Brackish Water Irrigation Research Articles

Soil matric potential and salt transport in response to different irrigated lands and soil heterogeneity in the North China Plain

In the lowland area of the North China Plain (NCP), increasing utilization of brackish water could promote the transformation of precipitation into available water resources, and alleviate the conflict between increase food production and freshwater scarcity. However, the processes of soil water movement and salt migration might be altered, because utilization of brackish water results in frequent changes in groundwater depth and thickness of vadose zone. Thus, it was necessary to understand soil water movement and salt migration when using brackish water for irrigation. In this study, soil matric potential (SMP) and total dissolved solids (TDS) at multiple depths were measured in situ to investigate the mechanisms of soil water movement and salt migration at one grassland (site 1) and at three typical irrigated croplands (sites 2, 3, and 4) with different soil textures and groundwater depths in a lowland area of the NCP. The study showed that deep soil water and groundwater were recharged generally following heavy precipitation during rainy season. SMP values increased quickly at site 4 due to relatively homogeneous soils, followed by site 3 > site 2 > site 1 with an obvious hysteresis response of SMP at multiple depths to precipitation. Soil water mainly moved downward in piston flow, and preferential flow also existed in the soil above 100 cm in the percolation process at four sites. Generally, SMP values followed the order of site 4 > site 1 > site 2 > site 3 and exhibited an inverse trend for TDS, which was mainly due to soil heterogeneity and soil texture in vertical profiles. The differences in SMP among the four sites were mainly due to land use and groundwater depth. There were significantly differences in spatiotemporal distribution of water and salts between homogenous and heterogeneous soils. The processes of infiltration and water redistribution ended quickly in relatively homogeneous soils after heavy rains. However, there was obvious hysteresis in SMP with an increase in soil depth in heterogeneous soils. Homogenous soils favored water infiltration, salt leaching, and groundwater recharge, and the flow of soil water flow was blocked and salt accumulated significantly in layered soils. The soil water movement and the transformation relationship between water and salt in the vadose zone provided a basis for utilization of brackish water irrigation in lowland region of the NCP.

Isolation and Molecular Identification of Naegleria australiensis in Irrigation Water of Fuerteventura Island, Spain.

Saline groundwater desalination has recently emerged as an alternative source of irrigation water in arid and semiarid regions due to the gradual reduction in the quantity and quality of conventional water resources for agricultural use. In Fuerteventura Island (Spain), an extremely arid territory in the European Union, brackish water desalination is one of the few available water sources for agricultural production. Very little research has been conducted on the microbiological quality of this water mainly used for irrigation of vegetable crops. Free-living amoebae (FLA) are widely distributed protozoa in the environment and have been isolated from many environmental sources such as dust, soil and water. Among the pathogenic genera included in this group, Acanthamoeba spp., Naegleria fowleri and Balamuthia mandrillaris have been reported to be causative agents of lethal encephalitis, disseminated infections and keratitis. Particularly, Naegleria fowleri is a pathogenic FLA species which causes primary amoebic meningoencephalitis (PAM). In the present study, the presence of pathogenic FLA strains on desalinated brackish water samples for irrigation has been evaluated during 7months. From the analysed samples, only one was positive for Naegleria australiensis. This is the first report of Naegleria spp. in desalinated brackish water for irrigation in Spain.

Effects of foliar application of glycine betaine and chitosan on Puccinellia distans (Jacq.) Pari, subjected to salt stress.

Using brackish water for irrigation may expose turfgrasses to salinity stress. Employing the best treatments to maintain high-quality turfs under saline conditions is an important requirement for turfgrass management. We tested the response of a halophyte grass, Puccinellia distans, to irrigation with saline solutions and to foliar application of two osmoprotectants, such as glycine betaine (GB) or chitosan (CH). Plants were grown in pots under controlled conditions and irrigated with 200 mM or 600 mM of NaCl solutions. The response to salinity treatments and osmoprotectant application was evaluated after 90 days by measuring leaf firing, leaf density, shoot length and biomass, root length, and shoot water potential. Increasing salinity reduced shoot density, shoot and root length, shoot water potential, and increased leaf firing and shoot solute potential at 200 mM of NaCl. These effects were more pronounced at 600 mM of NaCl. Application of GB greatly increased shoot growth traits at 200 mM of NaCl and also showed beneficial effects on most traits at 600 mM. Application of CH showed positive effects only on leaf firing and leaf water potential at 600 mM. Our results show that P. distans can tolerate high levels of salt stress, which can be best alleviated by GB treatment.

