Replacing saline–sodic irrigation water with treated wastewater: effects on saturated hydraulic conductivity,slaking, and swelling

Irrigation with saline–sodic water imposes sodic conditions on the soil and reduces the soil’s productivity. We hypothesized that replacing saline–sodic irrigation water with lesser saline–sodic treated waste water (TWW), albeit with higher loads of organic matter and suspended solids, might help sodic soils regain their structure and hydraulic conductivity. We studied hydraulic conductivity (HC), aggregate stability and clay swelling of a soil from the Bet She’an Valley, Israel using samples taken from a non-cultivated field (control), and plots irrigated with TWW, saline–sodic Jordan River (JR) water, and moderately saline–sodic spring (SP) water. Soil samples were taken at the end of the irrigation season (autumn 2005) and at the end of the subsequent rainy season (spring 2006). In the HC and the aggregate stability determinations, for both sampling seasons, the TWW-irrigated samples gave significantly higher values than the SP- and JR-irrigated samples, but lower than the samples from the control plot. The autumn samples exhibited, generally, higher HC and lower swelling levels compared with the spring samples. Conversely, aggregate stability of the spring samples was higher than that of the autumn samples. These seasonal changes in the results of the three tests were associated with seasonal changes in the salinity and sodicity of the soils. Contributions from the Agricultural Research Organization, The Volcani Center, Bet-Dagan 50250, Israel. No. 601/2007 series.     

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.     

The IWMI water resources paradigm – definitions and implications

Traditional analyses of irrigation performance, especially the concept of irrigation efficiency, can mislead planners and policy makers, especially as water availability at the river basin level becomes the primary constraint to agricultural production. Improving the productivity of water, not land, requires rethinking of some basic `facts' about irrigation performance, new ways of managing, and may be contradictory to some recent trends in institutional reform.     

Influence of boundary plantation of poplar (Populus deltoides M.) on soil–water use and water use efficiency of wheat

Study was undertaken to assess the water use, moisture extraction and water use efficiency (WUE) of irrigated wheat, when grown in association with boundary plantation of poplar, at different distances (0–3, 3–6, 6–9, 9–12, 12–15 and >15 m (control)) from poplar (Populus deltoides M.) tree line. Presence of 3-year old poplar plantation at the boundary of wheat field caused 7.5% higher water use than control (plots having no effect of tree line) up to 3 m distance from tree line which further intensified up to 12.7% and extended up to 6 m distance with 4-year old plantation. Similarly, maximum moisture extraction, both laterally and vertically, observed near the tree line. Contrary to this, WUE of wheat was reduced by 4.6% between 0 and 3 m distance from tree line with 3-year old plantation, decline intensified further to 18.6% with 4-year old plantation. However, wheat was benefited by boundary plantation of trees between 3 and 9 m distance from the base of the tree line which resulted in increased WUE of the wheat crop up to 9%.     

Controlled drainage — effects on drain outflow and water quality

A field experimental project was set up in southern Sweden to assess the effects of controlled drainage on hydrology and environment. Controlled drainage makes it possible to vary the drainage intensity with the variation in drainage requirement during season by controlling the height of a riser in the drain outlet and thus to a certain degree control the amount of outflow of solutes via the drainage system. During periods with low drainage demand, the riser in the drain outlet can be raised and the groundwater level in field will rise up to the level of the riser before the discharge takes place. Three plots, each with an area of 0.2 ha (40 m×50 m) were installed on a loamy sand. One plot was drained by conventional subsurface drainage (CD) and two plots were drained by controlled drainage (CWT). The plots contained four lateral drain tubes, at 10 m spacing and placed at 1 m depth. Each plot was isolated by a double layer of plastic sheeting placed in the back-filled trenches to a depth of 1.6 m to prevent lateral leakage and subsurface interactions. Measurements of precipitation, drain outflow and soil and air temperatures were carried out hourly. Groundwater levels were measured and samples of drain outflow were collected twice a month for nitrogen and phosphorous analyses. Mineral nitrogen contents in soil were measured three times a year.Controlled drainage had a significant hydrological and environmental effect during the 2 years of measurement (1996–1998). Compared with CD, the total drain outflow from CWT was 79% less in Year 1 and 94% in Year 2. The total reduction in nitrate losses with CWT corresponded to the reduced outflow rates. Compared with CD, the total amounts of nitrate in drain outflow were 78% less in Year 1 and 94% in Year 2. The highest concentrations of nitrate were measured at the time of the largest outflow rates. The phosphorous losses were 58% less for CWT as compared to the CD values in Year 1 and 85% less in Year 2. The reduction in nitrogen content in the soil profile during the winter season was 60–70% less in CWT than in CD.     

