Saline-sodic Water Research Articles

Salinity and sodicity influences on infiltration during surge flow irrigation

The interactive influences of water quality and surge-flow irrigation (intermittent application of water) on infiltration into a bare loam soil, packed into a long metal flume, were measured with a laboratory recirculating infiltrometer devised for the experiments. Cumulative infiltration and final infiltration rates were measured over three irrigation episodes using synthetic waters of different qualities. Four water-quality combinations of low and high salinity levels (i.e., electrical conductivity, EC=1.5 and 7.5 dS/m) and low and high degree of sodicity [i.e., sodium adsorption ratio in the range of 5–10 and 25–35 mmol1/2 l–1/2] were tested. Results showed that surge-flow cumulative infiltration of low saline waters – especially during the first irrigation episode – was lower than the corresponding continuous-flow cumulative infiltration. Conversely, it was higher for high saline and high saline-sodic waters. Effects of the water-quality treatments on final infiltration rate were similar to and in agreement with the effects on cumulative infiltration. However, the range of the final infiltration rates among surge-flow treatments was larger than with the continuous-flow treatments. Overall, infiltration was higher with surge-flow application of high saline and high saline-sodic waters than with the continuous-flow treatment. The observed contrasting results for the surge effect with the low saline, high saline, and high saline-sodic water-quality treatments were attributed to soil consolidation, formation of a depositional seal layer, and the different levels of irrigation water salinity and sodicity. It was concluded that the "surge effect" phenomena (reduction in soil infiltration caused by surge flow) under brackish (saline, sodic, and saline-sodic) water application was not pronounced and had adverse effects, in comparison to the low saline-sodic water application. Consequently, from theory, practical application of surge-flow irrigation under these circumstances, from viewpoints of infiltration reduction and irrigation efficiency improvements, is questionable.

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 (Ca 2+) that can replace the excess exchangeable sodium (Na +). Most of these soils, however, contain calcite (CaCO 3) of extremely low solubility. The native calcite does not supply adequate levels of Ca 2+ 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 CaCO 3 to supply adequate Ca 2+ 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, CaCO 3=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.

Changes in hydraulic conductivity of soils varying in calcite content under cycles of irrigation with saline-sodic and simulated rain water

Soil infiltration problems occur as a result of alternating irrigation with saline-sodic waters and monsoon rainfall. Hydraulic conductivity (K) and related soil properties of a non-calcareous (CaCO3 0.8%) and a calcareous soil (25.7%) having similar textural constituents were monitored. The soils were subjected to six consecutive cycles of irrigation with saline waters (SW) of sodium adsorption ratio (SAR), 10, 20 or 30 (mmol/l)1/2, but of similar electrolyte concentration (EC; 80 mEq/l), and each followed by simulated rain water (SRW) (electrical conductivity <0.02 dS/m). Results are presented in terms of relative K i.e. K r=K sw/K tw where K tw is steady state K measured separately under application with tap water (ECw 0.54 dS/m, SAR 0.9). For irrigation with SW alone, K r values were reduced to 0.95, 0.79 and 0.70 at SAR of 10, 20 and 30, respectively, in non-calcareous soil. The corresponding values of 0.95, 0.87 and 0.79 were slightly higher in calcareous soil. Severe reductions in K r were observed in both the soils when subjected to alternate use of SW and SRW (K r=0.22, 0.03 and 0.02 in non-calcareous, and 0.57, 0.17 and 0.07 in calcareous soil). About half of the reductions in K r were reversible when SW was subsequently applied. Depth distributions of salinity, pH, dispersible clay and hydraulic head indicate that disaggregation and dispersion of surface soil was the cause of reduced K with SRW, whereas “washed in” sub-soil became restrictive and controlled the K values with SW under alternations of SW and SRW. Salt release (<1 mEq/l) was insufficient to avoid dispersion and sustain K even in the calcareous soil. For evaluating the infiltration hazard of saline-sodic water, measurements of stabilized K values after consecutive cycles of SW and SRW should serve as a better diagnostic criteria under monsoonal climates than threshold EC–SAR combinations.

