Modeling shallow water table evaporation in irrigated regions

Groundwater discharge through evaporation due to a shallow water table can be an important component of a regional scale water balance. Modeling this phenomenon in irrigated regions where soil moisture varies on short time scales is most accurately accomplished using variably saturated modeling codes. However, the computational demands of these models limit their application to field scale problems. The MODFLOW groundwater modeling code is applicable to regional scale problems and it has an evapotranspiration package that can be used to estimate this form of discharge, however, the use of time-invariant parameters in this module result in evaporation rates that are a function of water table depth only. This paper presents a calibration and validation of the previously developed MOD-HMS model code using lysimeter data. The model is then used to illustrate the dependence of bare soil evaporation rates on water table depth and soil moisture conditions. Finally, an approach for estimating the time varying parameters for the MODFLOW evapotranspiration package using a 1-D variably saturated MOD-HMS model is presented.     

Assessment of alternative water management options for irrigated agriculture

A simulation study on alternative water management strategies was carried out for Sirsa Irrigation Circle in Haryana, covering an area of about 4800 km². Results showed that crop evapotranspiration and soil salinity development under reduction in canal water supply and increase in groundwater use, are largely influenced by the amount and distribution of rainfall. Reduction in canal water supply by 25% during the rainy season is unlikely to have any adverse effect on the salinity development in the study area. Reduction in crop evapotranspiration due to decreased canal water supply can partly be compensated by the increase in groundwater use. Leaching of salts due to monsoon rains in the study area shows that groundwater of even relatively poor quality can be used for irrigation without excessive long-term build up of soil salinity under deep groundwater depth conditions. However, increased groundwater extraction without associated actions will not be very effective to solve the problem of rising groundwater levels.     

A simple dated water-production function for use in irrigated agriculture

Dated water-production functions are useful in evaluating alternative irrigation strategies. The dated water-production functions commonly used in irrigation-optimization models are briefly reviewed. Based on the heuristic assumption that the Boolean principle is applicable, a simple multiplicative dated water-production function is proposed. The function was compared for a number of crops, with the Stewart-Hagan-Pruitt and Jensen models. The proposed model is shown to be applicable over a wide range of stress conditions.     

The impact of agriculture on ground water quality in Slovenia: standards and strategy

Ground water and water from springs are sources used for water supply in Slovenia. The quality of these waters has been monitored since 1987. Among 12 main ground water aquifers in Slovenia the amount of nitrate exceeds the allowable level (50 mg/l) for drinking water in areas with more intensive agricultural production with higher concentrations of animals (two livestock unit – LU/ha) and where drainage of sewage water is not excellently arranged or where quality of river water that effluent ground water is not well. The identification of nitrogen surpluses has been done on regional and farm level (using normative approach). This method is taking into account nitrogen input from mineral fertiliser, animal wastes and the deposition from the atmosphere minus nitrogen uptake of harvested crops and ammonia losses to the atmosphere. On an average nitrogen input from mineral fertiliser is low, while input from organic manure is rather high – 90 kg/ha. Average net-balance surplus for Slovenia is about 56 kg N/ha. The differences between regions are relatively high. In the most intensive arable region with high intensity of animal husbandry (2 LU/ha) nitrogen surplus is about 90 kg/ha. This region can be identified as vulnerable for nitrogen leaching into ground water. In regions with limited growing conditions for agriculture plants (climate, soil depth) just small increase of livestock density can cause high nitrogen surpluses. Our Slovenian legislation, which almost entirely corresponds to EC Nitrate Directive and Code of Good Agricultural Practice intends to reduce mineral surpluses in agriculture and meet the standards of nitrate in drinking water.     

Simulating root water uptake from a shallow saline groundwater resource

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal to deal with this problem is sequential biological concentration (SBC), which is the process of recycling drainage water on increasingly more salt tolerant crops until the volume of drainage water has been reduced sufficiently to enable its final disposal by evaporation in a small area. For maximum effectiveness this concept will require crop water reuse from shallow groundwater. To evaluate the concept of sequential biological concentration, a column lysimeter study was used to determine the potential crop water use from shallow groundwater by alfalfa as a function of ground water quality and depth to ground water. However, lysimeter studies are not practical for characterizing all the possible scenarios for crop water use related to ground water quality and depth. Models are suited to do this type of characterization if they can be validated. To this end, we used the HYDRUS-1D water flow and solute transport simulation model to simulate our experimental results. Considering the precision of the experimental boundary and initial conditions, numerical simulations matched the experimental results very well. The modeling results indicate that it is possible to reduce the dependence on experimental research by extrapolating experimental results obtained in this study to other specific sites where shallow saline groundwater is of concern.     

