Effects of wastewater irrigation on soil sodicity and nutrient leaching in calcareous soils

Soil column studies were conducted with two soils to assess the effects of irrigation with wastewater on soil and groundwater quality. Upon the application of wastewater, exchange occurred between solution sodium (Na⁺) and exchangeable cations (Ca²⁺, Mg²⁺, K⁺), whereby these cations were released into solution. The average exchangeable sodium percentage (ESP) of the soils increased during leaching from 9 to 21 and 28.8 to 29.7 after applying 5.0 and 3.5 l (about 7 and 6 pore volumes) of wastewater to the soils columns, respectively. Adverse effect of high Na⁺ concentration in the wastewater on raising ESP was less pronounced in the soil having initial high ESP than in the soil with low initial ESP. Salinity of the soils was also increased with the application of wastewater and Mg²⁺ and K⁺ were leached from the soils. These losses would be more severe on soils having a low cation exchange capacity and if, uncorrected could lead eventually to their deficiencies for plant growth. When the soil columns were leached with distilled water the flow rate of one soil decreased to zero after 2.2 pore volume indicating damage to soil structure. Irrigation with wastewater, which is generally more sodic and saline than regional groundwater, increases the rate of soil sodification of shallow groundwater. A relatively simple chromatographic model was used to estimate final ESP profiles in the soils assuming the condition of local equilibrium. This approach had a limited success for one of the soil. Since the final leached concentrations are in good agreement with those of wastewater, we attribute these differences to non-uniform flow through the column. In terms of practical soil and water management, our study reveals that relatively simple means can be useful to predict the water quality in soils, their discharge to ground water, and the hazard of soil structure deterioration.     

Use of treated municipal wastewater in irrigated agriculture—Review of some practices in Spain and Greece

Approximately, seventy (70) percent of world water use including all the water diverted from rivers and pumped from underground is used for agricultural irrigation, so that the reuse of treated municipal wastewater for purposes such as agricultural and landscape irrigation reduces the amount of water that needs to be extracted from natural water sources as well as reducing discharge of wastewater to the environment. Thus, treated municipal wastewater is a valuable water source for recycling and reuse in the Mediterranean countries and other arid and semi-arid regions which are confronting increasing water shortages. Treated wastewater reuse in agriculture is a common practice in the Mediterranean countries and there is a considerable interest in the long-term effects of treated wastewater on crops intended for human consumption. This paper reviews the fundamentals of agricultural irrigation using treated municipal wastewater and the status of municipal wastewater reuse in Greece and Spain with studies related to the effects on soils and plants.     

Can irrigation be sustainable?

Globally, about 10 Mha of agricultural land is lost annually due to salinisation, of which about 1.5 Mha is in irrigated areas. While some climate and management aspects are common to semi-arid regions, the detailed mechanisms and options to secure ecological sustainability and economic viability may vary considerably from case to case. This paper applies a whole of system-water balance to compare irrigation in three semi-arid regions suffering from similar sustainability issues: Rechna Doab (RD), Pakistan; the Liuyuankou irrigation system (LIS), China; and Murrumbidgee irrigation area (MIA), Australia. Soil salinity, lack of adequate water resources and groundwater management are major issues in these areas. The MIA and LIS irrigation systems also suffer from soil salinity and low water-use efficiency issues. These similarities occur in spite of very different climatic and underlying hydrogeological conditions. The key data used to compare these different regions are climate and soils, available water resources and their use, as well as components of the water balance. In addition, the history of water resource development in these areas is examined to understand how salinity problems emerge in semi-arid regions and the consequences for production. Based on the efficiency parameters and the definitions of sustainability, approaches are explored to solve common environmental problems while maintaining economic viability and environmental sustainability for irrigation systems.     