Effects of soil salinity from long-term irrigation with saline-sodic water on yield and quality of winter vegetable crops

From 1988 onwards a study was carried out to evaluate the long-term effects of increasing water salinity (0%, 0.125%, 0.25%, 0.5% and 1% of commercial NaCl) on some vegetable crops growing in a clay-loam soil. In 1992 and 1993 the effects of the residual soil salinity on yield and some aspects of yield quality were studied in lettuce, endive and fennel grown during irrigation-free seasons on a field which had undergone the same irrigation treatment since 1988. Within the range of electrical conductivity of the saturated-soil extract (ECe) between 2.0 dS m −1 (treatment 0%) and 6.0 dS m −1 (treatment 1%) the marketable yield decreased by about 60% in endive and fennel and by about 15% in lettuce which proved more tolerant than the other crops. Gas exchange rates and stomatal conductance were reduced by salinity in lettuce. Soil salinity affected product quality: lettuce and endive appeared to be more sensitive to tipburn and necrotic symptoms occurring in the crop under saline-sodic conditions; fennel heart length, width, and thickness were also significantly reduced and the heart shape tended to be modified in plants grown on salt-affected plots. The results, obtained by analyzing the salt tolerance model of Maas-Hoffman and its descriptive parameters, place lettuce, endive and fennel in the moderately sensitive category. In terms of ECe, the threshold ranged from 1.8 dS m −1 (fennel) to 2.7 dS m −1 (lettuce) while the slope varied between 5.8% per dS m −1 (lettuce) and 15.7% per dS m −1 (endive).

Polymer effects on runoff and soil erosion from sodic soils

High levels of soil sodicity, resulting from intensive irrigation with saline-sodic waters, lead to an increased soil susceptibility to seal formation and to severe problems of runoff and soil erosion. The objective of this study was to investigate the efficacy of the addition of small amounts of an anionic polyacrylamide (PAM) to the irrigation water in controlling seal formation, runoff and soil erosion. Two predominantly montmorillonitic soils were studied, a grumusol (Typic Haploxerert) and a loess (Calcic Haploxeralf), having naturally occurring exchangeable sodium percentage (ESP)>12. The soils were exposed to 60 mm of simulated irrigation with commonly used tap water (TW, electrical conductivity=0.8 dS m−1; sodium adsorption ratio (SAR)=2), or saline water (SW, electrical conductivity=5.0 dS m−1; SAR>12). PAM effectiveness in controlling runoff and erosion from the sodic soils was compared with runoff and erosion levels obtained from untreated soils having low ESPs (<4). For both soils and for both water qualities and polymer concentrations in the irrigation water, PAM was efficient in controlling runoff at low ESP levels and inefficient at high ESP levels. At moderate ESP levels, PAM's efficacy in controlling runoff was inconsistent and varied with water quality and polymer concentration. Conversely, in general, soil loss originating from rill erosion, was significantly and effectively reduced in moderate and high ESP soils by addition of PAM to the irrigation water, irrespective of water quality and polymer concentration. PAM was more effective in reducing rill erosion than in reducing runoff in the moderate and high ESP samples, because the energy involved in generating runoff is much higher than that involved in rill erosion. PAM treated surface aggregates were not stable against the distructive forces leading to seal formation and runoff production; but they were stable enough to resist the hydraulic shear exerted by the runoff flow.

