Soil Salinization and Management Options for Sustainable Crop Production

Suarez D.L.

S. M. Lesch, D. L. Suarez

A simple algebraic technique is presented for computing the adjusted sodium adsorption ratio (SAR) index. The statistical formula presented in this note facilitates the computation of the adjusted SAR without the use of a look-up table, custom computer software, or the need to compute exact individual ion activity coefficients and complexes. A short data analysis example is also presented that demonstrates the application of this technique.

McNEAL B.L., OSTER J.D., HATCHER J.T.

TO TEST THE EXTRAPOLATION OF SATURATION-EXTRACT ANALYSES TO FIELD-WATER CONTENTS, AND TO PROVIDE A MEANS TO TEST THE PERFORMANCE OF SALINITY SENSORS, SEVERAL METHODS FOR CALCULATING THE ELECTRICAL CONDUCTIVITY (EC) OF MIXED-SALT SOLUTIONS HAVE BEEN DEVELOPED AND TESTED ON SATURATION- EXTRACT DATA FROM 193 SOILS. MOST METHODS WERE BASED ON THE ADDITIVITY OF VALUES FOR INDIVIDUAL-ION EC IN BOTH SINGLE- SALT AND MIXED-SALT SOLUTIONS. UP TO 4--6 MMHO/CM AND UP TO 15--40 MMHO/CM, THE CALCULATED AND MEASURED EC COMMONLY AGREED TO WITHIN PLUS OR MINUS 0.2 AND 1.0 MMHO/CM, RESPECTIVELY, DEPENDING ON THE METHOD USED. A SINGLE THIRD- ORDER POLYNOMIAL FOR EACH ION PROVED SATISFACTORY FOR PREDICTING THE EC OF MOST SINGLE-SALT SOLUTIONS CONTAINING THE ION AND A COUNTERION. THE MAIN EXCEPTIONS WERE SOLUTIONS CONTAINING CA2+ AND SO(SUB 4)2-, MG2+, AND SO(SUB 4)2-, OR BOTH. THE THREE SPECIES WERE SUBSEQUENTLY ALLOCATED TO (CA, MG)SO(SUB 4) AND ASSIGNED A SINGLE EC-CONCENTRATION RELATIONSHIP FOR ALL MIXED-SALT SOLUTIONS. DESPITE THE AGREEMENT BETWEEN CALCULATED AND MEASURED EC FOR SINGLE-SALT SOLUTIONS, CALCULATED VALUES FOR MIXED-SALT SOLUTIONS WERE CONSISTENTLY HIGH ABOVE AN EC OF 3 MMHO/CM. SATISFACTORY AGREEMENT WAS OBTAINED BY APPLYING A CORRECTION FACTOR TO THE VALUES OF EC CALCULATED FROM THE POLYNOMIAL METHOD. GOOD AGREEMENT OF CALCULATED AND MEASURED EC WAS ALSO OBTAINED WHEN EXPONENTIAL OR LINEAR-SEGMENT METHODS WERE USED FOR THE CALCULATIONS. THE TWO LATTER METHODS GAVE LOW VALUES FOR THE EC OF SINGLE-SALT SOLUTIONS, AND HENCE COMPENSATED SOMEWHAT FOR THE TREND TOWARD HIGH EC IN MIXED-SALT SOLUTIONS. THE LINEAR SEGMENT METHOD FOR CALCULATING EC IS SUFFICIENTLY SIMPLE FOR ROUTINE CALCULATIONS WITH A HAND CALCULATOR, BUT BOTH THE EXPONENTIAL AND CORRECTED POLYNOMIAL METHODS ARE BEST HANDLED WITH A DIGITAL COMPUTER. ALL THREE METHODS CONSISTENTLY GAVE MORE ACCURATE RESULTS THAN DID A REGRESSION OF EC ON TOTAL CONCENTRATION. /AUTHOR/

Suarez D.L., Wood J.D., Lesch S.M.

