Subsurface drip irrigation and reclaimed water quality effects on phosphorus and salinity distribution and forage production

In the Canary Islands, water scarcity is one of the constraints for agricultural activity. Non-conventional water resources generally represent more water volume than conventional ones. The distribution of these resources frequently permits the possibility of a conjunctive use of desalinated (DW) water and reclaimed municipal wastewater (RW). Field testing with both water qualities and different irrigation systems is necessary for optimal site-specific management. The objective of this work was to evaluate soil salinity and phosphorus distribution, and alfalfa yield in a 20 month field experiment carried out in the island of Gran Canaria, using municipal RW and freshwater (FW) under subsurface drip irrigation (SDI). Phosphorus speciation was performed both in irrigation waters and in soils (Olsen's inorganic, organic, and microbial). RW had large EC values (2.4 dS m⁻¹) with a remarkable nutrient load contribution and an average total P around 3 mg L⁻¹, predominantly hydrolysable forms, while FW had very low salinity and negligible amounts of P. For the RW treatment a salt gradient was established, causing plant mortality between the irrigation lines. The study of P speciation allows describing P distribution and plant uptake in terms of P forms. Large values of microbial P were produced for the two irrigation waters around the emitters, especially for FW.A faster P-cycling could have contributed to the significantly larger inorganic P contents observed in FW irrigated soils, in spite no external sources were added by the irrigation water.     

Yield, water-use efficiencies and root distribution of soybean, chickpea and pumpkin under different subsurface drip irrigation depths and oxygation treatments in vertisols

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUE_sl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.     

Emitter discharge variability of subsurface drip irrigation in uniform soils: effect on water-application uniformity

Emitter discharge of subsurface drip irrigation (SDI) decreases as a result of the overpressure in the soil water at the discharge orifice. In this paper, the variation in dripper discharge in SDI laterals is studied. First, the emitter coefficient of flow variation CV _q was measured in laboratory experiments with drippers of 2 and 4 L/h that were laid both on the soil and beneath it. Additionally, the soil pressure coefficient of variation CV _hs was measured in buried emitters. Then, the irrigation uniformity was simulated in SDI and surface irrigation laterals under the same operating conditions and uniform soils; sandy and loamy. CV _q was similar for the compensating models of both the surface and subsurface emitters. However, CV _q decreased for the 2-L/h non-compensating model in the loamy soil. This shows a possible self-regulation of non-compensating emitter discharge in SDI, due to the interaction between effects of emitter discharge and soil pressure. This resulted in the irrigation uniformity of SDI non-compensating emitters to be greater than surface drip irrigation. The uniformity with pressure-compensating emitters would be similar in both cases, provided the overpressures in SDI are less than or equal to the compensation range lower limit.     

地下滴灌灌水器出口正压试验研究

通过试验 ,研究了灌水器类型、流量、工作压力和土壤初始含水量对地下滴灌灌水器出口正压的影响规律。结果表明 :灌水器埋入土壤后 ,其出流由于受土壤等因素的限制 ,在灌水器出口处产生了一定的正压 ,该正压随着灌水历时的延长而增大。影响地埋灌水器出口正压的主要因素是灌水器的额定流量和土壤初始含水量     