Response of grapevine cv. ‘Tempranillo’ to timing and amount of irrigation: water relations, vine growth, yield and berry and wine composition

The effects of several moderate irrigation regimes on vine water status, yield, and must and wine composition, were investigated during five seasons in a vineyard planted with Vitis vinifera cv. Tempranillo. Treatments consisted of non-irrigated vines and six differentially irrigated treatments with contrasting watering regimes during the pre-veraison and post-veraison periods. There were large differences in yield and grape and wine quality responses to irrigation among seasons, probably as consequence of the different environmental conditions and crop levels. It was, however, clear that vines benefit more of the irrigation supplied in years of high yield levels. Across seasons, yield increased in proportion to the amount of water applied mostly due to the larger berries of irrigated vines, and there was no clear response to the timing of irrigation supplied. In addition, there were no carry over effects due to irrigation on bud fertility. The post-veraison water application was necessary to increase must sugar level and wine alcohol content. However, water restrictions during the pre-veraison period lead to more concentrated berries in terms of total phenolic and anthocyanins. The only noticeable detrimental effect of irrigation, regardless of the timing of its application, on wine composition was an increase in wine pH.     

Vibration analysis of the fluid-structure  interaction in water hammer

In consideration of the problem that the effect of conduit structure on water hammer has been ignored in the classical theory, the Poisson coupling between the fluid and the pipeline was stu died and a fourteen equation mathematical model of fluid-structure interaction (FSI) was developed in this paper. Then, the transfer matrix method (TMM) was used to calculate the modal frequency, modal shape and frequency response. The results were compared with that in experiment to verify the correctness of the TMM and the results show that the fluid-structure coupling has a greater impact on the modal frequencies than the modal shape. Finally, the influence on the response spectrum of diffe rent damping ratios was studied and the results showed that the natural frequency under different dam ping ratios has changed little but there is a big difference for the pressure spectrum. With the decrease of damping ratio, the damping of the system on frequency spectrum is more and more significant and the dispersion and dissipation is more and more apparent. So the appropriate damping ratio should be selected to minimize the effects of the vibration of the FSI.     

Importance of calcium in irrigation with saline-sodic water — A viewpoint

Saline irrigation waters dominant in sodium salts limit the potential yield of agricultural crops directly by affecting physiological functions of plants and/or indirectly by degrading the soil environment. The vital role of calcium in the regulation of ionic relations in plants and in improving the soil physical condition offers the possibility of combating salinity by both physical manipulation of the soil environment and genetic manipulation of the plant.This paper discusses the physiological role of calcium as related to salt tolerance of crops and also its influence on the structural improvement of salt affected soils. Other aspects covered include the availability of soil calcium to plants and a formula to calculate calcium requirements. Future research needs on the use of calcium in irrigating with saline-sodic water are also indicated.     