Impact of different water price levels on irrigated agriculture in Northern Jordan Valley

A linear programming model was developed to assess the impact of different water prices on cultivated areas, irrigation water demand, net income and optimal cropping pattern in the Northern Jordan Valley (NJV). The results reveal that the price for irrigation water does not reflect any elasticity in the range of water prices between 0.01 and 0.06 JD/M³ indicating constant real economic water price of 0.06 JD/M³. The change in cultivated areas as well as water demand (reduction) starts at water price 0.07 JD/M³. The expected reductions under optimal cropping patterns are 5%, 24%, and 60% for cultivated area and 4.7%, 18.9%, and 31% for water demand with water prices at 0.07, 0.1, and 0.16 JD/M³, respectively. Significant reductions in net incomes are resulted with increasing water prices over current average water price of 0.025 JD/M³. The expected reductions in net incomes are 33.6%, 53.8%, and 81.4% at water prices 0.07, 0.1, and 0.16 JD/M³, respectively. This result reflects the low land profitability as a result of low land productivity and/or low farm gate sale prices for most crops grown in NJV. The study also shows the inconsistency in quantity of water supplied and water demanded, leading to unbalanced water budget on monthly level and inconsequence, a noticeable waste in the quantity of available water during winter months, although there is a net surplus of water over the year. While the findings of this research reveal that a water price in the range of 0.07?C0.1 JD/M³ does not significantly influence the farmers' socio-economic parameters in the NJV, it may help reach the stated goal of saving water especially when monthly distributions of irrigation water are based on real crops water demands and actual cropping patterns.     

Sugarcane water use from shallow water tables: implications for improving irrigation water use efficiency

The resource potential of shallow water tables for cropping systems has been investigated using the Australian sugar industry as a case study. Literature concerning shallow water table contributions to sugarcane crops has been summarised, and an assessment of required irrigation for water tables to depths of 2 m investigated using the SWIMv2.1 soil water balance model for three different soils. The study was undertaken because water availability is a major limitation for sugarcane and other crop production systems in Australia and knowledge on how best to incorporate upflow from water tables in irrigation scheduling is limited. Our results showed that for the three soils studied (representing a range of permeabilities as defined by near-saturated hydraulic conductivities), no irrigation would be required for static water tables within 1 m of the soil surface. Irrigation requirements when static water tables exceeded 1 m depth were dependent on the soil type and rooting characteristics (root depth and density). Our results also show that the near-saturated hydraulic conductivities are a better indicator of the ability of water tables below 1 m to supply sufficient upflow as opposed to soil textural classifications. We conclude that there is potential for reductions in irrigation and hence improvements in irrigation water use efficiency in areas where shallow water tables are a low salinity risk: either fresh, or the local hydrology results in net recharge.     

Consumptive water use and crop coefficients of irrigated sunflower

In semi-arid environments, the use of irrigation is necessary for sunflower production to reach its maximum potential. The aim of this study was to quantify the consumptive water use and crop coefficients of irrigated sunflower (Helianthus annuus L.) without soil water limitations during two growing seasons. The experimental work was conducted in the lysimeter facilities located in Albacete (Central Spain). A weighing lysimeter with an overall resolution of 250 g was used to measure the daily sunflower evapotranspiration throughout the growing season under sprinkler irrigation. The lysimeter container was 2.3 m × 2.7 m × 1.7 m deep, with an approximate total weight of 14.5 Mg. Daily ET _c values were calculated as the difference between lysimeter mass losses and lysimeter mass gains divided by the lysimeter area. In the lysimeter, sprinkler irrigation was applied to replace cumulative ET _c, thus maintaining non-limiting soil water conditions. Seasonal lysimeter ET _c was 619 mm in 2009 and 576 mm in 2011. The higher ET _c value in 2009 was due to earlier planting and a longer growing season with the maximum cover coinciding with the maximum ET _o period. For the two study years, maximum average K _c values reached values of approximately 1.10 and 1.20, respectively, during mid-season stage and coincided with maximum ground cover values of 75 and 88 %, respectively. The dual crop coefficient approach was used to separate crop transpiration (K _cb) from soil evaporation (K _e). As the crop canopy expanded, K _cb values increased while the K _e values decreased. The seasonal evaporation component was estimated to be about 25 % of ET _c. Linear relationships were found between the lysimeter K _cb and the canopy ground cover (f _c) for the each season, and a single relationship that related K _cb to growing degree-days was established allowing extrapolation of our results to other environments.     