覆膜和降雨强度对玉米耗水过程及土壤水分入渗的影响

【目的】研究农田作物生长过程中,覆膜和降雨特征等因素对玉米耗水过程和土壤入渗产生影响。【方法】根据北京地区典型年降雨量设计和模拟春玉米生育期降雨过程,利用群集式测坑和挡雨棚及附设人工降雨装置,开展了不同地表覆盖条件下降雨强度对玉米耗水及水分利用效率的影响研究。降雨强度包括小雨强0.5 mm/min和大雨强1.5 mm/min,覆盖和种植条件包括膜下滴灌(MDI)、地面滴灌(SDI)和对照无作物种植(NP)。【结果】①MDI处理水分利用效率较SDI处理高13.5%。与SDI处理相比,MDI处理作物耗水量减小了40.6 mm,覆膜主要提高20～60 cm土层储水量。②大雨强条件下土壤深层渗漏量增多了3.4%～15.6%;降雨和灌溉对土壤水分影响深度主要为0～150 cm土层,相对于SDI处理,MDI和NP处理土壤储水量大大增加。③小雨强时表层0～20cm土壤入渗NP处理最快,大雨强时MDI处理入渗最快。作物根区40 cm深度处,小雨强时MDI处理的土壤水分最快达到峰值,而大雨强时NP处理最快达到峰值。60 cm深度处不同覆盖条件下在2种雨强时土壤水分变化速率一致,达到峰值速率表现为NP处理>MDI处理>SDI处理。【结论】覆膜具有较好的节水增产效应;降雨强度越大,土壤水分下渗越快;相同降雨量时小雨强降雨更有利于土壤水存储。不同的降雨强度对土壤水分入渗和再分布影响不同。研究结果可为雨水资源的合理利用从而提高农田水分利用效率提供理论依据。     

Soil pits as a simple design aid for subsurface drip irrigation systems

A new method for designing subsurface drip irrigation (SDI) systems, referred to as the "soil pit method", is presented in this paper. The new method involves the installation of a trial irrigation system using thin-diameter polyethylene tube emitters. Soil water flow is then monitored by observation of the wetting front (WF) on the face of a soil pit. The soil pit method was applied at two field sites located at Forbes and Warren, New South Wales, Australia. Good agreement was found between the WF observed using the soil pit method and neutron moisture meter measurements of soil water content taken at both of the field sites. Data from the soil pit method was used to derive design parameters for drip irrigation systems at both field sites. These parameters were compared to those based on soil texture. At one site (Forbes), the two methods gave similar design parameters. A comparison of emitter lateral spacings that was conducted at this site confirmed that the lateral spacing suggested by the two methods was appropriate for the site. At the other site (Warren), however, the design parameters derived from the soil pit method were considerably different from those based on soil texture, with inadequate watering and water surfacing problems experienced from the SDI system designed using soil texture. Given the simplicity of the new design method and the minimal equipment and operator expertise that it requires, the soil pit method has potential to be a valuable tool in the design of SDI systems.Communicated by K. Bristow     

Tomato yield, biomass accumulation, root distribution and irrigation water use efficiency on a sandy soil, as affected by nitrogen rate and irrigation scheduling

Florida is the largest producer of fresh-market tomatoes in the United States. Production areas are typically intensively managed with high inputs of fertilizer and irrigation. The objectives of this 3-year field study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling on yield, irrigation water use efficiency (iWUE) and root distribution of tomato cultivated in a plastic mulched/drip irrigated production systems. Experimental treatments included three irrigation scheduling regimes and three N-rates (176, 220 and 230 kg ha⁻¹). Irrigation treatments included were: (1) SUR (surface drip irrigation) both irrigation and fertigation line placed right underneath the plastic mulch; (2) SDI (subsurface drip irrigation) where the irrigation line was placed 0.15 m below the fertigation line which was located on top of the bed; and (3) TIME (conventional control) with irrigation and fertigation lines placed as in SUR and irrigation being applied once a day. Except for the “TIME” treatment all irrigation treatments were controlled by soil moisture sensor (SMS)-based irrigation set at 10% volumetric water content which was allotted five irrigation windows daily and bypassed events if the soil water content exceeded the established threshold. Average marketable fruit yields were 28, 56 and 79 Mg ha⁻¹ for years 1-3, respectively. The SUR treatment required 15-51% less irrigation water when compared to TIME treatments, while the reductions in irrigation water use for SDI were 7-29%. Tomato yield was 11-80% higher for the SUR and SDI treatments than TIME where as N-rate did not affect yield. Root concentration was greatest in the vicinity of the irrigation and fertigation drip lines for all irrigation treatments. At the beginning of reproductive phase about 70-75% of the total root length density (RLD) was concentrated in the 0-15 cm soil layer while 15-20% of the roots were found in the 15-30 cm layer. Corresponding RLD distribution values during the reproductive phase were 68% and 22%, respectively. Root distribution in the soil profile thus appears to be mainly driven by development stage, soil moisture and nutrient availability. It is concluded that use of SDI and SMS-based systems consistently increased tomato yields while greatly improving irrigation water use efficiency and thereby reduced both irrigation water use and potential N leaching.     

