mm左右基本可满足埋深30~35 cm的出苗要求;在砂壤土中,灌水定额22.5~37.5 mm基本可满足毛管埋深约25 cm的玉米出苗要求,灌水定额52.5 mm基本可满足毛管埋深25~35 cm的玉米出苗要求.     

Effect of amount and timing of subsurface drip irrigation on corn yield

A field study was conducted at North Platte, Nebraska in 2007–2009, imposing eight irrigation treatments, ranging from dryland to fully irrigated. Four of the eight treatments allowed for various degrees of water stress only after tasseling and silking. In 2007, corn yield ranged from 8.9 Mg ha^?1 with a season total of 41 mm of irrigation water to 11.5 Mg ha^?1 for the fully irrigated treatment (264 mm of irrigation water). The treatment with the greatest reduction in irrigation water after tasseling and silking (158 mm) had a mean yield of 10.9 Mg ha^?1, only 0.6 Mg ha^?1 less than the fully irrigated treatment. In 2009, yields ranged from 12.6 to 13.5 Mg ha^?1. There were no significant yield differences between the irrigation treatments for several possible reasons: more in-season precipitation and cooler weather required less irrigation water; much of the irrigation water was applied after the most water-stress sensitive stages of tasseling and silking; and lower atmospheric demand allowed for soil water contents well below 50 % management allowed depletion (MAD) not to cause any yield losses.