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.     

Building a climate resilient farm: A risk based approach for understanding water, energy and emissions in irrigated agriculture

The links between water application, energy consumption and emissions are complex in irrigated agriculture. There is a need to ensure that water and energy use is closely considered in future industry planning and development to provide practical options for adaptation and to build resilience at the farm level. There is currently limited data available regarding the uncertainty and sensitivity associated with water application and energy consumption in irrigated crop production in Australia. This paper examines water application and energy consumption relationships for different irrigation systems, and the ways in which the uncertainty of different parameters impacts on these relationships and associated emissions for actual farms. This analysis was undertaken by examining the current water and energy patterns of crop production at actual farms in two irrigated areas of Australia (one using surface water and the other groundwater), and then modelling the risk/uncertainty and sensitivity associated with the link between water and energy consumption at the farm scale. Results showed that conversions from gravity to pressurised irrigation methods reduced water application, but there was a simultaneous increase in energy consumption in surface irrigation areas. In groundwater irrigated areas, the opposite is true; the use of pressurised irrigation methods can reduce water application and energy consumption by enhancing water use efficiency. Risk and uncertainty analysis quantified the range of water and energy use that might be expected for a given irrigation method for each farm. Sensitivity analysis revealed the contribution of climatic (evapotranspiration and rainfall) and technical factors (irrigation system efficiency, pump efficiency, suction and discharge head) impacting the uncertainty and the model output and water-energy system performance in general. Flood irrigation systems were generally associated with greater uncertainty than pressurised systems. To enhance resilience at the farm level, the optimum situation envisaged an irrigation system that minimises water and energy consumption and greenhouse gas emissions. Where surface water is used, well designed and managed flood irrigation systems will minimise the operating energy and carbon equivalent emissions. Where groundwater is the dominant use, the optimum system is a well designed and managed pressurised system operating at the lowest discharge pressure possible that will still allow for efficient irrigation. The findings might be useful for farm level risk mitigation strategies in surface and groundwater systems, and for aiding adaptation to climate change.     

Growth and water use of eucalypt trees irrigated with saline drainage water

Leaf chemical composition, growth and water use of Eucalyptus camaldulensis (Lake Albacutya provenance) were measured in the 4th year of a split-plot salinity by nutrition trial. The main plot consisted of irrigating with five different water salinities: 0.5 dS/m (S0.5), 2 dS/m (S2), 5 dS/m (S5), 7.5 dS/m (S7.5) and 10 dS/m (S10). The subplot treatments consisted either of annual additions of 200 kg N and 100 kg P per hectare (+ N + P) or no addition of nutrients (– N – P). Irrigation with water from a drainage system (treatments S2, S5, S7.5 and S10) added about a further 100 kg N/ha annually. Leaf concentrations of N and P were higher in the + N + P treatments. In S0.5, nutrient addition stimulated growth. In + N + P treatments, raising the irrigation salinity from 0.5 to 2.0 dS/m increased leaf Na and decreased the growth rate, however, further increases in salinity affected neither leaf Na nor growth. In – N – P, growth rate depression due to inadequate nutrition was overcome in S2 and S5 by the 100 kg/ha of N in the drainage water. At higher salinities, the N added by drainage water did not overcome the effect of inadequate nutrition. On days when the reference crop evapotranspiration (ETo) was less than 3 mm/day, the correlations between water use of trees in litres per day and ETo and between water use of trees in litres per day and the basal area of the tree butt were highly significant. On days when the ETo was 3 mm/day or greater, the correlation between tree water use and basal area was highly significant, but that between tree water use and ETo was not significant. Received: 15 March 1996     