Modelling the Impact on Root Water Uptake and Solute Return Flow of Different Drip Irrigation Regimes with Brackish Water

Water scarcity and quality degradation represent real threats to economic, social, and environmental development of arid and semi-arid regions. Drip irrigation associated to Deficit Irrigation (DI) has been investigated as a water saving technique. Yet its environmental impacts on soil and groundwater need to be gone into in depth especially when using brackish irrigation water. Soil water content and salinity were monitored in a fully drip irrigated potato plot with brackish water (4.45 dSm−1) in semi-arid Tunisia. The HYDRUS-1D model was used to investigate the effects of different irrigation regimes (deficit irrigation (T1R, 70% ETc), full irrigation (T2R, 100% ETc), and farmer’s schedule (T3R, 237% ETc) on root water uptake, root zone salinity, and solute return flows to groundwater. The simulated values of soil water content (θ) and electrical conductivity of soil solution (ECsw) were in good agreement with the observation values, as indicated by mean RMSE values (≤0.008 m3·m−3, and ≤0.28 dSm−1 for soil water content and ECsw respectively). The results of the different simulation treatments showed that relative yield accounted for 54%, 70%, and 85.5% of the potential maximal value when both water and solute stress were considered for deficit, full. and farmer’s irrigation, respectively. Root zone salinity was the lowest and root water uptake was the same with and without solute stress for the treatment corresponding to the farmer’s irrigation schedule (273% ETc). Solute return flows reaching the groundwater were the highest for T3R after two subsequent rainfall seasons. Beyond the water efficiency of DI with brackish water, long term studies need to focus on its impact on soil and groundwater salinization risks under changing climate conditions.

Soil Microbial Metabolic Activity and Community Structure in Drip-Irrigated Calcareous Soil as Affected by Irrigation Water Salinity

Saline water irrigation can dramatically change the soil environment and thereby influence soil microbial processes. The objective of this field experiment was to use Biolog and high-throughput sequencing methods to evaluate the metabolic activity and community structure of soil microorganisms after 9 years of saline water irrigation. The results showed that brackish and saline water irrigation significantly increased soil bulk density and salinity, but significantly decreased soil pH, TN, SOM, MBC, and metabolic activity. The Biolog tests of sole-carbon-source utilization indicated that the brackish and saline water treatments significantly reduced the utilization of four carbohydrate sources (D-cellobiose, β-methyl-d-glucoside, D-mannitol, and glucose-1-phosphate), two amino acid sources (L-asparagine and glycyl-L-glutamic acid), two carboxylic acid sources (D-galacturonic acid and D-malic acid), and two polymer sources (Tween 80 and glycogen). Brackish and saline water increased soil bacterial richness (ACE and Chao 1 indices) but had no effect on which bacterial phyla were present. Brackish and saline irrigation water significantly increased the relative abundance of four dominant bacterial phyla (Gemmatimonadetes, Actinobacteria and Chloroflexi, Saccharibacteria). In contrast, the relative abundance of five dominant phyla (Proteobacteria, Acidobacteria, Nitrospirae, Planctomycetes, and Verrucomicrobia) was reduced by brackish and saline irrigation water. Our study suggests that soil bacterial community will form significant differences species under different irrigation water salinity, which can adapt to saline stress by adjusting the species composition. The results of this study increase understanding about the potential effects of saline water irrigation on soil biological processes.