The sodium adsorption ratio (SAR) and salinity criteria for water suitability for irrigation have been developed for conditions where irrigation water is the only water source. It is not clear that these criteria are applicable to environments where there is a combination of rain and irrigation during the growing season. The interaction of rainfall with irrigation water is expected to result in increased sodicity hazard because of the low electrical conductivity of rain. In this study we examined the effects of irrigation waters of SAR 2, 4, 6, 8, and 10 mmol(1/2) L(-1/2) and electrical conductivities of 1 and 2 dS m(-1) on the infiltration rate of two soils with alternating cycles of rain (simulated with a rainfall sprinkler) and irrigation water, separated by drying cycles. The infiltration rate of surface samples from two soils, Kobase silty clay (fine, smectitic, frigid, Torrertic Haplustept) and Glendive very fine sandy loam (coarse-loamy, mixed superactive, calcareous, frigid Aridic Ustifluvent) were evaluated under alfalfa (Medicago sativa) cropped conditions for over 140 d and under full canopy cover. Reductions in infiltration were observed for both soils for SAR above 2, and the reductions became more severe with increasing SAR. Saturated hydraulic conductivity measurements taken from undisturbed cores at the end of the experiment were highly variable, suggesting that in situ infiltration measurements may be preferred when evaluating SAR effects.

Corwin D.L., Lesch S.M., Oster J.D., Kaffka S.R.

Munns R., Tester M.

The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na+ or Cl− exclusion, and the tolerance of tissue to accumulated Na+ or Cl−. Our understanding of the role of the HKT gene family in Na+ exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na+ accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

Letey J., Feng G.L.

A general tend exists toward increasing the salt concentration of surface and ground waters in the arid and semi-arid regions of the world. Quantitative knowledge on the interaction between irrigation management and crop yield is becoming increasingly important as water salinities increase. This information is important to the farmer, water resource managers, and to regulatory agencies that might be considering imposing saline water quality standards for streams specifically designed to be protective of agricultural production. The initial guidelines for managing saline irrigation waters, which are still extensively used, were based on steady-state analyses. Subsequently, with the increased knowledge of the physical–chemical–biological interactions that occur in the soil-water–plant matrix, and the advent of high-speed computers, models have been developed that take into account the dynamic interactions. A comparison between two steady-state models and a transient-state model for the calculated ratio of applied saline water to potential evapotranspiration that produced a specific relative yield of corn (Zea mays L.) revealed that a much lower water application is prescribed by the transient-state model. The effects of rain can be quantified by the transient-state models, and can be approximated by calculating the weighted average water salinity of the rainfall and irrigation waters. The steady-state analyses generally over predict the negative consequences of irrigating with saline waters. Irrigation guidelines based on steady-state analyses should be revised using more advanced knowledge.

Suarez D.L., Wood J.D., Lesch S.M.

Existing irrigation water quality criteria related to sodium and salinity are based primarily on short-term laboratory column studies. These earlier studies measured infiltration or hydraulic conductivity of disturbed soil under continuously saturated conditions. Application of these standards to field conditions is uncertain, as it does not account for wetting and drying conditions, formation of crusts and impact of rain events, etc. In this study we examine water infiltration into loam and clay soils irrigated at EC = 1.0 and 2.0 dS m −1 at SAR of 2, 4, 6, 8, and 10 in a management system with alternating (simulated) rain and irrigation and drying between irrigations. For the loam soil the adverse impacts of sodium on infiltration were evident above SAR 2, while for the clay soil adverse impacts occurred above SAR 4. In both soils the SAR behavior was similar for both EC values, 1.0 and 2.0 dS m −1 , indicating that in this range, EC did not affect infiltration. Reductions in infiltration were evident during both the irrigation and rain events, with lower infiltration, as expected during the rain simulations. These results show a greater sensitivity to SAR than indicated in laboratory column studies and existing water quality criteria.