Root growth, water potential and yield of irrigated wheat

Root length density (LV), mid-day leaf water potential (Ψ _leaf) and yield of wheat were studied in 1983 – 1984 and 1984 – 1985 on a Phoolbagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.4 – 0.9 m, SWT) and medium-depth (0.8 – 1.3 m, MWT) water table conditions with six water regimes: rainfed (I₀); irrigation at cown root initiation (I₁); at crown root initiation and milk (I₂); at crown root initiation, maximum tillering and milk (I₃); at crown root initiation, maximum tillering, flowering and milk (I₄); and at crown root initiation, maximum tillering, flowering, milk and dough (I₅). Maximum rooting depth (0.8 m under SWT and 1.05 m under MWT conditions) was attained at the dough stage (115 days after sowing, DAS) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (I₂– I₅), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimens (I₀ and I₁), due to deficient moisture conditions in the upper soil layer (0.45 m) they invaded lower horizons and had a greater vertical distribution Ψ _leaf was not significantly affected by water regime (I₁– I₅) up to 94 DAS during a wet year (1983 – 1984) and up to 74 DAS during a dry year (1984 – 1985), but was significantly affected thereafter. Grain yields with water regimens I₁– I₅ during a wet year and for the I₂– I₅ treatments during a dry year at either water table depth were not significantly different, but there was a (non-significant) trend to lower yield with increasing soil water deficit. Under SWT in I₂, the average grain yield wsa 5130 kg ha^–1 and under the I₃ regime, 5200 kg ha^–1. Likewise, under MWT in I₃, it was 5188 kg ha^–1 and under the I₄ regime, 5218 kg ha^–1. The results indicate that application of irrigation of more than 120 and 180 mm under SWT and MWT conditions, respectively, did not raise yield. Irrigation given as per schedule I₂ under SWT and I₃ under MWT conditions in the Tarai situation, appears to be more effective than a very wet regime (I₅). Received: 9 December 1997     

Urban growth, wastewater production and use in irrigated agriculture: a comparative study of Accra, Addis Ababa and Hyderabad

The relationships between urban development, water resources management and wastewater use for irrigation have been studied in the cities of Accra in Ghana, Addis Ababa in Ethiopia and Hyderabad in India. Large volumes of water are extracted from water sources often increasingly far away from the city, while investments in wastewater management are often lagging behind. The resulting environmental degradation within and downstream of cities has multiple consequences for public health, in particular through the use of untreated wastewater in irrigated agriculture. Despite significant efforts to increase wastewater treatment, options for safeguarding public health via conventional wastewater treatment alone remain limited to smaller inner-urban watersheds. The new WHO guidelines for wastewater irrigation recognize this situation and emphasize the potential of post- or non-treatment options. Controlling potential health risks will allow urban water managers in all three cities to build on the benefits from the already existing (but largely informal) wastewater reuse, those being the contribution to food security and reduction of fresh water demands.     

Rising water table: A threat to sustainable agriculture in an irrigated semi-arid region of Haryana, India

The sustainability of the rice-wheat cropping system in an irrigated semi-arid area of Haryana State (India) is under threat due to the continuous rise in the poor quality groundwater table, which is caused by the geo-hydrological condition and poor irrigation water management. About 500,000 ha in the State are waterlogged and unproductive and the size of the waterlogged area is increasing. We analyse the hydrology and estimate seasonal net groundwater recharge in the study area. Rainfall is quite variable, particularly in the monsoon season, and the mean monthly reference evapotranspiration shows a high inter-annual variation, with values between 2.45 and 8.47 mm/day in December and May. Groundwater recharge analysis during the study period (1989-2008) reveals that percolation from irrigated fields is the main recharge component with 57% contribution to the total recharge. An annual groundwater table rise of 0.137 m has been estimated for the study area. As the water table has been rising continuously, suitable water management strategies such as increasing groundwater abstraction by installing more tubewells, using the groundwater conjunctively with good quality canal water, changes in cropping patterns, adoption of salt tolerant crops, changes in water-pricing policy, and matching water supply more closely with demand, are suggested to bring the water table down to a safe limit and to prevent further rising of the water table.     