Measured and simulated soil wetting patterns under porous clay pipe sub-surface irrigation

Sub-surface irrigation with porous clay pipe can be an efficient, water saving method of irrigation for many less developed arid and semi-arid regions. Maximizing the efficiency of clay pipe irrigation requires guidelines and criteria for system design and operation. In this study, experimental and simulated (with HYDRUS (2D/3D)) soil wetting patterns were investigated for sub-surface pipe systems operating at different water pressures. Predictions of the soil water content made with HYDRUS were found to be in good agreement (R² = 0.98) with the observed data. Additional simulations with HYDRUS were used to study the effects of various design parameters on soil wetting. Increasing the system pressure increased the size of the wetted zone. The installation depth affects the recommended lateral spacing as well as the amount of evaporative water loss. For a given water application, the potential rate of surface evaporation affected the shape of the wetted region only minimally. Soil texture, due to its connection to soil hydraulic conductivity and water retention, has a larger impact on the wetting geometry. In general, greater horizontal spreading occurs in fine texture soils, or in the case of layered soils, in the finer textured layers.     

Planning and management modeling for treated wastewater usage

Due to urban growth, some agricultural lands have been replaced by residential, municipal, and industrial areas. In some cases the remaining agricultural land will not have enough water because of transfers from agriculture to M&I (municipal and industrial) users. Therefore, in many places, especially in arid and semi-arid regions, the use of treated wastewater as a reliable source of irrigation water has already been, or will be, considered in the future. Due to its unique characteristics, this new resource has many challenges that cannot be ignored, such as health issues, water quality, and long- and short-term effects on soils and crops. The study described herein considered the development of a new GIS-based model for planning and managing the reuse of treated wastewater for the irrigation of agricultural and green lands, considering various factors such as population and urban growth. The model is composed of several different modules, including an urban growth model. These modules are designed to help in the decision-making process for allocations of water resources to agricultural areas, considering factors such as crop types, crop pattern, water salinity, soil characteristics, pumping and conveyance costs, and also by comparing different management scenarios. Appropriate crops that can be grown with a specific water salinity and soil characteristics, proper water resources for each farm (according to pumping and conveyance costs, and analysis of water demand, and water supply) can be determined through the application of this model. The model can also rank agricultural areas and open spaces in and near an urban area according to their suitability for irrigated agriculture.     

Evaluating salinity distribution in soil irrigated with saline water in arid regions of northwest China

In arid and semi-arid regions, salinity is a serious and chronic problem for agriculture. A 3-year field experiment in the arid environment of Xinjiang, northwest China, was conducted to study the salinity change in soil resulting from deficit irrigation of cotton with non-saline, moderate saline and high saline water. The salinity profile distribution was also evaluated by an integrated water, salinity, and nitrogen model, ENVIRO-GRO. The simulated and observed salinity distributions matched well. Results indicated that after 3 years of cotton production, the average salinity in the 1.0-m soil profile was 336% and 547% of the original soil profile, respectively, for moderate saline and high saline water irrigation. If the practices continued, the average soil salinity (EC_e) in the 1.0-m soil profile would approach a steady level of 1.7, 10.8, and 14.7 dS m⁻¹, respectively, for the treatments receiving irrigation waters of 0.33, 3.62, and 6.71 dS m⁻¹. It was concluded that deficit irrigation of saline water in this region was not sustainable. Model simulation showed that a big flood irrigation after harvest can significantly reduce the salt accumulation in the soil profile, and that this practice was much more efficient for salinity control than applying the same extra amount of water during the growing season.     

再生水灌溉对土壤盐分和重金属累积分布影响的研究

再生水是农业灌溉的重要水资源。为了合理利用城市污水处理后的再生水资源,采用天津市纪庄子污水处理厂二级出水作为再生水,以自来水为对照进行叶类蔬菜小区种植试验,研究了再生水灌溉对菜地土壤次生盐渍化及盐分离子和重金属离子累积分布规律的影响。结果表明:除0~15 cm土层全盐量增加外,15~45 cm土壤层盐分累积现象与自来水灌溉相比无明显差异。与自来水灌溉相比,短期内采用再生水灌溉不会显著增加土壤阳离子含量。重金属在土壤中的累积也不明显,同时,不同再生水灌溉水量条件下,土壤中重金属含量无显著差异,且土壤中的重金属含量都远低于国家标准规定的允许值,表明再生水短期灌溉对土壤环境不会造成污染影响。     