Effect of frequency of sodic and saline-sodic irrigations and gypsum on the buildup of sodium in soil and crop yields

The effect of three frequencies of irrigation with sodic (high residual alkalinity) and saline-sodic (high residual alkalinity and high NaCl concentration) waters in presence and absence of gypsum application on soil properties and crop yields were investigated under millet (fodder) — wheat — maize (fodder) rotation in a field experiment carried out for 6 years (1986–1992) on a well drained sandy loam Typic Ustochrept soil. Irrespective of the irrigation intervals, sustained use of sodic and salinesodic waters increased pH, electrical conductivity and ESP of the soil and hence significantly decreased crop yields. Application of gypsum decreased ESP and significantly improved crop yields. The beneficial effect of gypsum was lower under saline-sodic irrigation. There were no significant beneficial effects of increasing the frequency of sodic and saline-sodic irrigation, both in presence and absence of applied gypsum, on the yields of wheat and millet (f) crops grown during winter and monsoon seasons, respectively. But decrease in irrigation interval significantly improved yields of maize (f) grown during the hot dry summer period. Frequency of irrigation did not appreciably alter the effectiveness of applied gypsum in wheat and millet (f) but in maize (f), the gypsum treatment was more effective under more frequent irrigation.

Irrigation and sodicity

The productivity of irrigated agriculture in Australia is low for most crops and one important factor is the physical and chemical constraints caused by sodicity in the rootzone. Over 80% of the irrigated soils are sodic and have degraded structure limiting water and gas transport and root growth. Irrigation, without appropriate drainage, leads to the buildup of salts in soil solutions with increased sodium adsorption ratio (SAR) and can develop perched watertables due to a very low leaching fraction of the soil layers exacerbated by sodicity. Therefore, irrigation management in Australia is closely linked with the management of soil sodicity.The inevitable consequence of continued irrigation of crops and pastures with saline-sodic water without careful management is the further sodification of soil layers and concentration of salt in the rootzone. This will increase the possibility of dissolving toxic elements from soil minerals. The yields of crops can be far below the potential yields determined by climate. The cost of continued use of amendments and fertilizers to maintain normal yields will increase under saline-sodic irrigation. Most of the irrigated soils in Australia need reclamation of sodicity of soil layers at least in the rootzone. The management of these sodic soils involves the application of gypsum, suitable tillage and the maintenance of structure by the buildup of organic matter and biological activity aver time. Then artificial drainage, an essential component of the management of irrigated sodic soils, is possible. By following these soil management practices, irrigated agriculture in Australia will become sustainable with increased yields and high economic returns.

Effect of continuous irrigation with sodic and saline-sodic waters on soil properties and crop yields under cotton-wheat rotation in northwestern India

A field experiment was conducted for 8 years (1983–1991) on a well-drained sandy loam Typic Ustochrept soil involving sodic (NaHCO 3) and saline-sodic (NaHCO 3 + NaCl) irrigation waters under cotton-wheat rotation. Soil pH and exchangeable sodium percentage (ESP) increased with increase in residual sodium carbonate (RSC) and SAR of the irrigation water. The build up of salts and ESP was considerably higher under saline-sodic irrigation treatments. From amongst the empirical equations used for predicting the sodicity hazards of irrigation waters, the Rhoades equation could fairly accurately predict the build up of ESP for sodic waters containing mainly NaHCO 3. The modified Ayers and Westcot equation predicted the ESP for all the sodic waters and also for the saline-sodic waters with high RSC values. For the waters with high SAR values due to a high NaCl concentration and low RSC values, none of the models could predict the build up of ESP. Under the cotton-wheat rotation, irrigation waters with high RSC values decreased the crop yields considerably more than irrigation waters with low RSC and high SAR values. The decrements in the yields of both wheat and cotton crops were almost similar under increasing levels of RSC in irrigation water.

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.