GOLDBERG S., SUAREZ D.L., GLAUBIG R.A.

We investigated the stability of 34 aridzone toil samples from 15 soil series, using clay dispersion and aggregate stability as structural indexes. The study evaluated clay dispersion and aggregate stability as affected by: pH, electrical conductivity, sodium adsorption ratio, soluble silica, cation

MARION G.M., BABCOCK K.L.

Grattan S.R., Grieve C.M., Poss J.A., Robinson P.H., Suarez D.L., Benes S.E.

Reuse of saline drainage waters is a management option that has been suggested for the San Joaquin Valley (SJV) of California in order to reduce both the area affected by shallow water tables and the volume of drainage effluent requiring disposal. Salt-tolerant forages may play an important role in this strategy, while at the same time producing a food source for sheep and cattle. Crop selection for reuse systems, however, will depend upon production potential under saline-sodic conditions. To identify potentially suitable crops, a controlled study using an elaborate sand-tank system was conducted at the US Salinity Laboratory to evaluate ten promising forage crops irrigated with synthetic drainage waters dominated by Na2SO4 with an EC of either 15 or 25 dS/m each containing 500 μg/L Se and Mo as SeO42− and MoO42−. Forages were cut several times over the year-long duration of the experiment. The forage species tested performed differently in terms of absolute biomass accumulation and biomass production relative to salinity level. Cumulative biomass production of alfalfa (Medicago sativa L.), a relatively salt sensitive crop, was higher than most other forages at moderate salinity. As salinity increased to 25 dS/m, however, cumulative biomass of the alfalfa cultivars were reduced by nearly half whereas biomass of the most salt tolerant grasses was reduced between 0 and 20%. Although most forage species tested showed promise, those that performed particularly well based on biomass accumulation, overall salt-tolerance, and forage quality were ‘Jose’ tall wheatgrass, bermudagrass and ‘PI 299042’ paspalum.

Suarez D.L., Šimůnek J.

Numerous models have been developed for predicting major ion chemistry in the soil zone and in recharge to groundwater. Soils that contain CaCO 3 are prevalent in arid and semiarid regions, as well as in humid and temperate regions that have been glaciated or contain carbonate bedrock. Under these conditions, carbonate-solution reactions and ion exchange are the dominant chemical processes. In this model we couple one-dimensional unsaturated water and solute transport with a major ion chemistry routine and plant water uptake. The model has several unique features, including expressions relating reductions in hydraulic conductivity to chemical factors, prediction of CO 2 partial pressure in the root zone based on a CO 2 production-multiphase transport submodel, kinetic expressions for silicate weathering, calcite precipitation-dissolution, and dolomite dissolution, representation of B adsorption using the constant capacitance model, a new method for predicting cation-exchange selectivity, the option to use Pitzer ion interaction expressions for high ionic strength, and a plant growth submodel that includes water, salinity, and O 2 stress. The chemical submodel considers equilibrium ion exchange, as well as various equilibrium and kinetic expressions for precipitation and dissolution of soil minerals, including gypsum, Mg carbonates, and sepiolite. The use of a predictive submodel for CO 2 production and transport allows for the calculation of CO 2 concentrations with depth and time. This enables us to avoid the assumption of constant CO 2 distribution or constant pH required by previous models. Use of kinetic expressions for carbonate chemistry allows a more realistic simulation of soil and groundwater solution composition as well as simulations of carbonate redistribution and climatic change with time.

Suarez D.L., Rhoades J.D., Lavado R., Grieve C.M.