Effects of brackish water irrigation on Photosynthesis and yield of Winter Wheat

In this paper, winter wheat was used as the research object. The chlorophyll content, net photosynthetic rate, light response curve and yield of winter wheat were compared with the experimental data from 2015 to 2017.The results show that:The brackish water of 3g/L has little effect on chlorophyll content. The physiological growth of winter wheat could be promoted by irrigation with 3 g/L brackish water at jointing stage, and photosynthesis could be promoted by appropriate salt stress. Salt stress can change the way crops use effective light radiation. The brackish water of 3g/L can promote the utilization efficiency of low effective light radiation in winter wheat. The brackish water of 5g/l will affect the leaf structure of winter wheat, reduce the response of leaves to high effective light radiation, and eventually lead to the decline of photosynthesis. Two years of brackish water irrigation will have a certain effect on crop yield.

Effect on Soil Properties and Maize Growth by Alternate Irrigation with Brackish Water

Abstract. With growing competition for freshwater by industrialization and urbanization, brackish water irrigation has been increasingly used for agricultural production. One of major concerns is the accumulation of salt and its impacts on soil properties and crop yield. If properly managed, alternate irrigation with brackish and freshwater might alleviate the adverse impacts of salt on soil physicochemical properties and plant growth. To exploit proper alternate irrigation to minimize such impacts, a maize pot experiment was conducted at three stages (seedling, jointing and tasseling, and after tasseling) with three alternate irrigation methods (BFF: brackish-fresh-fresh, FBF: fresh-brackish-fresh, and FFB: fresh-fresh-brackish) and with three salinities (1.69, 4.81, and 7.94 dS m-1), respectively. The results show that compared to freshwater irrigation, alternate irrigation with high-salinity brackish water increased soil electrical conductivity by 4.1% to 207.4% and reduced soil infiltration rate by 19.2% to 51.9%. The adverse impacts were more prominent in FBF and FFB than in BFF due to the higher proportions of brackish water in FBF and FFB. High-salinity brackish water also caused salt stress on maize growth and decreased evapotranspiration, relative water content, intrinsic water use efficiency, and electron transport rate by 6.6% to 30.6%, 2.1% to 10.2%, 7.3% to 17.9%, and 7.2% to 39.6%, respectively, leading to reduced growth and productivity. The salt stress was more pronounced in BFF and FBF than in FFB because maize is more salt-sensitive during the vegetative stage. Overall, brackish water irrigation at the jointing and tasseling stage (FBF) caused the most severe impacts on both soil and maize, so freshwater is advocated at this stage. In BFF, due to sufficient freshwater irrigation at later stages, slightly saline irrigation can be applied at the seedling stage without evident adverse effects. Higher-salinity brackish water was used successfully in the after-tasseling stage (FFB), although salt leaching by off-season rainfall was needed after harvest for sustainable production. Keywords: Crop yield, Saline water, Salt stress, Soil salinity, Water use efficiency.

GMO or OMG?

Just when it looked like there could be a breakthrough in the application of biotechnology to crops and food plants, a new wrinkle appeared in the form of a scientific development. Genetically modified organisms (GMOs) have been planted for years because they offer advantages for producers or consumers. For instance, there are GMO corn, soybean, and cotton crops that are immune to the effects of common herbicides that are used to control weeds; this makes them easier and more economical to grow. There are new apple varieties genetically modified to produce enzymes so that they do not turn brown when cut open; these are supposed to appeal to consumers who like to have their fruit look as good when cut open even days before as if it was freshly cut. There are vegetables genetically modified to contain higher levels of certain vitamins and other nutrients; these can help alleviate malnourishment in underdeveloped countries. There are genetic changes to crops and food plants that can tolerate climate and environmental changes such as warmer temperatures or brackish irrigation water and still thrive; these may be necessary in order to feed the many billions more people expected to live on Earth in the coming years.

