Soil Exchangeable Sodium Percentage Research Articles

Unsaturated flow of different quality irrigation waters through clay, clay loam and silt loam soils and its dependence on soil and solution parameters

The effect of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of irrigation water on unsaturated hydraulic properties, viz. unsaturated hydraulic conductivity, wetting front advancement and soil-water diffusivity of clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Haplorthent) soil was studied in a laboratory experiment. Twenty-four types of irrigation waters, encompassing four TEC levels, viz. 5, 10, 20 and 50 me l −1 and six SAR levels, viz. 2.5, 5, 10, 15, 20 and 30 m mol 1/2 l −1/2 were synthesised to equilibrate the soil samples using pure chloride salts of calcium, magnesium and sodium at Mg:Ca=1:2. Unsaturated hydraulic conductivity ( K θ ), was determined both directly (by ‘inflow–outflow’ vertical infiltration method for water potentials of −5 and −10 kPa) and indirectly (from diffusivity functions and soil-water retention curves) in two different water potential ranges. Wetting front advancement and diffusivity ( D θ ) were determined by the horizontal infiltration method. Water quality had larger impacts on the unsaturated hydraulic conductivities of the silt loam soil than on the clay and clay loam soils. The effects of TEC and SAR were both large for the silt loam soil whereas the effects of SAR were predominant for the clay and clay loam soils. At a water potential of −5 kPa (50 cm suction), the hydraulic conductivity of clay and clay loam soils was approximately 10 times smaller than at saturation under different quality waters. However, the hydraulic conductivity of silt loam soil was approximately 10 and 100 times smaller than at saturation for low SAR (up to 10 m mol 1/2 l −1/2) and high SAR (15 m mol 1/2 l −1/2 and above) waters, respectively. Influence of irrigation water quality on K θ increased with decreasing water content. SAR of water and exchangeable sodium percentage (ESP) of soils influenced K θ significantly. Besides SAR, TEC also influenced K θ of silt loam significantly. D θ increased with increase in TEC and/or decrease in SAR of water. The clay soil was found to be the most sensitive soil to unsaturated flow above SAR 15 m mol 1/2 l −1/2. At higher and lower water contents, the dependence of D θ on SAR of water and ESP of soil was found to be highly significant. However, in silt loam soil it was significantly dependent on TEC of water also.

Effect of soil type, exchangeable sodium percentage, water content, and organic amendments on urea hydrolysis in some tropical Indian soils

Urea has emerged as one of the most extensively used sources of nitrogen fertiliser in recent years because of its low cost per unit nitrogen. Urea hydrolysis in soils is an enzymatic decomposition process by the enzyme urease. The effects of soil type, exchangeable sodium percentage, moisture regime, and organic manures and their levels on the kinetics of urea hydrolysis were studied in a series of laboratory incubation experiments at 25 ± 1�C. Urea transformation followed first-order kinetics, and the first-order rate constants for soils varied from 0.0321 to 0.1182/h. The rate of urea hydrolysis in the different soils increased with greater clay content and followed the order: Gulkani clay loam > Dadupur loam > Hisar sandy loam > Jakhol silty clay loam > Bawal loamy sand > Balsamand sand. Increasing the exchangeable sodium percentage in soils decreased the rate of urea hydrolysis both at field capacity and flooded conditions (2 cm standing water). Application of vermicompost, sheep manure, poultry manure, pig manure, and urban waste to soil at the 1% level increased the rate of hydrolysis over the untreated soil.