Options for alternative irrigation water supplies in the Murray–Darling Basin,Australia: a case study of the Shepparton Irrigation Region

Irrigated agriculture in the Murray–Darling Basin (MDB) currently faces serious challenges due to water scarcity, degradation of water quality, waterlogging and salinity resulting from inappropriate water and land use practices. In particular, there is now increasing risk of water quality degradation due to nutrient rich drainage water in the river system. Therefore, the future of irrigation will depend on the strategies that protect water quality and make best use of water available in the Basin. In this paper, we examine various options that irrigators have to augment water supplies on their farms using the Shepparton Irrigation Region (SIR), Victoria, as a case study. Here, we also discuss the suitability of the ‘Drainage Water Storage Scheme’ (DWSS) in providing additional water supplies to irrigators and in reducing the risk of water quality degradation due to flow of nutrient rich runoff into Basin’s river systems.     

The role of ‘virtual water’ in efforts to achieve food security and other national goals,with an example from Egypt

The term ‘virtual water’ has been used previously to describe the volume of water embodied in food crops that are traded internationally. This paper describes the economic dimension of the ‘virtual water’ concept as an application of comparative advantage, with particular emphasis on water as the key factor of production. The paper also extends the discussion of ‘virtual water’ by describing a nation’s goals regarding food security within a broader framework that includes other objectives such as providing national security, promoting economic growth, and improving the quality of life for citizens. The analysis suggests that land, labor, and capital must also be considered when evaluating a nation’s production and trade opportunities. In countries where one or more of those resources is limiting, focus on ‘virtual water’ alone will not be sufficient to determine optimal policies for maximizing the social net benefits from limited water resources. In countries where labor is relatively abundant, public policies that promote labor-intensive crop production and processing activities may be desirable. The role of ‘virtual water’ within a broader policy framework is demonstrated using crop production and international trade data from Egypt, where substantial amounts of ‘virtual water’ and ‘virtual land’ are embodied in wheat and maize imports. Policies that promote increased exports of labor-intensive crops will improve rural incomes and enhance food security.     

The effect of saline irrigation water on “Shamouti” orange trees

Summary An irrigation experiment with water of different salinities (2.8, 7.6 and 12.7 mol Cl m^–3) was carried out from 1982 to 1988 in a mature Shamouti orange grove in the coastal plain of Israel. Seasonal accumulation of salts in the soil solution of the root zone (EC of more than 4.0 dS m^–1 at the end of the irrigation season) was almost totally leached during the winter. The average annual rainfall of 550 mm reduced EC values below 1.0 dS m^–1. Tree growth, as measured by the increase in cross sectional area of main branches, was retarded by saline irrigation water (123, 107 and 99 cm² growth per tree during six years for the 2.8, 7.6 and 12.7 mol Cl m^–3 treatments, respectively). Potassium fertilization (360 kg K₂O ha^–1) increased yield at all salinity levels during the last three years of the experiment, mainly by increasing fruit size. Saline irrigation water slightly increased sucrose and C1 concentrations in the fruit juice. Salinity decreased transpiration, increased soil water potential before irrigation and decreased leaf water potential. However, the changes in leaf water potential were small. Leaf Cl and Na concentrations increased gradually during the experimental period, but did not reach toxic levels up to the end of the experiment (4.4 g Cl kg^–1 dry matter in the high salt treatment vs. 1.7 in the control). Relatively more leaf shedding occurred in the salinized trees as compared to the control. The sour orange root-stock apparently provided an effective barrier to NaCl uptake; therefore, the main effect of salinity was probably osmotic in nature. No interactions were found between N or K fertilization and salinity. Additional N fertilization (160 kg N ha^–1 over and above the 200 kg in the control) did not reduce Cl absorption nor did it affect yield or fruit quality. Additional K had no effect on Na absorption but yield and fruit size were increased at all salinity levels. No significant differences were obtained between partial and complete soil surface wetting (30% and 90% of the total soil area resp.) with the same amounts of irrigation water. The effect of salinity on yield over the six years of the experiment was relatively small and occurred only after some years. But, in the last three years salinity significantly reduced average yields to 74.6, 67.1, and 64.2 Mg ha^–1 for the three levels of salinity, respectively.These results suggest that saline waters of up to 13 mol Cl m^–3 primarily influence the tree water uptake and growth response of Shamouti orange trees, whereas yield was only slightly reduced during six years.     