Cost–benefit analysis of a regulated deficit-irrigated almond orchard under subsurface drip irrigation conditions in Southeastern Spain

A cost–benefit analysis was performed for a mature, commercial almond plantation [Prunus dulcis (Mill.) D.A. Webb] cv. Cartagenera in Southeastern Spain to determine the profitability of several regulated-deficit irrigation (RDI) strategies under subsurface drip irrigation conditions (SDI), compared to an irrigation regime covering 100% crop evapotranspiration (ETc). The plantation was subjected to three drip irrigation treatments for 4 years: T1 (control, surface drip irrigation)—irrigated at 100% ETc throughout the growth cycle, T2 (RDI treatment under SDI)—an irrigation strategy that provided 100% ETc except during the kernel-filling period, when only 20% ETc was provided and T3 (RDI treatment under SDI)—an irrigation strategy that provided 100% ETc except during the kernel-filling period (20% ETc) and post-harvest (50% ETc). A 45% water saving was achieved with strategy SDI T3, while almond production was reduced by only 17%, increasing water use efficiency compared to the control irrigation regime. SDI T3 had fixed overhead costs 9% higher than T1, however, the operating costs were 21% lower for SDI T3 compared to T1. This reduction in costs was basically due to the 45% saving in the cost of water and the corresponding saving in electricity. The break-even point was lower in SDI T3; each kilogram of almonds cost 0.03€ less to produce than in the control conditions. Related to this, the maximum price of water for obtaining profit 0 was 0.21€ m⁻³ for SDI T3 compared to 0.18€ m⁻³ for T1, indicating that higher water costs can be borne in SDI T3 (up to 0.03€ m⁻³ more expensive). Finally the profit/total costs ratio (used as an expression of the overall profitability of the orchard) indicated a greater profitability for the treatment SDI T3 compared to T1 (10.46 and 9.27%, respectively). The RDI strategy SDI T2 did not show economic indices or water use efficiency as much as those of SDI T3. From these results we conclude that RDI applied during kernel-filling and post-harvest under SDI conditions, and specifically the irrigation strategy SDI T3, may be considered economically appropriate in semiarid conditions in order to save water and improve water use efficiency.     

Subsurface drip irrigation of onions: Effects of drip tape emitter spacing on yield and quality

Improved irrigation water use efficiency is an important component of sustainable agricultural production. Efficient water delivery systems such as subsurface drip irrigation (SDI) can contribute immensely towards improving crop water use efficiency and conserving water. However, critical management considerations such as choice of SDI tube, emitter spacing and installation depth are necessary to attain improved irrigation efficiencies and production benefits. In this study, we evaluated the effects of subsurface drip tape emitter spacing (15, 20 and 30 cm) on yield and quality of sweet onions grown at two locations in South Texas—Weslaco and Los Ebanos. Season-long cumulative crop evapotranspiration (ETc) was 513 mm in Weslaco and 407 mm at Los Ebanos. Total crop water input (rain + irrigation) at Weslaco was roughly equal to ETc (92% ETc) whereas at Los Ebanos, water inputs exceeded ETc by about 35%. Onion yields ranged from 58.5 to 70.3 t ha⁻¹ but were not affected by drip tube emitter spacing. Onion pungency (pyruvic acid development) and soluble solids concentration were also not significantly influenced by treatments. Crop water use efficiency was slightly higher at Weslaco (13.7 kg/m³) than at Los Ebanos (11.7 kg/m³) partly because of differences in total water inputs resulting from differences in irrigation management. The absence of any significant effects of drip tape emitter spacing on onion yield may be due to the fact that irrigation was managed to provide roughly similar irrigation amounts and optimum soil moisture conditions in all treatments.     