English

Cattle grazing is a potential post-mining land-use option for open-cut coal mines in the dry sub-tropical region of central Queensland, Australia, but no research has been conducted to determine the grazing capacity of these lands. A study was conducted to develop a model for estimating pasture productivity of rehabilitated mined lands, from which long-term sustainable stocking rates could be predicted. Rainfall-use efficiency (RUE), a reliable indicator of pasture productivity in this moisture-limited environment, was calculated for 17 plots across three minesites over a single growing season, and related by linear regression and stepwise multiple linear regression to several site and mine-soil properties. Plots were dominated by Cenchrus ciliaris (buffel grass), and ranged in age from 3 to 25 years since establishment. Slope (r 2 =0.45) and surface cover (r 2 =0.44) were most strongly correlated with RUE. These factors were interpreted as affecting surface retention of rainfall. The factors most correlated with RUE from multiple linear regression were slope (r 2 = 0.45), surface soil exchangeable Mg (cumulative r 2 = 0.71) and surface exchangeable sodium percentage (ESP) (cumulative r 2 = 0.77). ESP is a measure of soil dispersion and surface crusting, which when combined with slope (negative correlation), influenced the ability of incident rainfall to enter the soil profile. Mg was interpreted as a surrogate soil fertility factor, as Mg was strongly correlated with soil total N (r 2 =0.53) and cation exchange capacity (r 2 =0.74). Dry matter yield and RUE results are generally consistent with those observed on unmined pastoral lands in the region, but data from additional sites and over more seasons are required to fully develop and validate the model for minesite conditions.

Irrigation of grapevines with saline water at different growth stages. 1. Effects on soil, vegetative growth, and yield

Mature field-grown grapevines, Colombard on Ramsey rootstock, grown in a semi-arid climate were irrigated with saline water during any one of 4 growth stages within the season: pre-flowering, during berry development, during berry ripening, and post-harvest. At other times, plots were irrigated with river water (EC 0.5 dS/m) as was the control throughout the season. Saline water (EC 3.5 dS/m) with a high sodium absorption ratio was produced by addition of sodium chloride brine. Soil cation exchange capacity was 14 cmolc/kg, and at the end of the trial, the soil exchangeable sodium percentage in the control was 6%, in the treatment salinised pre-flowering 13%, during berry development 20%, during berry ripening 20%, and post-harvest 19%. Treatments were applied for 6 consecutive seasons. Vines were highly productive, with the average yield in the control equal to 62 t/ha of grapes. Saline irrigation caused significant, but small, declines in yield in 3 seasons, in pruning weights in 2 seasons, and in berry weights in 4 seasons. Effects on growth, once established, often persisted unchanged through one or more subsequent seasons of saline irrigation. The growth stage shown to be most sensitive to saline irrigation was berry development; saline irrigation during berry development reduced the yield by 7% and during berry ripening by 3%, and pre-flowering it reduced the berry weight by 1%, during berry development by 6%, and during berry ripening by 4%. The amounts of irrigation applied in each of the 4 growth stages were not equal, and hence, treatments did not receive equal additions of salt. Normalising data to remove this effect showed that the rate of yield decline per unit dS/m increase in the seasonal average salinity during berry development, 7%/dS.m, was 3-fold greater than the 2%/dS.m during berry ripening. We conclude that this scion/rootstock combination, grown under these conditions, can maintain high productivity despite ‘slugs’ of saline irrigation.

Alterações nas propriedades químicas de um solo aluvial salino-sódico decorrentes da subsolagem e do uso de condicionadores

Solos afetados por sais são característicos de zonas áridas/semi-áridas. Este trabalho foi desenvolvido no vale do Açu (RN), no período abril/90 a janeiro/91, objetivando avaliar o efeito do preparo do solo (convencional e convencional + subsolagem) e da aplicação de condicionadores ( gesso, esterco de curral e palha de carnaúba) nas propriedades químicas de um solo aluvial salino sódico. A subsolagem proporcionou efeito eficaz na redução da porcentagem de sódio trocável (PST) e no abaixamento do pH do solo. Nos tratamentos com gesso, foram detectados os maiores valores de cálcio trocável, redução na PST para menos de 15% na camada de 0-0,15 m e aumento na salinidade do solo. O esterco de curral foi benéfico na redução da PST, principalmente quando associado à subsolagem e à gessagem. Existe um desbalanço natural nas relações K:Ca:Mg trocáveis no solo, que se acentua com a gessagem, necessitando de correção potássica para que se atinja o equilíbrio. A proporção entre cátions trocáveis e solúveis no solo ficou entre 13 e 16:1, para cálcio e magnésio, e entre 0,3 e 3,9:1, para o sódio, sendo este o único cátion solúvel que diminuiu com a subsolagem.