Hydraulic conductivity and clay dispersion as affected by application sequence of saline and simulated rain water

Saturated hydraulic conductivity HC, and degree of clay dispersion DD, were determined for a sandy loam and a clay loam soil with waters of different combinations of sodium adsorption ratios SAR (5, 15, 30 and 45 mmol1/2l−1/2) and total electrolyte concentration TEC (15, 30, 60 and 90 me l−1) followed by distilled water to simulate rainwater. Increase in SAR and decrease in TEC of leaching water increased DD and decreased HC of soils. The HC values were more highly correlated with SAR than TEC. The critical ratio of TEC/SAR of water below which the relative HC is less than the ‘hreshold’ value (i.e. ≦ 0.75) was 3.82 and 2.01 for clay loam and sandy loam, respectively taking the HC of initial soil with good quality water (SAR = 0.5, EC = 0.3dS m−1) as the reference. Drastic reductions in conductivity were observed even at SAR = 5 (60–83%) when saline water was displaced by rainwater, sensitivity being greater for the sandy loam than for the clay loam; recovery was negligible when the saline water was again applied. Data of EC and clay content of the effluent on application of distilled water suggested that clay dispersion, its movement and lodgement into conducting pores, may be the major cause of HC reduction in sandy loam, whereas in clay loam, surface sealing is the major cause. With distilled water application HC values were governed by SAR rather than TEC of initial water used. The study thus suggests that existing water quality criterion may underestimate the real soil permeability hazards from saline-sodic waters during rainfall infiltration in monsoon season.

Drip irrigation of cotton with saline-sodic water

A two-year study was conducted in the Negev region of Israel, using the drip method, to determine the effect of four levels of water quality (EC =1.0, 3.2, 5.4 and 7.3 dS/m) in combination with three soil amendment treatments (gypsum spread on the soil surface along the drip laterals after planting, injection of H2SO4 into the water during each irrigation, and a control) on plant response, salt distribution in the soil profile, and soil sodification processes. Salinity did not reduce yields even at the highest level, in spite of sodium and chloride accumulation. The highest seed cotton yield (6.4 t/ha) was obtained with the local well water (EC =3.2 dS/m), indicating an optimal response to salinity. The addition of soil amendments during the irrigation season, although reducing exchangeable sodium accumulation near the emitter, endangers the next crop by increasing sodium accumulation under the plant row. It is therefore, recommended that the amendment be applied only before the winter.

Effects of Tillage and Gypsum Incorporation on Rain Runoff and Crust Strength in Field Soils Irrigated with Saline-Sodic Water1

The effects that two tillage-gypsum incorporation patterns have on rain runoff and crust strength were studied in two fields irrigated with saline-sodic water (EC − 5.8 mmho cm−1, SAR − 18) and fresh water (EC − 0.95 mmho cm−1; SAR − 2.6). Leaving the soil surface rough (without ridging) reduced runoff to a minimum (3%) compared with other ridging patterns, where up to 40% of the rainfall per storm may be lost regardless of the direction of the ridge in respect to the area gradient or to gypsum application. The experiments were carried out in adjacent fields having a general slope of 1% and an annual mean rainfall of 371 mm.

SALINITY EFFECTS ON HYDRAULIC PROPERTIES OF SOILS

Laboratory determinations of saturated hydraulic conductivity and infiltration rate were conducted with four soils varying in texture from sand to clay and with five saline-sodic waters. The waters varied in total dissolved solids from 1250 to 15000 milligrams per liter and in SAR from 16 to 57 and were representative of saline groundwaters in New Mexico. Saturated hydraulic conductivities of the soils were not significantly affected by water quality if these waters were the sole source of irrigation water. Nevertheless, even small additions of high-quality water (“rains”) to soils previously equilibrated with the saline-sodic waters significantly decreased soil permeability. Dispersion and short- or longdistance transport of clay apparently clogged conducting pores when “rain” was introduced. Swelling was an important mechanism in reducing soil permeability only in the clay soil. The data suggest that, when saline-sodic water is the dominant irrigation source and is supplemented by “rains,” (1) all waters could be used on very sandy soils, (2) no saline-sodic waters should be used on fine-textured soils, and (3) slightly sodic, but not highly sodic, waters could be used on medium-textured soils.