Supplemental irrigation of wheat with saline water

In arid and semi-arid regions, both rainfall and surface irrigation water supplies are unreliable and inadequate to meet crop water requirement. Groundwater in these regions is mainly marginally saline (2-6 dS/m) to saline (>6 dS/m) and could be exploited to meet crop water requirement if no adverse effects on crops and land resource occur. The fear of adverse effects has often restricted the exploitation of naturally occurring saline water. The results reveal that substituting a part or all except pre-sowing irrigation with saline water having an electrical conductivity (EC_iw) of 8 dS/m is possible for cultivation of wheat. Similarly, saline water with EC_iw ranging between 8 and 12 dS/m could be used to supplement at least two irrigations to obtain 90% or more of the optimum yield. In low rainfall years, the use of such waters for all irrigations, except pre-sowing, produced more yield than skipping irrigations. Apparently, even at this level of osmotic salt stress, matric stress is more harmful. Thus, it would be interesting to use such waters for wheat production in monsoon climatic regions.     

Effects of untreated and treated wastewater irrigation on some chemical properties of cauliflower (Brassica olerecea L. var. botrytis) and red cabbage (Brassica olerecea L. var. rubra) grown on calcareous soil in Turkey

The use of wastewater for irrigation is increasingly being considered as a technical solution to minimize soil degradation and to restore nutrient content of soils. The aims of this study were to test if wastewater irrigation could improve soil fertility without affecting the quality of soils and plants. A field experiment was conducted in 2006 to investigate the effects of irrigation with untreated, and preliminary and primary treated wastewater on macro- and micronutrient distribution within the soil profile, yield and mineral content of cauliflower and red cabbage plants grown on a calcareous Aridisol in eastern Anatolia, Erzurum province, Turkey. Wastewater irrigation affected significantly soil chemical properties in the 0–30 cm soil layer and plant nutrient content after harvest. Application of wastewater increased soil salinity, organic matter, exchangeable Na, K, Ca, Mg, plant available phosphorus and microelements, and decreased soil pH. Wastewater irrigation treatments also increased the yield as well as N, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, Pb, Ni and Cd contents of cauliflower and red cabbage plants. The highest yield, macro- and micronutrient uptake of cauliflower and red cabbage plants were obtained with the untreated wastewater. Undesirable side effects such as heavy metal contamination in soil and plant, and salinity were not observed with the application of wastewater. It can be concluded that untreated wastewater can be used confidently, in the short term, in agricultural land, while primary treated wastewater can be used in sustainable agriculture in the long term.     

Avocado root distribution in fine and coarse-textured soils under drip and microsprinkler irrigation

A common irrigation-scheduling problem in orchards is the proper location of instruments for monitoring soil water content within the active root zone. Given the high spatial variability of soils in the field, and seasonal changes in root distribution and frequency, both within the orchard and around the trees, the accuracy and representativeness of soil water measurements can be strongly affected. Adequate soil water monitoring in orchards thus requires assessment of the variability and location of the active roots in a given location over an extended period of time. We examined the root systems of 12-year-old ‘Hass’ avocado (Persea americana Mill.) trees grafted on ‘Mexicola’ seedling rootstocks, growing in fine or coarse-textured soils, under either drip or microsprinkler irrigation systems in Central Chile. We dug 3 m long and 0.75 m deep trenches within the tree rows in spring, summer and autumn, and counted the active roots (white, diameter ≤2 mm) found on the walls. Over the three growing seasons of our study, season had the most significant effect on root distribution, as autumn root frequencies accounted for about half of the cumulative average. Also, the location of the highest concentration of roots under microsprinklers in autumn clearly differed between the fine soils, at about 200 cm from the trunk and 50–60 cm deep, and coarse soils, where they were found within 30 cm from the trunk, and within the first 25 cm of soil. Trees in fine soil had 25% more roots than those in coarse soil, and drip irrigation produced about 30% more roots than microsprinkler, although both of these figures are mainly due to the high number of roots found in the fine soil-drip irrigation combination. Overall, we found the highest root frequency within the first meter from the tree trunk, for all combinations, with some differences between irrigation types. Throughout the growing season in semi-arid regions, some changes in both the quantity of tree roots and the location of the zones of the greatest root activity should be expected, which will vary according to the seasonal soil temperatures, soil texture, and type of irrigation used.     