Environmental Scanning Electron Microscopy Application for Brackish Water Irrigation Impact on Soil

Core Ideas Long‐term irrigation with brackish water can extend the practice into water‐scarce regions. ESEM in both dynamic and static modes is a promising technique to analyze soil impacts. Changes linked to the hydrophilic behavior of soils can be detected. We investigated soil response to irrigation with slightly brackish water (1200 mg L−1 total dissolved solids on average) in a semiarid environment at the microscopic scale using environmental scanning electron microscopy (ESEM) applied in static and dynamic modes, which allowed comparison between nonirrigated and 3‐yr‐irrigated soil samples to determine the impact of applied brackish water. Results indicate that (i) there was a change in soil hydrophilic behavior by the continuous accumulation of water‐borne salt in the soil matrix, (ii) compared with nonirrigated samples, the wetting process occurred more gradually for the 3‐yr‐irrigated sample, (iii) the wetting process started at a lower vapor pressure for the 3‐yr‐irrigated sample, (iv) water vapor pressure in the chamber at full saturation was lower for the 3‐yr‐irrigated sample, and (v) the presence of heavy metals in the soil was more frequent in irrigated samples. Our results show that ESEM is a useful technique to determine the impacts on soil of irrigation with slightly brackish water.

Effect of Brackish Water Irrigation on soil Water-salt Distribution

The experiment of winter wheat brackish water irrigation was carried out in Xiawa Town, Zhanhua District, Shandong Province from 2015 to 2016. Four different irrigation schemes were designed by using fresh water and brackish water of salinity of 3.0g/L. The effect of brackish water irrigation on the distribution of water-salt in saline alkali soil was studied. The results showed that the soil water content of three times irrigation could reach 12.5% ∼ 19.9%, while that of twice irrigation could only reach 10.8% ∼ 13.6% and the salt accumulation of the scheme of fresh water + fresh water + brackish water was 0.0552g/kg, which indicated that this scheme could not only supplement soil water but also accumulate less salt.

Brackish water irrigation on the characteristics of carbon, nitrogen and phosphorus nutrients in the soil nearby crop roots

To study the effect of brackish water on carbon, nitrogen and phosphorus in the soil nearby root zone of crops. By analyzing the influence of different levels of salt and fresh water combination irrigation on organic carbon, nitrogen and phosphorus migration rule in the soil, and the dynamic change rule in different sections to investigate the spatial distribution of each index at the end of the experiment. According to the soil properties and root distribution of Zizyphusjujuba, brackish water drip irrigation quota, irrigation water salinity and fertilization measures of root zone, different gradient levels of combined irrigation experiments were set up. The experiment with fresh water was used as control to establish orthogonal test scheme. The content of carbon, nitrogen and phosphorus in soil nearby crop roots was measured, and the measurement of carbon, nitrogen and phosphorus in the soil nearby crop roots was utilized to analyze the effect of brackish water irrigation on the soil nearby crop roots. With the increase of brackish water amount for irrigation, nitrate and alkali nitrogen content in the soil nearby roots was significantly decreased, and the reduction trend is going up after a significant amount of brackish water for irrigation is added. While phosphorus content decreased at different levels after brackish water amount for irrigation was increased, but the decrease is not significant. Brackish water irrigation with appropriate amount of salt can improve the effective utilization rate of carbon and nitrogen and phosphorus in soil, and result in higher yield for crops. The fruit set is the highest under brackish water irrigation with 3 g/L salt.

Modeling and assessing feasibility of long-term brackish water irrigation in vertically homogeneous and heterogeneous cultivated lowland in the North China Plain