Effect of Soil Sodicity on the Growth and Cation Composition of Palmarosa and Lemongrass

ABSTRACT The effects of soil sodicity on the growth, yield, and cation composition of palmarosa (Cymbopogon martinii Roxb. Wats) and lemongrass (Cymbopogon flexuosus Steud Wats) were studied in a pot experiment. The plant height, number of tillers, and herb yield of both species significantly decreased as the exchangeable sodium in soil increased. A 50 percent reduction in herb yield over control was recorded at soil exchangeable sodium levels of 52 and 37 percent, respectively, for palmarosa and lemongrass. Increases in exchangeable sodium percentages of soil enhanced the concentration of sodium and decreased that of potassium, calcium and magnesium in vegetative tissues of both plants as compared with control. Palmarosa was lower in sodium and better able to maintain the potassium to sodium and calcium to sodium ratios in vegetative tissues under sodicity stress than lemongrass. Geranyl acetate content in the oil of palmarosa increased with increases in the soil exchangeable sodium percentage.

Influence of Salinity and Sodicity on Soil Structural and Hydraulic Characteristics

AbstractAn exchangeable sodium percentage (ESP) >15 is traditionally considered to affect soil structural and hydraulic characteristics. Recent investigations show that both this critical value and the concept of critical threshold need reconsideration, because soil degradation often takes place even at lower ESP in dilute solutions, and soil behavior at increasing ESP appears to be a continuum. This study was carried out to analyze the response of two Sicilian Typic Haploxererts to ESP values up to 15, at a low cationic concentration. The investigation was carried out on aggregate stability, rating of soil shrink‐swell potential, and both saturated and unsaturated hydraulic conductivity. The specific purpose was to verify if a critical ESP threshold exists, or if the hypothesis of a continuum behavior is more appropriate. The high‐energy moisture characteristic technique was used for determining aggregate stability, and Brasher's method for the shrinkage characteristic. The constant‐head method was used for determining saturated hydraulic conductivity, and the parameter estimation method based on one‐step outflow experiments for unsaturated hydraulic conductivity. Almost linear relationships were found between the investigated soil properties and ESP, indicating no critical ESP threshold; furthermore, the results obtained indicate that an effective hazard of soil quality degradation can be forecast even in a 2 to 5 ESP range at a low cationic concentration. This is a basic indication for irrigation management aimed to combat and prevent degradation of soil quality.

Seal Formation and Interrill Soil Erosion

AbstractInterrill soil erosion depends primarily on soil detachment by raindrop impact (splash) and the transport capacity of thin sheet flow. Both splash and sheet flow erosion depend on soil surface properties. The purpose of this study was to investigate the effect of seal formation on interrill soil loss. Samples of three soil types — a Typic Chromoxerert, a Calcic Haploxeralf and a Typic Rhodoxeralf — with various naturally occurring exchangeable sodium percentage (ESP) levels were used. The soils were exposed to simulated rain using three different waters: distilled (DW), tap (TW), and saline (SW). The electrical conductivity (EC) of the TW and SW was 0.8 and 5.0 dS m−1, respectively. Seal formation was characterized by the final infiltration rate (FIR) and amount of runoff. Seal formation was enhanced with an increase in soil sodicity and a decrease in water salinity for each soil type. Nearly 70% of the variation in FIR (and seal formation) was explained by water salinity and soil ESP. Most of the variation in soil loss was explained by clay content, soil ESP, and water salinity. With the exception of samples with ESP <5 rained on with DW, soil loss increased linearly with an increase in soil clay content. Seal strength, as inferred from surface pitting by impacting raindrops, decreased with an increase in clay content, and was inversely related to soil erosion.