More from less – better water management: issues and future policy

The 40 participants of the workshop were divided into four, multi-disciplinary working groups. A deliberate effort was made by the workshop organizers to ensure a range of background disciplines and experience in each group. Each group began with a list of 26 `gaps in knowledge' and 28 `impact opportunities' which they attempted to prioritize and adapt to formulate research themes. The four groups came to surprisingly different conclusions. An attempt is made here to draw some conclusions from the group deliberations that might guide the selection of research topics to be commissioned in the near future under the high potential production system of the Natural Resources Systems Programme (NRSP).     

“WaterMan”: an on-farm water management game with heuristic capabilities

A modern computer-based simulation tool (WaterMan) in the form of a game for on-farm water management was developed for application in training events for farmers, students, and irrigators. The WaterMan game utilizes an interactive framework, thereby allowing the user to develop scenarios and test alternatives in a convenient, risk-free environment. It includes a comprehensive soil water and salt balance calculation algorithm. It also employs heuristic capabilities for modeling all of the important aspects of on-farm water management, and to provide quantitative performance evaluations and practical water management advice to the trainees. Random events (both favorable and unfavorable) and different strategic decisions are included in the game for more realism and to provide an appropriate level of challenge according to player performance. Thus, the ability to anticipate the player skill level, and to reply with random events appropriate to the anticipated level, is provided by the heuristic capabilities used in the software. These heuristic features were developed based on a combination of two artificial intelligence approaches: (1) a pattern recognition approach and (2) reinforcement learning based on a Markov decision processes approach, specifically the Q-learning method. These two approaches were combined in a new way to account for the difference in the effect of actions taken by the player and action taken by the system in the game world. The reward function for the Q-learning method was modified to reflect the suggested classification of the WaterMan game as what is referred to as a partially competitive and partially cooperative game.     

Entrenched views or insufficient science?: Contested causes and solutions of water allocation; insights from the Great Ruaha River Basin,Tanzania

The case study describes large-scale environmental change related to, and recent responses associated with, growing water scarcity in the Usangu Plains, a catchment of the Great Ruaha River in south-west Tanzania. The analysis uses outputs from two recent projects to critically examine various theories of environmental change and the ‘fit’ of new river basin management strategies to the problems found, arguing that various perspectives are worryingly at odds with each other. We find that the investigators of the two projects presented a reasonable and sufficient case of the causes of water scarcity. Yet despite efforts to disseminate scientific findings, different stakeholder groups did not agree with this case. This, we believe, was due to three combined factors; firstly highly entrenched views existed that were also based on quasi-scientific reasoning; secondly, the projects’ deliberations to date, in acknowledging their own uncertainty, were not assertive enough in ascribing causation to the various processes of change; thirdly, policy-uptake was not sufficiently managed by the scientists involved. We conclude that this complexity of the science–policy interface is a feature of integrated water resources management (IWRM) and that the norms of scientific uncertainty in the face of competing theories (held by their protagonists with greater certainty) obliges scientists to take a more active role in sensitively managing the advice-to-policy process in order to improve management of water within river basins. Thus, the paper argues, the nature of integrated water resources management is one of ‘action research’ to move towards an improved understanding of change, and of ‘action policy-advising’ to draw policy-makers into a cycle of considered decision-making.     

Grapevine cv. ‘Riesling’ water use in the northeastern United States

Vine water use was measured in a Vitis vinifera cv. Riesling vineyard located in New York. Vines were fully irrigated and were trained via vertical shoot positioning giving a narrow curtain intercepting about 30% of the incident light during the sunlight hours. Vine water use was estimated on six vines by sap flow gauges directly calibrated with whole canopy transpiration measurements. The regression analysis between estimates of transpiration showed that there were large differences between vines in the calibration values obtained. Sap flow monitoring started late in June, about 2 weeks after bloom, when the canopy already filled the trellis system, and continued until October. Results showed that vine water use during most of the summer days was between 1.0 and 2.0 mm day⁻¹, with peak values around 2.5 mm. The basal (e.g. vine transpiration/reference evapotranspiration) crop coefficient (K _cb) varied somewhat between days, but it was quite stable during the whole season. Averaged over the entire experimental period, the K _cb was 0.49. Some of the day-to-day variation in the K _cb was negatively related with daily average air vapour pressure deficit. This suggests that reference evapotranspiration models on grass may not be fully accurate for vines under these experimental conditions.     