Field-scale assessment of deep drainage risk

Improving irrigation efficiency is of primary importance in arid and semi-arid regions of the world as a consequence of increasing incidences of soil and water salinisation. In the cotton-growing regions of Australia salinisation is generally a result of inefficient irrigation practices, which lead to excessive deep drainage (DD). There is therefore the need to apply a relatively inexpensive approach to assessing where inefficiencies occur and make prediction of suitability of existing and new water storage sites. However, physical methods of measuring DD, such as flux meters and lysimeters, are time-consuming and site-specific. In this paper we apply a rapid method for determining the spatial distribution of soil in an irrigated cotton field in the lower Gwydir valley. First, EC_a data (using EM38 and EM31) were used to determine a soil-sampling scheme for determining soil information such as clay content and exchangeable cations to a depth of 1.2 m. The soil data and water quality information were input into the SaLF (salt and leaching fraction) model to estimate DD rate (mm/year). In developing the relationship between EC_a and estimated DD, three exponential models (two-, three- and four-parameter) were compared and evaluated using the Aikakie information criteria (AIC). The three-parameter exponential model was found to be best and was used for further analysis. Using the geostatistical approach of multiple indicator kriging (MIK), maps of conditional probability of DD exceeding a critical cut-off value (i.e. 50, 75, 100 mm) were produced for various rates of irrigation (I=300, 600, 1,200 and 1,500 mm/year). The areas of highest risk were consistent with where water-use efficiency was problematic and thus leading to the creation of perched water tables. The advantage of this approach is that it is quick and is applicable to situations where efficient use of water is required. The results can be used for irrigation planning, particularly in the location of large irrigation infrastructure such as water reservoirs.     

非充分灌溉对冬小麦产量及水分利用效率影响研究

通过田间试验,研究冬小麦在不同生育期缺水以及不同程度的缺水对其生长发育及产量的影响,为半干旱区冬小麦建立优化灌溉制度提供理论依据。通过试验观测:枯水年份,冬小麦各生育期耗水比例相差较大,0~80cm土层的耗水量占总耗水量的绝大部分,总耗水量随灌水量的增加而增大,非充分灌溉对冬小麦叶面积、产量和水分利用率均会产生显著影响,灌水可显著提高植株叶面积,不灌水会显著降低作物产量与耗水量;灌1水的灌溉水利用效率明显高于灌2水和灌3水的灌溉水利用效率,其中以T2处理的灌溉水利用效率最高,边际效益最大;灌冬浇水与拔节水可获得较理想的产量和水分利用效率,在半干旱区水资源不足时,可作为冬小麦最佳灌水模式。     

喷灌技术在干旱风沙区的应用研究

喷灌在灌溉技术中具有独特的优势而得到广泛的应用,但因其受风的影响大、蒸发损失多,在风沙区的应用受到了极大的制约。通过对风沙区蒸发和风速分布规律的分析以及风沙区喷灌灌溉试验和喷灌在大田中应用的案例调查,给出了喷灌灌溉水利用效率与风速之间的关系,指出只要很好的利用风沙区蒸发和风速分布规律,避开高蒸发时段和高风速时区,在风沙区进行喷灌仍可获得较高的灌溉水利用效率和灌水均匀度,喷灌在风沙区仍有广阔的应用是前景。     

Sustainable and effective irrigation through a new subsoil irrigation system (SIS)

Since scarcity of water is a major problem in semi-arid and arid areas of Spain and many other Mediterranean regions, water consumption in irrigated agriculture has to be reduced to a sustainable level that is also adapted to the environment. This goal can be reached by applying the highly effective and resource preserving techniques of micro-irrigation. In order to improve these techniques, a new subsurface irrigation system was developed by modification of conventional subsurface systems through the following innovative elements:

a new design of the lateral hoses which prevents the penetration of roots into the external water outlets and the block up by soil particles;

an impermeable polyethylene foil placed below the lateral pipes to prevent water loss through deep percolation, especially in sandy substrates;

a special installation equipment consisting of a V-shaped device which releases foil and pipe simultaneously into the soil without disturbing the natural soil profile.