In the North China Plain (NCP), increased water shortages and food yield increase present serious threats to the sustainability of cultivated lands. Irrigation by brackish or saline water is a possible solution to alleviate freshwater shortages. It is critical to understand the soil salt variations and the characteristics of salt accumulation and leaching under long-term brackish water irrigation in cultivated croplands. In this study, the HYDRUS-1D model was calibrated and validated, and then applied to evaluate that how 20 years of irrigating with brackish water affects soil salinity and soil salt transport in wheat-maize cultivated lands with different texture layers in the lowland of NCP. The results showed that the simulations of soil matric potential and soil salt concentrations fitted well with the measured values. Soil salt dynamics were dominated by seasonal precipitation and hydrological years. Seasonal rainfall distribution determined seasonal characteristics of salt changes in shallow layers (0–100 cm). Soil salt accumulated during the growth period of winter wheat corresponding to the dry season, and was greatest at the harvest. Soil salt leached down to deeper soil layers under abundant rainfall during growth period of maize. The annual soil salt in 300 cm profiles were driven by hydrological years, and soil salt could be accumulated in dry and normal years and leached in wet years, especially in the extremely wet year. Soil salt accumulation was higher under two brackish water irrigations compared to one irrigation for winter wheat, and soil salinity in homogeneous soils was less than in the heterogeneous soil with clay loam interlining. The results showed the effect of irrigation times of brackish water was greater than that of soil texture on soil salt accumulation. Our results demonstrated that wheat and maize could be grown well under one irrigation with brackish water a year. Salt accumulation increased with the number of irrigation events that used brackish water for winter wheat. The brackish water irrigation was evaluated and the results demonstrated that partial substitution of fresh water by brackish water for irrigation is feasible in the lowland area of the NCP. It is more suitable for long-term brackish water irrigation in relatively homogeneous soil than in heterogeneous soil. These simulated results are helpful to provide appropriate management measures for long-term brackish water irrigation and fresh water saving, and provide a basis for assessing the environmental effect under long-term brackish water irrigation.

Social and private costs of water for irrigation: The small desalination plant in San Vicente del Raspeig, Spain

Among non-conventional water resources, desalination (from seawater or brackish aquifers) has emerged as a feasible option to deal with water shortage in arid and semi-arid areas. At the University of Alicante (UA, SE Spain), water availability is lacking and groundwater quality is poor. To ensure water availability, the UA built a small reverse osmose (RO) desalination plant (450 m3/day) to water the green areas and an urban park on the campus. The costs of a small private desalination plant, landscape irrigation, and the full cost of water, were assessed. This assessment considered the benefits made by new green areas existing in an urban space and citizens’ willingness to pay (WTP) for its preservation based on the contingent valuation method (CVM). The results indicated that the final desalinated brackish water cost was 0.29 €/m3 and, according to the WTP results, the value that derived from the social benefits provided by the leisure area was 0.51 €/m3, being the final cost of water 0.22 €/m3. Consequently, the use of brackish water for irrigation has a high social value that should be considered when evaluating desalination-related projects.

Optimization model for on-farm irrigation management of Mediterranean greenhouse crops using desalinated and saline water from different sources

Desalination is becoming a competitive alternative for supplying quality water to irrigation districts in dry areas. However, its acceptance level among farmers is often low due to its higher price, the need for additional fertilization, and the misconception that it would negatively affect yield and crop quality. This work presents a decision support system that would help them to make irrigation management decisions regarding the optimal combination of saline and desalinated seawater (DSW), which would provide maximum economic profit. The model has been specially designed for Mediterranean greenhouse cropping systems. The proposed model was validated by applying it to a real watermelon crop which was experimentally monitored. A sensitivity analysis was then conducted in order to analyze the effect of different limiting factors on the optimal combination of water and the optimal profit for farmers.The application of the model to the case study demonstrated that it is profitable to use a blend of DSW and brackish water for irrigation of greenhouse crops. Despite the higher cost of the DSW, the economic optimum was achieved for higher DSW fractions than those which are used today. This sensitivity analysis has demonstrated that brackish water salinity, irrigation uniformity and crop tolerance are relevant factors that affect the optimal combination decisions. This work may encourage farmers to accept desalinated water.