Sodic soil reclamation with saline water in conjunction with organic and inorganic amendments

Abstract A greenhouse experiment was conducted to evaluate the effect of soil amendments on the growth, yield, and mineral composition of rice and wheat grown in a highly sodic soil (pH 10.6, exchangeable Na+ 95%). The soil amendments were gypsum at 50% gypsum requirement (GR), pyrite 50% GR on equivalent sulfur basis, farmyard manure (FYM) 1%, gypsum 50% GR + FYM1%, pyrite 50% GR + FYM 1%, and control (no amendment). Saline (EC 4 dS m‐1) and nonsaline (EC 0.4 dS m‐1) water was used for irrigation. Irrespective of the amendments used, soil pH and exchangeable sodium percentage (ESP) decreased due to an initial 10 days submergence, and more with saline water. Application of amendments significantly enhanced the yield of both crops and decreased ESP, irrespective of the quality of irrigation water used and followed the order gypsum + FYM > pyrite + FYM > gypsum > pyrite > FYM > control. The magnitude of increase in the yield of wheat was higher as compared to rice following amendments application. Use of saline water resulted in significantly higher yield of both crops. Decrease in soil pH and ESP was greater after rice than wheat, particularly when nonsaline water was used. However, irrigation of wheat with saline water further decreased the soil pH and ESP.

Use Of Waste Gypsum In The Revegetation On Red Mud Deposits: A Greenhouse Study

The disposal of fine bauxite refining residue (red mud) has occupied huge areas of land which remain derelict and subject to wind and water erosion. The major constraints in rehabilitation are the high alkalinity, salinity and sodicity of red mud. This paper describes a greenhouse study to evaluate the use of waste gypsum as ameliorants for red mud. Red mud was amended with gypsum at 0, 2, 5 and 8% (w/w) and its effect on the growth of two grass species, Agropyron elongatum (Tall wheat grass) and Cynodon dactylon (Bermuda grass), was evaluated. Gypsum amendment significantly reduced the pH, electrical conductivity (EC), and Na and Al content of red mud and provided a continuous supply of Ca 2+, which resulted in a lower soil exchangeable sodium percentage (ESP). The improved soil conditions at ⩾5% gypsum amendment significantly increased seedling emergence and dry weight yields. The enhanced plant growth and seedling emergence show significant negative correlations with pH, Al and ESP of soil. Tissue analyses indicated that the availability of P, K, Mg and Ca also increased for ⩾5% gypsum amended red mud, while Na and Fe were less available. Results from the present study indicated that waste gypsum is an effective ameliorant for red mud revegetation and no topsoil amendment is required.

Use of Waste Gypsum in the Revegetation On Red Mud Deposits: a Greenhouse Study

The disposal of fine bauxite refining residue (red mud) has occupied huge areas of land which remain derelict and subject to wind and water erosion. The major constraints in rehabilitation are the high alkalinity, salinity and sodicity of red mud. This paper describes a greenhouse study to evaluate the use of waste gypsum as ameliorants for red mud. Red mud was amended with gypsum at 0, 2, 5 and 8% (w/w) and its effect on the growth of two grass species, Agropyron elongatum (Tall wheat grass) and Cynodon dactylon (Bermuda grass), was evaluated. Gypsum amendment significantly reduced the pH, electrical conductivity (EC), and Na and Al content of red mud and provided a continuous supply of Ca 2+, which resulted in a lower soil exchangeable sodium percentage (ESP). The improved soil conditions at ≥ 5% gypsum amendment significantly increased seedling emergence and dry weight yields. The enhanced plant growth and seedling emergence show significant negative correlations with pH, Al and ESP of soil. Tissue analyses indicated that the availability of P, K, Mg and Ca also increased for ≥ 5% gypsum amended red mud, while Na and Fe were less available. Results from the present study indicated that waste gypsum is an effective ameliorant for red mud revegetation and no topsoil amendment is required.