After the experience of several years of operation, these elements have proved to be highly effective. Compared to other irrigation methods, the high irrigation efficiency achieved by this system was outstanding. Minimum maintenance requirement and a long life span are additional positive characteristics of the system. The beneficial outcomes of this system give reason for an optimistic appraisal of the strategies involved towards sustainable irrigated agriculture.     

Could deficit irrigation be a sustainable practice for quinoa (Chenopodium quinoa Willd.) in the Southern Bolivian Altiplano?

The application of deficit irrigation (DI) to stabilize yield and to increase water productivity of quinoa (Chenopodium quinoa Willd.) raises questions in the arid Southern Altiplano of Bolivia where water resources are limited and often saline. Rainfed quinoa and quinoa with irrigation restricted to the flowering and early grain filling were studied during the growing seasons of 2005–2006 and 2006–2007 in a location with (Irpani) and without (Mejillones) water contribution from a shallow water table. It was found that the effect of additional irrigation was only significant above a basic fulfillment of crop water requirements of around 55%. Below this threshold, yields, total water use efficiency (TWUE) and marginal irrigation water use efficiency (MIWUE) of quinoa with DI were low. Capillary rise (CR) from groundwater was assessed using the one-dimensional UPFLOW model. The contribution of water from capillary rise in the region of Irpani ranges from 8 to 25% of seasonal crop evapotranspiration (ET_c) of quinoa, depending mostly on the depth of the groundwater table and the amount of rainfall during the rainy season. DI with poor quality water and cultivation of crops in fields with a shallow saline groundwater table pose a serious threat for sustainable quinoa farming. To assess the impact of saline water resources, soil salinity and required leaching were simulated by combining the soil water and salt balance model BUDGET with UPFLOW. The results indicate that irrigation of quinoa with saline water and/or CR from a saline shallow water table might, already after 1 year, result in significant salt accumulation in the root zone in the arid Southern Altiplano. A farming system with only 1 year fallow is often insufficient to leach sufficient salts out of the root zone. In case the number of fallow years cannot be increased, leaching by means of an important irrigation application before sowing is an alternative. Although potentially beneficial, DI of quinoa in arid regions such as the Southern Bolivian Altiplano should be considered with precaution.     

Use of saline–sodic waters through phytoremediation of calcareous saline–sodic soils

Use of poor-quality groundwater has become inevitable for irrigation to compensate rapidly increasing water demands in many arid and semiarid regions. Salinity and sodicity are the principal soil and water quality concerns in such areas. Many saline–sodic and sodic soils have saline or saline–sodic subsurface drainage waters. Amelioration of these soils needs a source of calcium (Ca²⁺) that can replace the excess exchangeable sodium (Na⁺). Most of these soils, however, contain calcite (CaCO₃) of extremely low solubility. The native calcite does not supply adequate levels of Ca²⁺ for soil amelioration as do other chemical amendments. Phytoremediation may help ameliorate such soils through cultivation of certain crops tolerant to ambient soil salinity and sodicity. This amelioration strategy works through plant root action to help dissolve CaCO₃ to supply adequate Ca²⁺ without the application of an amendment. During a 3-year field experiment conducted under irrigated conditions, we evaluated phytoremediation against soil application of gypsum and farm manure, and water treatment with sulphuric acid on a calcareous saline–sodic soil (pH_s=8.0–8.4, EC_e=24–32 dS m⁻¹, SAR=57–78, CaCO₃=45–50 g kg⁻¹ for the top 0.15 m depth; Calcic Haplosalids). A saline–sodic water (EC=2.9–3.4 dS m⁻¹, SAR=12.0–19.4, RSC=4.6–10.0 mmol_c l⁻¹, SAR_adj=15.6–18.4) was used to irrigate the rice (Oryza sativa L.) and wheat (Triticum aestivum L.) crops grown in rotation. Active desalinisation and desodication processes were observed in all the treatments. After the final wheat crop, the 1.2 m soil profile EC_e was 7±0.5 dS m⁻¹ and SAR was 15±2 with non-significant treatment differences, indicating comparable soil amelioration effect of phytoremediation with other treatments. Better crop yields were obtained from the manure-treated plots, owing to its annual addition to the soil that possibly improved soil fertility. Phytoremediation needed minimum capital input because no initial investment was made to purchase the amendments.     