The adverse effects of exchangeable sodium on soil hydraulic conductivity (K) are well known, but at present only sodicity and total electrolyte concentration are used in evaluating irrigation water suitability. In arid areas, high sodicity is often associated with high dissolved carbonate and thus high pH, but in humid areas high sodicity may be associated with low pH. To evaluate the effect of pH (as an independent variable) on A", solutions with the same SAR and electrolyte level were prepared at pH 6, 7, 8, and 9. Saturated A' values were determined at constant flux in columns packed at a bulk density of 1.5 Mg m'. At pH 9, saturated K values were lower than at pH 6 for a montmorillonitic and a kaolinitic soil. For a vermiculitic soil with lower organic carbon and higher silt content, pH changes did not cause large K differences. Decreases in A" were 1 Contribution from the U.S. Salinity Laboratory, USDA-ARS, U.S. Salinity Laboratory, Riverside, CA 92501. Received 16 Dec. 1982. Approved 9 Sept. 1983. 2 Geochemist, Soil Scientists, and Plant Physiologist, respectively. The permanent address of R. Lavado is Institute de Geomorfologia y Suelos, La Plata, Argentina. not reversible on application of waters with higher electrolyte levels. The results from the K experiments were generally consistent with optical transmission measurements of dispersion. Although anion adsorption was at or below detection limits and cation exchange capacity (CEC) was only slightly dependent on pH, differences in pH effects on A" among soils are likely due to differences in quantities of variable-charge minerals and organic matter. Additional Index Words: sodium adsorption rate, electrolyte concentration, optical transmission. Suarez, D.L., J.D. Rhoades, R. Lavado, and CM. Grieve. 1984. Effect of pH on saturated hydraulic conductivity and soil dispersion. Soil Sci. Soc. Am. J. 48:50-55. T ADVERSE EFFECTS of high levels of exchangeable sodium on the hydraulic conductivity (K) of soils are well established. The onset of reduced K at a given soil exchangeable sodium percentage (ESP) SUAREZ ET AL.: EFFECT OF pH ON SATURATED HYDRAULIC CONDUCTIVITY AND SOIL DISPERSION 51 varies with total electrolyte concentration and soil properties (Quirk and Schofield, 1955; McNeal and Coleman, 1966; Frenkel et al., 1978; Shainberg et al., 198la). Despite these and numerous other studies, the exact levels of ESP and electrolyte concentration at which reductions in K will occur for a given soil still cannot be predicted accurately. In published laboratory column studies, neutral or slightly acidic chloride salt solutions (pH =; 6.0) were normally used with a carbon dioxide partial pressure (Pco2) near atmospheric (10"kPa). The pH values of water in the columns were likely =: 6.0 in the upper portion and 7.5 to 8.0 in the lower portions when CaCO3 was present. Arid and semiarid soils are usually calcareous in the subsurface. Sodic soils in this environment are generally associated with high pH and high dissolved carbonate and bicarbonate concentrations. With such soils, pH values can exceed 10 but are more likely in the range of 8 to 9.5 near the surface. Sodic soils may occur also under acid conditions (pH 1.3 L of each solution was passed through the column. The pH 6 solutions were maintained at pH 6 by bubbling CO2 gas into the 5-L Pyrex solution reservoir. An exit tube at the bottom of the reservoir was placed at the same height as the peristaltic pump to eliminate CO2 degassing during the pumping operation. The pH of the leachate was measured in the U tubes before degassing could occur. Influent and effluent solutions were analyzed for Ca, Mg, Na, and K by atomic absorption, alkalinity by acid titration, and Cl by AgCl titration (Rhoades and Clark, 1978). At the conclusion of the experiment, the columns were separated into 1-cm sections and analyzed for exchangeable cations. For purposes of comparison, the K data were scaled to the initial K(K,) values determined with the 100 mmolc L", SAR 20 solution, or 500 mmolc L~, SAR 40 solution. Based on six replications on the Bonsall soil, SAR 40, pH 9 treatment, log K/Kt standard deviations of 0.08, 0.18, 0.19, and 0.11 were determined for solutions of 250, 100, 50, and 25 mmol,; L", respectively.

Suarez D.L.