Cottage cheese (acid) whey effects on sodic soil aggregate stability

Whey applications reduce a sodic soil's exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) and increase its infiltration rate. Whey's effects on aggregate stability (AS), however, have been less well documented. A greenhouse study was conducted to determine: (1) AS response to whey additions, (2) the profile depth to which surface‐applied whey affected AS, and (3) the relationship between AS and SAR for an illitic soil. Greenhouse lysimeters packed with a Freedom silt loam (Xerollic Calciorthid,) received either 0, 25, 50, or 100 mm of whey (equivalent to 0, 253, 505, and 1010 Mg ha‐1 of liquid whey). After drying, the surface 150 mm was removed, mixed, and replaced. Barley (Hordeum vulgae L. ‘Ludd') was then planted and grown to maturity by irrigating weekly. After harvest, AS was measured by wet sieving. A companion field study was conducted to determine the effects of whey applications and flood irrigations on AS. In Declo silt loam (Xerollic Calciorthid,), 2 X 2 m basins received 0...

Coefficients for estimating SAR from soil pH and EC data and calculating pH from SAR and EC values in salinity models

Abstract Data from highly weathered, low pH, sodic Australian soils have been used to develop a method for estimating soil exchangeable sodium percentage (ESP) or soil extract sodium adsorption ratio (SAR) from soil pH and electrical conductivity (EC) data. The method can also be used to calculate soil pH in soil salinity models using SAR and EC values. The pH was calculated as pH = A + (B × SAR1/2)/(1 + C × EC). Rewriting the equations in terms of SAR (or ESP), gives SAR (or ESP)= [(pH ‐ A)(1 + C × EC)/B]2. This study was conducted to determine whether these same methods could be used to predict the pH and SAR values for arid climate soils that are only slightly weathered and are often sodic under natural conditions. Existing pH, EC, and SAR data from Declo loam (coarse‐loamy, mixed, mesic, Xerollic Calciorthids), Freedom silt loam (fine‐silty, mixed, mesic, Xerollic Calciorthids), and Mazuma sandy loam (coarse‐loamy, mixed (calcareous), mesic Typic Torriorthents) were used to calculate the A, B, and C coefficients for the three high sodium soils. Coefficients obtained for a particular soil site were then used to predict pH or SAR of soil samples at additional sites and the correlation between calculated and measured values were determined. The A values for the Idaho soils are about 0.8 greater than those for the Australian soils, which were not completely base saturated. The Australian soils B values were about twice that of the calcareous Idaho soils, and the C values were not significantly different for the Australian and Idaho soils. In both cases the A coefficient values were slightly smaller than or nearly equal to the smallest pH values in a particular data set. Using coefficients from one location of a particular sodic or saline‐sodic soil to predict pH or SAR of the same soil, at a second location, was shown to be practical. Each soil type, however, requires its own set of coefficients. These relationships provide a rapid field method for estimating SAR or ESP from easily obtainable EC and pH data once the A, B, and C coefficients are determined for a particular soil. They also provide a method for pH calculation in soil salinity models that take into account soil EC and sodium effects on pH.

Soil Dispersibility, Rain Properties, and Slope Interaction in Rill Formation and Erosion

AbstractSoil erosion increases with slope steepness. We hypothesized that the rate at which short‐slope soil erosion increases with slope steepness depends on the prevailing erosion mechanism, which in turn depends on soil dispersibility and rain properties (impact energy of drops and water quality). Soil dispersion, as a function of exchangeable sodium percentage (ESP) and water quality, was determined by shaking soil samples in deionized water (DW) or tap water (TW). Clay dispersion increased with increases in soil ESP and was prevented by the electrolyte concentration in TW. We studied the effect of soil ESP, water quality, and the impact energy of rain on soil erosion while maintaining similar runoff. To do so, we first exposed the soil samples to DW rain on a 5% slope until a surface seal developed. Then we increased the slope to 35% and changed the water quality and impact energy of the rain. Runoff volumes were unaffected by rain properties at the 35% slope. Soil losses increased with increases in the ESP of the soil. Soil losses varied with rain properties in the following order: DW rain > TW rain = DW rain with low energy (mist) > TW mist. Rills were formed by both DW rains (high impact energy and mist). The extent of rilling increased with soil ESP. No rills were formed by TW rains. Under dispersive conditions (sodic soils and DW), runoff was sufficient to initiate rilling and soil losses increased sharply with slope.