Tomato nitrogen accumulation and fertilizer use efficiency on a sandy soil, as affected by nitrogen rate and irrigation scheduling

Tomato production systems in Florida are typically intensively managed with high inputs of fertilizer and irrigation and on sandy soils with low inherent water and nutrient retention capacities; potential nutrient leaching losses undermine the sustainability of such systems. The objectives of this 3-year field study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling on crop N and P accumulation, N-fertilizer use efficiency (NUE) and NO₃-N leaching of tomato cultivated in a plastic mulched/drip irrigated production system in sandy soils. Experimental treatments were a factorial combination of three irrigation scheduling regimes and three N-rates (176, 220, and 330 kg ha⁻¹). Irrigation treatments included were: (1) surface drip irrigation (SUR) both the irrigation and fertigation line placed underneath the plastic mulch; (2) subsurface drip irrigation (SDI) where the irrigation drip was placed 0.15 m below the fertigation line which was located on top of the bed; and (3) TIME (conventional control) with the irrigation and fertigation lines placed as in SUR and irrigation applied once a day. Except for the TIME treatment all irrigation treatments were soil moisture sensor (SMS)-based with irrigation occurring at 10% volumetric water content. Five irrigation windows were scheduled daily and events were bypassed if the soil water content exceeded the established threshold. The use of SMS-based irrigation systems significantly reduced irrigation water use, volume percolated, and nitrate leaching. Based on soil electrical conductivity (EC) readings, there was no interaction between irrigation and N-rate treatments on the movement of fertilizer solutes. Total plant N accumulation for SUR and SDI was 12-37% higher than TIME. Plant P accumulation was not affected by either irrigation or N-rate treatments. The nitrogen use efficiency for SUR and SDI was on the order of 37-45%, 56-61%, and 61-68% for 2005, 2006 and 2007, respectively and significantly higher than for the conventional control system (TIME). Moreover, at the intermediate N-rate SUR and SDI systems reduced NO₃-N leaching to 5 and 35 kg ha⁻¹, while at the highest N-rate corresponding values were 7 and 56 kg N ha⁻¹. Use of N application rates above 220 kg ha⁻¹ did not result in fruit and/or shoot biomass nor N accumulation benefits, but substantially increased NO₃-N leaching for the control treatment, as detected by EC monitoring and by the lysimeters. It is concluded that appropriate use of SDI and/or sensor-based irrigation systems can sustain high yields while reducing irrigation application as well as reducing NO₃-N leaching in low water holding capacity soils.     

不同灌溉方式对冬小麦生长发育及水分利用效率的影响

为了确定山西省晋南地区冬小麦高产高效的节水灌溉模式,采用田间小区试验,研究了微喷灌(MSI)、滴灌(SDI)和传统漫灌(CK)3种灌溉方式对冬小麦不同生育期的土壤水分变化、生长性状、产量和水分利用效率的影响。其中SDI处理和MSI处理生育期灌水3次,分别为越冬期(12月9日)、拔节期(4月1日)、灌浆期(5月20日),每次灌水量为600 m~3/hm~2;CK按当地灌水习惯,于越冬期和拔节期灌水,每次灌水量为2 250 m~3/hm~2。结果表明,各处理越冬期0~100 cm土层土壤含水率没有明显差异,灌浆期0~80 cm土层土壤含水率表现为SDI处理MSI处理CK,MSI处理、SDI处理灌浆期灌水,可满足灌浆期对水分需求,促进籽粒灌浆;与CK相比,SDI处理与MSI处理可以明显增加单株分蘖数和总茎数、促进群体生长,显著增加冬小麦成穗数、穗粒数和千粒质量,因而显著提高了籽粒产量。与CK相比,MSI处理穗粒数、千粒质量分别提高16.54%、5.21%,SDI处理穗粒数、千粒质量分别提高9.10%、11.78%,MSI、SDI处理籽粒产量分别增加了2.79%、3.35%;同时,SDI处理与MSI处理冬小麦生育期的耗水总量分别减少43.88%和41.64%,水分利用效率分别提高了83.15%和77.09%。因此,在山西临汾盆地采用微喷与滴灌可以取得明显的节水高产效果。     