Effect of brackish water irrigation on soil degradation and performance of salt tolerant wheat and maize genotypes

A field experiment was conducted to study the effect of brackish water on soil physical and chemical conditions and yield of wheat and maize genotypes at the farmers’ field. Two salt tolerant genotypes for each crop were selected from previous hydroponic and lysimeters studies. Wheat-maize cropping system was followed using tubewell brackish water alone and with chemical (gypsum) and organic (FYM) amendments. The results revealed that treatments have significant effect on all growth and yield parameters and followed the trend of T1>T3 >T4 > T2. Highest grain yield of wheat genotypes (SARC-1 & V-8670) was observed in control (4050 & 3800 kg/ha) and lowest was in T2 (2862 & 2200 kg/ha). Similar trend was observed in maize fodder yield that was 9625 & 8875 kg/ha in control and 4350 & 2253 kg/ha in T2 for Sahiwal-02 and Akbar, respectively. Maximum reduction in wheat grain and maize fodder yield observed in T2 (tubewell water alone) where high EC, SAR and RSC water was applied that was 39 & 57% for 1st year (wheat crop) and 89 & 74% for 2nd year (maize crop) respectively. Data revealed that use of gypsum and FYM along with brackish water improved the wheat grain yield and maize fodder as compared to T2. More adverse effect of brackish water was observed in high EC, SAR and RSC treatment (tubewell water alone) as compared to other treatments. Application of amendments (gypsum and FYM) along with brackish tubewell water reduced adverse effect of brackish water. Among genotypes SARC-1 and Sahiwal-2002 performed better in all treatments and textures especially under brackish water treatments.Bangladesh J. Agril. Res. 42(4): 693-705, December 2017

‘Superior Seedless’ grapevine grafted on three rootstocks grown on calcareous soil under diluted brackish water irrigation. III. Stomatal resistance

ABSTRACTGrapevine rootstocks that can be irrigated with diluted brackish water without any adverse effects on grapevine performance are a suitable approach for areas suffering scarce water resources. Stomatal resistance of ‘Superior Seedless’ grafted on three rootstocks, irrigated with different levels of diluted brackish water, was evaluated and correlated with some growth parameters. ‘Superior Seedless’ grafted on 1103P showed less stomatal resistance as compared to 110R and 41B. Ratios of ‘Superior Seedless’ leaf fresh and dry weights to leaf area were not significantly different among the rootstocks. However, ‘Superior Seedless’ grafted on 1103P showed better performance regarding chlorophyll content, shoot length and growth following bud break.

Potential of Solar-driven CDI Technology for Water Desalination in Egypt

Freshwater scarcity is one of the most challenging problems facing the world today. Rivers, lakes, and surface ice represent only 1.2% of the fresh water sources on earth, while ground water represent over 30% of the potential fresh water. The Egyptian quota from the Nile River is limited to 55 billion m 3 /yr, and expected to decrease due to increasing demand of water by other Nile basin countries. According to an Egyptian government report, the total population of Egypt increased from 22 million in 1950 to around 85 million in 2010. This increase in population growth will continue for decades and it is likely to increase to between 120-150 million by 2050. Egypt has reached a state where the quantity of water available is imposing limits on its national economic development. As indication of water scarcity, Egypt passed the international threshold value of 1000 m 3 /capita/year in the nineties, and it is expected to cross the threshold of absolute water scarcity of 500 m 3 /capita/yr by 2025. Capacitive de-ionization (CDI) is a relatively new technology that was developed as recently as the late 1960s. In CDI systems, saline water is made to pass between a pair of electrodes connected to a voltage source. Ions are stored inside the pores of electrodes in CDI via the applied electric field strength. CDI is a membrane less technology, and the problems of membrane fouling in the Reverse Osmosis technology is not present in CDI. It has the potential to be energy efficient compared with other related techniques, robust technology for water desalination. This paper explores low cost and efficient desalination technologies for brackish water for irrigation and drinking purposes using the abundant solar energy in Egypt.