Stress studies in lentil (Lens esculenta Moench)

The response of soil exchangeable sodium percentage levels to nitrate reductase activity, nitrite reductase activity, free proline, DNA, RNA, chlorophyll a and b contents and yield components in lentil (Lens esculenta Moench)cv. PL 406 was studied in a replicated pot experiment. All the biochemical observations were recorded at four growth stages i.e. 30, 60, 90 and 120 days after sowing (DAS). Germination occurred up to exhangeable sodium percentage of 30, but plants survived only up to 25. With increasing exchangeable sodium percentage, there was a continuous decrease in chlorophyll a and b content, nitrate and nitrite reductase enzyme activities and DNA and RNA content. Increasing level of sodicity enhanced the free proline content up to 60 DAS, after which values fell.

Field Infiltration of a Salt‐Loaded Soil: Evidence of a Permeability Hysteresis

AbstractLow water‐infiltration rates may be detrimental to crop growth by reducing the water available to the plant, limiting salt leaching, and inducing ponding that may result in poor aeration during irrigation. Permeability has been shown to be a function of both the total salinity and the exchangeable sodium percentage (ESP) of the soil. Our objective was to measure the changes in water infiltration that occurred following extended salt loading on a Holtville silty clay (clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent) with permeability problems. An earlier 4‐yr salt‐tolerance experiment provided large plots (6 by 6 m) with six levels of salinity‐sodicity and three replicates. Plots were surrounded by fiberglass barriers and were adequately drained. Colorado River water, with an electrical conductivity (EC) of 0.9 dS m−1, was used to reclaim the plots in a series of small 80‐mm irrigations. Measurements of the salinity and the exchangeable cations of saturated soil extracts were taken before, midway through, and following reclamation. Infiltration rates were measured after 4 h of ponding and were found to differ significantly both during and after salt removal by leaching. The infiltration rates showed a hysteretic effect (delayed reaction) of saline and sodic treatments on soil water permeability. We attributed the effect to the slowly reversible flocculation and deflocculation of clay particles. Final soil ESP data from different treatments indicated that a traditional ESP threshold value may be of limited worth unless past salt history of the soil is considered. Models of hydraulic conductivity should account for this permeability hysteresis. Strategies of reusing saline drainage water may benefit from the hysteretic permeability by allowing high infiltration rates to persist.

Prediction of sustained sodic irrigation effects on soil sodium saturation and crop yields

A field experiment was carried out for 9 years (1979–1988) on a Typic Ustochrept to investigate the possibility of predicting the sustained effect of irrigation waters varying in sodicity on soil Na saturation and crop yields under rice-wheat (R-W) and millet-wheat (M-W) crop rotations. Soil Na saturation increased over the years and the increase was higher under R-W than under M-W rotation. Sodium adsorption ratio ( sar iw), adjusted sar iw and residual sodium carbonate ( rsc) were no suitable indicators of soil exchangeable sodium percentage ( esp). For leaching conditions of the R-W system the empirical equation of Bower et al. was a suitable indicator of esp. For the M-W rotation, the Rhoades equation and the modified Ayers and Westcot equation were suitable indicators of esp. The decline in crop yields with increasing sodicity was more pronounced under the R-W rotation than under the M-W rotation. Using the best-fit quadratic relationships of observed yields and adjusted sar iw for all the 9 years of the study, curves were drawn for predicting the number of years for which irrigation waters varying in sodicity can be used to obtain a desired level of crop yield.