基于TOPSIS方法的喀斯特断陷盆地区番茄地下灌溉技术节水效益综合评价

喀斯特断陷盆地区季节性干旱严重,水资源匮乏,高效节水灌溉是解决该区域水资源不足的重要途径.采用膜下滴灌、渗灌、地下滴灌和分根区交替地下滴灌4种节水灌溉方式对该区域广泛种植的蔬菜番茄进行试验,设置不同的灌水下限处理(分别为田间持水量的55％～65％,65％～75％和75％～85％),利用TOPSIS法对番茄品质、产量和灌...     

Effects of alternative water distribution rules on irrigation system performance: a simulation analysis

Based on a simulation model reflecting physical and economic conditions typically found in rice irrigation systems in Asia, the irrigation performance implications of alternative water distribution rules for dry season irrigation are evaluated under varying degrees of water shortage. The rules examined reflect differing water distribution strategies designed either to maximize conveyance efficiency, economic efficiency, or equity; or to achieve a balance between efficiency and equity objectives. Irrigation performance is evaluated using several efficiency measures reflecting the physical, agronomic and economic productivity of water, and one measure of equity. Economic efficiency and equity among farmers within the portion of the irrigation system that is on in any given season are shown to be complementary, and not competing objectives. Economic efficiency and equity among all farmers within the command area of the irrigation system are largely complementary strategies at the lower levels of water shortage, but with increasing shortage, significant tradeoffs develop between these objectives. An operational rule for water distribution under a goal of maximizing economic efficiency is developed, and the data requirements for its implementation are shown to be modest. Under the model's assumed conditions of dry season rice production dependent solely on surface irrigation for water, the distribution strategy designed to maximize conveyance efficiency results in only modestly lower levels of economic efficiency and equity than could be achieved by the strategy designed to maximize economic efficiency.     

Subsurface drip irrigation of corn in the United States Mid-South

Although rainfall in the United States Mid-South is sufficient to produce corn (Zea mays L.) without irrigation in most years, timely irrigation has been shown to increase yields. The recent interest in ethanol fuels is expected to lead to increases in US corn production, and subsurface drip irrigation (SDI) is one possible way to increase application efficiency and thereby reduce water use. The objective of this study was to determine the response of SDI-irrigated corn produced in the US Mid-South. Field studies were conducted at the University of Arkansas Northeast Research and Extension Center at Keiser during the 2002-2004 growing seasons. The soil was mixed, with areas of fine sandy loam, loamy sand, and silty clay. SDI tubing was placed under every row at a depth of approximately 30 cm. Three irrigation levels were compared, with irrigation replacing 100% and 60% of estimated daily water use and no irrigations. The split plot treatment was hybrid, with three hybrids of different relative maturities. Although the 3-year means indicated significantly lower yields for a nonirrigated treatment, no significant differences were observed among the treatments in 2003 or 2004. A large difference was observed in 2002, the year with the least rainfall during the study period, but no difference was detected between the two irrigated treatments in any year. The treatment with the lower water application had the higher irrigation water use efficiency. Although the results of this study suggested that replacing 60% of the estimated daily evapotranspiration with SDI is sufficient for maximum corn yields, additional observations will be needed to determine whether corn production with SDI is feasible in the region and to develop recommendations for farmers choosing to adopt the method. Improved weather forecasting and crop coefficient functions developed specifically for the region should also contribute to more efficient irrigation management.     

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.     

Soil water content on drip irrigated cotton: comparison of measured and simulated values obtained with the Hydrus 2-D model

Crop irrigation with subsurface drip (SDI) is increasing in the semiarid Texas High Plains (THP). Information on drip-tubing positioning, irrigation strategies, and wetted soil area is needed to increase rainwater effectiveness when well capacities are inadequate to meet full irrigation requirements. Time and resources necessary to test SDI strategies for different conditions through field experimentation is too large. However, a mechanistic model such as Hydrus-2D can quantify the effect of different installation geometries and irrigation strategies. Our objective was to experimentally validate the Hydrus-2D in an Amarillo soil in THP so that the model can be used to evaluate different irrigation frequency and timing strategies for SDI cotton. Results showed that Hydrus-2D simulated volumetric soil water content within ±3% of measured values, and simulation bias represented the smaller portion of the simulation error, indicating that the model can be used to evaluate irrigation strategies.     