Performance evaluation and control in water delivery decision-making processes: who cares?

This paper focuses on the performance evaluation of different decision-making processes that lead to overall irrigation system performance. First, the key decisions that contribute to the overall system performance in terms of water delivery are identified by means of an analytical framework for irrigation management. Consequently, these key decisions are described briefly and their potential performance indicators listed. The actual use of these performance indicators by two Sri Lankan agencies, government and donor are given in the same lists, which makes it possible to see what these organizations are actually aiming for with respect to water delivery. This approach makes it clear that at the time present the Sri Lankan agencies, government and donor do not care about the water delivery performance. Possibilities for improvement and the role of the different actors are discussed which suggests, at least in Sri Lanka, that initiation of successful performance improvement may have to come from the governments and donors, rather than from the managing agencies themselves.     

Irrigation in the Jordan Valley: Are water pricing policies overly optimistic?

Water is very scarce in the Hashemite Kingdom of Jordan. The development of both public irrigation in the Jordan Valley and private groundwater schemes in the highlands has diverted a large share of the country's water resources to agriculture. Many policy instruments have been used in the last 10 years to reallocate water to nonagricultural uses and encourage improvements in efficiency throughout the water sector. Demand management has been emphasized, with water pricing policies expected to instill conservation and motivate a shift toward higher-value crops. We examine the rationale for, and potential and current impact of, pricing policies in the Jordan Valley.We describe the likelihood of success of such policies in terms of operation and maintenance cost recovery, water savings and improved economic efficiency, and we explore some of the alternatives available for meeting these objectives. We show that while operation and maintenance (O&M) costs can be recovered higher water prices have limited potential for achieving gains in irrigation efficiency. The current system of quotas, the lack of storage, and technical difficulties experienced in the pressurized networks indicate that little water can be saved. More substantial increases in water prices can be expected to raise overall economic efficiency by motivating farmers to intensify cultivation, adopt higher-value crops, improve technology, or rent out their land to investors. Yet such strategies are constrained by lack of capital and credit, and pervasive risk, notably regarding marketing. Pricing policies, thus, are best implemented together with positive incentives that reduce capital and risk constraints, and offer attractive cropping alternatives or exit options with compensation.     

Plant water requirement of ‘Hamlin’ sweet orange in cold temperature conditions

Citrus irrigation scheduling is usually based on evapotranspiration (ET) multiplied by a crop coefficient that varies throughout the year. However, ET at 10°C and less has not been investigated. Citrus acclimate to temperatures below 10°C, which affects ET, and therefore may allow irrigation scheduling to be adjusted accordingly. Three separate growth chamber experiments were conducted in complete block design with two temperature treatments and 8-one tree replications with the objective of determining water use of ‘Hamlin’ orange exposed to cold temperatures. The treatments included: full cold-acclimating temperatures, alternating 10 days cold and 3 days warm temperatures, and alternating 10 days warm and 3 days cold temperatures. Although well-watered, trees exposed to temperatures ≤10°C demonstrated lower water use compared to trees held at temperatures that promoted growth. Reduction of water use of cold-treated plants than the controls was 66, 20–57, and 14–28% during full cold-acclimating temperatures, alternating 10 days cold and 3 days warm, and alternating 10 days warm and 3 days cold temperatures, respectively. Reduced water use of cold-treated plants was due to stomatal closure, increased root resistance, and decreased leaf area. Effective irrigation scheduling based on water requirements as they change during cold-acclimating temperatures should save water while providing adequate water for yield and quality.