The relation between the sodium adsorption ratio (SAR) and pHc derived here predicts SAR of the drainage water (SARdw) better than existing empirical equations. Inaccuracies in SAR estimates from the new relationship can be anticipated by the extent to which the derived conditions are valid. Empirical equations provide no understanding of why they are sometimes inaccurate. Due to the relative insensitivity of SAR to calcium concentrations, SAR predictions of most drainage waters (where Ca ≅ ½ HCO3) are satisfactory when the Ca concentration of the drainage water is assumed to be constant at any fixed PCO2. Prediction of SAR in drainage or soil water in the absence of gypsum precipitation requires knowledge of PCO2, irrigation water composition, HCO3/Ca ratio, and the leaching fraction. SARdw can be simply and accurately calculated from the derived equation and a table accounting for ionic strength and HCO3/Ca ratio.

Shainberg I., Rhoades J.D., Suarez D.L., Prather R.J.

Hossain F.F., Messenger R., Captain G.L., Ekin S., Jacob J.D., Taghvaeian S., O'Hara J.F.

With growing usage and demand for the global freshwater supply, there is an increasing need for technologies that facilitate water conservation and environmental stewardship in irrigated agriculture. Toward this end, recent demonstrations of Internet of Things (IoT) sensors have revealed the value of wireless soil moisture content sensors. However, existing wireless solutions often employ above-ground wireless communication modules that physically interfere with routine farming operations. Underground wireless network solutions are severely challenged by the large radio-frequency (RF) propagation loss through soil. This paper presents a method that overcomes both problems by employing completely buried underground IoT sensors and communication modules with UAS (uncrewed aircraft system) mounted LoRaWAN gateways. The UAS mounted LoRaWAN gateway eliminates the need for any in-field base stations and also allows the LoRa enabled sensors to transmit data over short distances with very low energy. Field tests were carried out using this approach to serve as a proof of concept. The RSSI (received signal strength indicator) demonstrates that the proposed solution has good communication link margin and a significantly larger communication range than is necessary for reliable operation. Moreover, this solution is easy to build, scalable, cost-effective, and can be implemented in a highly power efficient fashion.

Gunday S.T., Tombuloglu H., Anil I., Alagha O., Bozkurt A.

In this work, a novel natural pozzolan-incorporated super-absorbent polymer composites (SAPCs), a potential soil-additive to increase water holding capacity and water use efficiency of soil, was synthesized and characterized. Consequently, barley plants have been grown on the produced SAPCs under (1) well-watered and (2) water-deficient conditions. Results showed that SAPCs could reach the highest theoretical equilibrium swelling capacities of 20,000% and 3260% (wt/wt) in pure water and saltwater. Natural pozzolan (NP) incorporation with super-absorbent polymer improves water absorption capacity and thermal stability. Under the water-deficit condition, the amendment of soil with %1 SAPCs and %1 NP suppressed the reduction of relative water content as 4–8%, while it was recorded as 14% in control plants. These results confirmed that SAPC-amended soil could hold significant amounts of water and release it to plant roots gradually as needed. In conclusion, poly(AA-co-AM)/NP SAPCs can be used as a soil additive to reduce water loss, especially in arid/semi-arid regions.

Alam M., Kruger G., Megdal S.B., Songstad D.

Water, soil, air, and sunlight are integrated components of food production. However, water is unique in that humans have been able to manipulate the supply of water, particularly for agrarian applications. A variety of technological innovations in plant breeding, biotech traits, and agronomic improvements have resulted in improved water use efficiency or engineering breakthroughs that result in increased sustainable irrigation techniques. Common to these innovations is investment in science to discover the solutions to the challenge of feeding the estimated 9.5 billion people expected to be living by the year 2050. Water sustainability will be an important factor that has to be addressed, not just in the USA, but globally. As water availability becomes an even more limiting factor, water legislation, regulation, and policy will play an ever-more important role. Managing the water requirements for food production, urban, recreational, and energy and industrial uses will require policy decisions at various levels of government.

Semiz G.D., Suarez D.L., Ünlükara A., Yurtseven E.