Prediction of exchangeable sodium percentage in soils by mechanistic and layer models

An experiment was conducted in Plexiglass columns ( i d . 5.6 cm) to study depth distribution of adsorbed Na+ in Ca-saturated loamy sand, sandy loam and clay loam soils on percolating different volumes of 0.1M NaCl solution. The exchangeable sodium percentage (ESP) decreased gradually with depth and increased with increase in volume of solution percolated. The depth development of ESP of the soils was computed by using a numerical solution of a one-dimensional convective-dispersive partial differential equation (model I) and a conceptual layer model (model II). To account for the effect of adsorption on cation flow, the slopes of the nonlinear adsorption functions fitted to the normalized adsorption isotherms of Na+ were employed in model I , and the Gapon equation was employed in model II. As the Gapon selectivity coefficient (Kg) is dependent on Na saturation, its values were calculated from the regression equation: Kg = 0.22 + 0.0043SAR (where SAR is the sodium adsorption ratio). Model I overpredicted ESP of loamy sand and sandy loam soils throughout the column depth; the overprediction was more pronounced in the former. The coefficient of determination, calculated on the basis of pooled data of three soils and two solution volumes showed that the accuracy of prediction of model II was considerably higher (r2 = 0.80) than that of model 1 (r2 = 0.54).

Drop Impact Energy‐Soil Exchangeable Sodium Percentage Interactions in Seal Formation

AbstractConstant intensity rain (40 mm h−1) with 3.2‐mm drops falling from 0.25‐, 0.90‐, and 2.63‐m heights and impact energies of 1.8, 7.6, and 18.6 kJ m−3, respectively, was used to produce seals on two soils in 55‐mm deep by 82‐mm diam acrylic cylinders. Soil exchangeable sodium percentage (ESP) was altered to ESP 0 (Casaturated soil), 5, and 10 before rain was applied. Infiltration rate (IR) and hydraulic conductivity (HC) of A horizon material from the Wyman (fine loamy, mixed, thermic Typic Haploxeralfs) and Wyo (fine loamy, mixed, thermic Mollic Haploxeralfs) soils decreased due to formation of soil seals as raindrop energy and ESP increased. The Wyo was more susceptible to sealing than Wyman despite its higher organic C content because of its higher (17 vs. 9%) clay content. Seal formation on Ca‐soils (ESP 0) increased gradually with increasing drop impact energy. Soils with ESP 5 and 10 were more susceptible to sealing at low energy rain than were ESP 0 soils. Relative HC and final IR (FIR) decreased with increasing ESP with all rainfall energies and with the no rain treatment on both soils. Aggregate dispersion by raindrop impact and chemical dispersion by sodicity are two complementary processes leading to seal formation. A 5‐Mg‐ha−1 phosphogypsum treatment applied to the Wyman surface reduced seal formation and maintained HC and FIR near the unrained‐on values for the 1.8 and 7.6 kJ m−3 treatments. The 18.6 kJ m−3 raindrop energy produced a seal on the gypsum treated soil with relative HC and FIR more than four times as high as the untreated Wyman.

Predicting sodification of calcium-saturated soil columns on leaching with sodic waters

SummaryDepth accumulation of exchangeable Na+ was measured in Ca-saturated sandy loam soil columns (length 50 cm; diameter 5 cm) after percolating 500, 1000, 1500 and 2000 ml of 013 M Na+, as NaCl, NaHCO3, Na2SO4 and Na2CO3 solutions. The values of exchangeable sodium percentage (ESP) increased gradually with the increase in the volumes of the solution percolated. Two conceptual layer models, based on whether solutions were added to the topmost soil layer in one lot (M-I) or in splits equal to the saturation deficit (M-II), were used to predict the depth distribution of ESP of soil. The chemical processes considered in the models were the formation of ion pairs and the exchange equilibria of Na+ and Ca2+. The predicted values of ESP were considerably higher for model M-II than model M-I. The consideration of ion-pair formation and the accompanying anion had only negligible effect on the predicted ESP. The model M-II over-predicted the experimental ESP throughout the soil columns, whereas the model M-I under-predicted it for the upper layer(s) and over-predicted for the lower layers. On the basis of average ESP of the whole columns, the less realistic model M-I predicted experimental results better than model M-II. This was attributed to the presence of mobile and immobile zones for the flowing solutions.