农业高效用水及农艺节水技术

节水农业的中心问题是提高降水和灌水的利用效率,用水有效性无疑成为判断各种节水措施效果与潜力的标准。但用水有效性是一个相对概念,节水农业的标准也是比较型的,是与纵向和横向比较而言的,是可变的。随着科技的不断进步,节水措施的标准应该由有效用水向高效用水发展。高效用水农业就是高标准节水农业。就一个国家或一个地区而言,可以根据国情和地域情况制定一个节水农业的标准,如井灌区水的利用率为０７０,水的利用效率为１．２ｋｇ／ｍ３以上,可称为节水农业;水的利用率为０８５以上,水的利用效率达１．８ｋｇ／ｍ３以上…     

Assessing ground water quality in the irrigated plain of Triffa (north-east Morocco)

Irrigated agriculture in (semi-)arid regions may exert serious pressures on groundwater resources and jeopardise further agricultural and socio-economical developments. For assessing these pressures, we present in this paper results from a groundwater quality survey performed in 2005 within the irrigated agricultural Triffa plain in north-east Morocco. The study focuses on the physico-chemical and bacteriological quality of the groundwater body within the plain and exploits the correlation and spatial dependency of the quality parameters. It is demonstrated that the water quality in this region is critical. Nitrate levels are situated between 2 and 153 mg/l, with 73% of the observations exceeding the critical level of 50 mg/l. Nitrite, ammonia, orthophosphate and dissolved organic matter content do not exceed existing norms. Bacteriological residues (faecal, total coliforms, faecal streptococcus and clostridium sulfido-reductants), however, are retrieved in nearly all water samples. Bacteriological contamination is merely correlated with nitrite and ammonia content rather than with nitrate content, indicating a possible contribution of local pollution sources to groundwater deterioration. The variability of the nitrate and bacteriological pollution is important and spatially correlated. The spatially dependency is modelled using spherical and Gaussian semi-variograms and is used to map the nitrate and bacteriological contamination using ordinary kriging techniques. The results shown are significantly different as compared to earlier studies on groundwater quality for the studied aquifer. The differences may be explained partially by modified but inappropriate fertilizer management practices in combination with intensive irrigation. Given the agricultural developments in this area, further deterioration of the groundwater quality is expected if no mitigation strategies are developed.     

Increasing productivity in irrigated agriculture: Agronomic constraints and hydrological realities

Irrigation is widely criticised as a profligate and wasteful user of water, especially in watershort areas. Improvements to irrigation management are proposed as a way of increasing agricultural production and reducing the demand for water. The terminology for this debate is often flawed, failing to clarify the actual disposition of water used in irrigation into evaporation, transpiration, and return flows that may, depending on local conditions, be recoverable. Once the various flows are properly identified, the existing literature suggests that the scope for saving consumptive use of water through advanced irrigation technologies is often limited. Further, the interactions between evaporation and transpiration, and transpiration and crop yield are, once reasonable levels of agricultural practices are in place, largely linear—so that increases in yield are directly and linearly correlated with increases in the consumption of water. Opportunities to improve the performance of irrigation systems undoubtedly exist, but are increasingly difficult to achieve, and rarely of the magnitude suggested in popular debate.     

Root growth, water potential, and yield of irrigated rice

Root length density (Lv), leaf water potential (Ψ leaf) and yield of rice were studied in 1983 and 1984 on a Phool bagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.07–0.92 m) and medium-depth (0.13–1.26 m) water table conditions with six water regimes ranging from continuous submergence under 0.05 m ± 0.02 m (Ic) to completely rainfed (Io). In irrigation treatments, Ic1, Ic3, Ic5, and Ic7, 0.07 m irrigation was applied on days 1, 3, 5, and 7 respectively, after the disappearance of ponded water. Maximum rooting depth (0.55 m in the shallow and 0.65 m in the medium-depth water table) was attained at the dough stage (125 days after transplanting) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (Ic1–Ic5), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimes, (Ic7 and Io) they were concentrated in lower horizons and had a more vertical distribution. Like Lv, Ψ leaf was not significantly affected by water regime up to 90–95 days after rice transplanting but was significantly affected thereafter, except for Lv beneath 0.2 m–0.25 m. Grain yields with irrigation treatments Ic1 and Ic3 under shallow and Ic1 under medium-depth water table conditions were not significantly different from those under continuous submergence, but there was a (nonsignificant) trend to lower yield with less water. However, differences among the wet regimes (Ic, Ic1, and Ic3) were small (141–490 kg ha^–1) under shallow and 413–727 kg ha^–1 under medium-depth water table conditions. The results demonstrate that optimum yield (5500–6000 kg ha^–1) could be obtained under Tarai conditions by adopting an intermittent irrigation schedule of 3–5 days after the disappearance of ponded water under shallow, and of 1–3 days under medium-depth water table conditions, in place of continuous submergence. Received: 26 February 1996