Residual alkalinity as tracer to estimate the changes induced by forage cultivation in a non-saline irrigated sodic soil

Soil alkalinisation generally constitutes a major threat to irrigated agriculture in the semi-arid regions of west Africa. The improvement of sodic soils is generally difficult and expensive. However, a recent study in the Niger valley in Niger, reveals that a natural de-alkalinisation is possible under natural conditions in a semi-arid climate. Transformation of non-saline sodic soil into brown steppe soil type was recorded. On the same site, the cultivation of a Sahelian fodder grass, locally known as ‘Burgu’ was used on the sodic soil/brown steppe soil transition zone to accelerate this natural de-alkalinisation and characterise its mechanisms. The geochemical properties of both soil types were monitored before cultivation and 1 year after continuous crop cultivation. After cultivation and regular irrigation, the chemical properties of the former sodic soils were close to those of the surrounding brown steppe soils, which are better suited for agriculture. This modification of the sodic soil properties can be attributed to (i) the large amount of water supplied during cultivation that induced salt leaching. This is the main phenomenon responsible for the changes observed; (ii) the root activity that modified the acid–base equilibrium and consumes alkalinity.

The residual alkalinity (RA) concept was used to select chemical tracers of the concentration/dilution of the soil solution. Here, sodium amount and calcite+fluorite residual alkalinity (RA_{calcite+fluorite}) were the most adequate ones. These two tracers decreased proportionally under the influence of leaching, but the exchanges between cations and protons changed the RA_{calcite+fluorite}, without modifying the sodium amount. Their combined use allowed us to separate and quantify the uptake of the plant from the leaching in the de-alkalinisation process. This study highlighted that reclamation of this type of sodic soils is feasible. The use of the RA concept is advisable to design a sustainable management system for irrigated sodic or saline soils.     

长期喷灌条件下土壤剖面理化特性的变化研究

基于不同灌溉类型区土壤剖面理化性质的取样分析,对喷灌区、纯井灌区、河灌区及非灌溉区2m深度土壤剖面的理化性质进行了比较分析,揭示了长期喷灌条件下的土壤剖面理化性质的变化特征。结果表明,喷灌区与其他灌溉类型区相比,全剖面,尤其是心土层和底土层的含水率有较大幅度降低;犁底层及其以下一定深度范围内土层的干密度有较大幅度的增加...     

干旱区大田膜下滴灌对土壤盐分的影响

为研究干旱区大田膜下滴灌土壤盐分运移特征,在新疆石河子炮台试验站进行连续4年的试验研究。结果表明,膜下滴灌条件下,边行盐分偏高,棵间土壤盐分上升;耕作层土壤盐分下降,耕作层以下则增加,但由于滴灌灌水频繁,作物根系分布层内(0～40cm)土壤盐分始终处于较低值;利用膜下滴灌可以明显降低盐荒地土壤盐分,加速盐荒地改良和弃耕地的收复。     

Field comparison and crop production modeling of sweet corn and silage maize (Zea mays L.) with treated urban wastewater and freshwater

In Australia, interest in wastewater reuse has grown. While wastewater can potentially offer a nutrient advantage over conventional irrigation, crop yield increases may be offset by effects of high salinity. Effects of wastewater irrigation on crop production and soil health were investigated in two ways: a field experiment addressing short-term effects and modeling longer-term impacts. The field experiment was established at the Shepparton Wastewater Treatment Plant in Shepparton, Victoria, to compare effects of wastewater irrigation to conventional irrigation. Silage maize and sweet corn (Zea mays L.) were grown over the summer of 2012–2013 under the following flood irrigation treatments: wastewater and freshwater with and without fertilizer. Both harvests produced yields and qualities comparable to commercial farm standards, and no significant differences were found between water types. Maize production with long-term wastewater irrigation at various salinities was modeled, and no significant yield losses were observed after 50 years of simulated irrigation. Topsoil electroconductivity doubled after the field trial and simulation results predicted significant soil salt accumulation by factor of 2. Mean wastewater sodium absorption ratio of 4.52 and electroconductivity of 1.52 dS/m indicate potential for sodicity-related soil problems for long-term irrigation. Management of soil health may be necessary.