Subsurface drip irrigation for corn production: a review of 10 years of research in Kansas

Kansas State University initiated studies in 1989 to develop the methodology for successful application of subsurface drip irrigation (SDI) for corn production on the deep silt loam soils of the Central Great Plains, USA. Irrigation water use for corn can be reduced by 35–55% when using SDI compared with more traditional forms of irrigation in the region. Irrigation frequency has not been a critical issue when SDI is used for corn production on the deep silt loam soils of the region. A dripline spacing of 1.5 m has been found to be most economical for corn grown in 0.76 m spaced rows. Nitrogen fertigation was a very effective management tool with SDI, helping to maximize corn grain yield, while obtaining high efficiencies of nitrogen and water use. The research SDI systems have been utilized since 1989 without replacement or major degradation. SDI systems lasting 10–20 years are cost competitive for corn production with the more traditional forms of irrigation in the Great Plains for certain field sizes.Communicated by P. Thorburn     

再生水高效安全灌溉关键理论与技术研究进展

再生水灌溉已成为世界范围内缓解水资源供需矛盾的有效手段。再生水中含有一定量的有害物质可能带来农田生态环境的污染风险,不合理再生水灌溉引起的系统安全和环境污染风险成为限制其应用的主要因素。以实现系统稳定、环境持续和调控有效为目标,深入开展相关理论和技术问题研究是保证再生水高效安全灌溉的关键。在系统总结国内外研究成果的基础上,分析了再生水灌溉对灌水器、灌溉系统、农田环境以及农产品等不同尺度介质的影响,阐释了再生水中的养分、盐分、微生物和典型污染物等的行为特征及相互作用机制。提出需要进一步研究再生水灌溉对系统性能影响的微观机制与宏观特征、对环境影响的动力学过程、对养分吸收利用及转化过程的影响以及高效安全调控机制等关键理论和技术,为实现再生水的高效安全灌溉提供参考。     

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     

Effective irrigation uniformity as related to root zone depth

Summary In models used for relating the yield to irrigation uniformity it has been assumed that the spatial distribution of irrigation water, as measured at the soil surface, is indeed the water distribution at any depth throughout the root zone. In the present paper the distribution of infiltrated water within the soil bulk, as determined by an analytic solution of the two-dimensional unsaturated flow equation, did not conform to this assumption. A new alternative definition of irrigation uniformity is proposed under the assumption that water uptake by roots does not affect the flux distribution within the soil profile. In this analysis the spatial distribution of irrigation water flux at the soil surface, which is the upper boundary condition of the flow equation, is assumed to be a sine function. The solution to this problem indicates that there is a damping effect, which increases with soil depth, on the surface flux fluctuations. Furthermore, the actual irrigation uniformity at a given depth below the soil surface depends upon the initial uniformity at the surface and the distance between adjacent water sources. The closer the water sources are to each other, the shallower is the depth needed to damp the oscillations down to a certain level. This may explain why the actual uniformity of drip irrigation is high while the detailed distribution is very nonuniform and on the other hand, why the actual uniformity of sprinkler guns is low while the detailed actual distribution is close to uniform. Two uniformity coefficients are derived in this study: 1. A depth dependent coefficient which is made up of the damping factor that multiplies the flux fluctuations at the soil surface; 2. An effective uniformity coefficient, which is an average of the depth dependent coefficient over a part or the entire root zone. Different degrees of uniformity are expected when water is applied by different irrigation systems having similar uniformity coefficients at the soil surface, but dissimilar distances between the emitters. Assuming that crop yield depends to some extent on the uniformity of water depth actually available to the roots, the yields associated with such irrigation systems will probably also vary.