Spatial distribution of soil moisture, soil salinity, and root density beneath a cotton field under mulched drip irrigation with brackish and fresh water

Root systems play a vital role in soil-plant interactions. The dynamics and distributions of soil moisture content (SMC), soil salinity, and cotton (Gossypium hirsutum L.) root density under mulched drip irrigation are complex and their interactions are not well understood. The aim of this study is to describe these dynamics and distributions and to evaluate their impacts on cotton above-ground growth and yield during two-year field experiments in a cotton field under mulched drip irrigation with brackish and fresh water. Significant differences were observed for the distributions of SMC, soil salinity, and root length density (RLD) in the root zone for brackish water irrigation treatment (BWT) and fresh water irrigation treatment (FWT). The average SMC and soil salinity in the root zone were higher for BWT than for FWT. The spacing of irrigation lines also had measurable impacts. SMC was less variable when irrigation spacing was small (narrow rows) than beneath wide rows. SMC for BWT and FWT decreased after irrigation due to root water uptake; simultaneously, salt concentration increased, especially in regions where RLD was relatively high. More roots were observed growing in the mulched narrow and wide rows than in the no-mulch zone. Roots were concentrated in the shallowest 30cm. Our study indicated that the average values of the ECe (electrical conductivity of soil saturation extract) in the root zone after BWT irrigation were higher than the published threshold value for optimal cotton yield. The average RLD, shoot dry weight and yield for BWT were observed to be lower than those of FWT as a result of the elevated soil salinity associated with BWT.

HYDRUS Simulation of Sustainable Brackish Water Irrigation in a Winter Wheat-Summer Maize Rotation System in the North China Plain

Freshwater resources in the North China Plain (NCP) are near depletion due to the unceasing overexploitation of deep groundwater, by far the most significant source of freshwater in the region. To deal with the deepening freshwater crisis, brackish water (rich but largely unused water in agriculture) is increasingly being used in irrigation in the region. However, inappropriate irrigation with brackish water could lead to soil salinization and cropland degradation. To evaluate such negative impacts, the HYDRUS-1D model was used to simulate soil salt transport and accumulation under 15 years of irrigation with brackish water. The irrigation scenarios included brackish water irrigation during the wintering and jointing stages of winter wheat and then freshwater irrigation just before the sowing of summer maize. Freshwater irrigation was done to leach out soil salts, which is particularly vital in dry years. For the littoral region of the plain, HYDRUS-ID was used to simulate the irrigated cropping system stated above for a total period of 15 years. The results showed that it was feasible to use brackish water twice in one year, provided freshwater irrigation was performed before sowing summer maize. Freshwater irrigation, in conjunction with precipitation, leached out soil salts from the 100 cm root-zone depth. The maximum salt accumulation was in the 160–220 cm soil layer, which ensured that root-zone soil was free of restrictive salinity for crop growth. Precipitation was a critical determinant of the rate and depth leaching of soil salt. Heavy rainfall (>100 mm) caused significant leaching of soluble salts in the 0–200 cm soil profile. Salt concentration under brackish water irrigation had no significant effect on the variations in the trend of soil salt transport in the soil profile. The variations of soil salinity were mainly affected by hydrological year type, for which the buried depth of soil salt was higher in wet years than in dry years. The study suggested that 15 years of irrigation with brackish water is a reliable and feasible mode of crop production in coastal regions with a thick soil column above the water table. The scheme proposed in this study allowed the use of brackish water in irrigation without undue salinization of the crop soil layer, an intuitive way of resolving the deepening water crisis in the NCP study area and beyond.

An Investigation into the Effects of Temperature Gradient on the Soil Water–Salt Transfer with Evaporation

Temperature gradients exist in the field under brackish water irrigation conditions, especially in northern semi–arid areas of China. Although there are many investigators dedicated to studying the mechanism of brackish water irrigation and the effect of brackish water irrigation on crops, there are fewer investigations of the effects of temperature gradient on the water–salt transport. Based on the combination of a physical experiment and a mathematical model, this study was conducted to: (a) build a physical model and observe the redistribution of soil water–heat–salt transfer; (b) develop a mathematical model focused on the influence of a temperature gradient on soil water and salt redistribution based on the physical model and validate the proposed model using the measured data; and (c) analyze the effects of the temperature gradient on the soil water–salt transport by comparing the proposed model with the traditional water–salt model in which the effects of temperature gradient on the soil water–salt transfer are neglected. Results show that the soil temperature gradient has a definite influence on the soil water–salt migration. Moreover, the effect of temperature gradient on salt migration was greater than that of water movement.