Advance in salinity research
Advance in salinity research
Vegetative bioremediation of calcareous sodic soils: history, mechanisms, and evaluation (Review article by M. Qadir and J.D. Oster, Irrig Sci (2002) 21: 91–101. DOI 10.1007/s00271-001-0055-6).
Chemical amendments have been used throughout the world for almost 100 years to reclaim saline-sodic and sodic soils. Some amendments supply calcium (Ca2+) directly to the soil, which then replaces excess exchangeable sodium (Na+), while others help solubilize calcite (CaCO3) in calcareous soils. Chemical reclamation has become costly for subsistence farmers in developing countries. Amendment costs have increased because of greater usage by industry and reductions in government subsidies to farmers. Laboratory and field research, as well as farmers’ experiences, have shown that calcareous sodic soils can also be reclaimed without the application of amendments through the cultivation of certain salt-tolerant crops. This vegetative reclamation strategy is generally known as bioremediation, phytoremediation, or biological reclamation. The principal contributing mechanisms include: (1) enhanced CO2 partial pressure in the root zone because of root and microbial respiration, which increases the solubility of calcite, and (2) improved soil physical properties due to root growth. Vegetative bioremediation can provide financial benefits from the crops grown which help to support farming operations; to some extent bioremediation is a ‘‘pay-as-you-go’’ option.
Evaluation of soil salinity leaching requirement guidelines (Letey et al. Agricultural Water Management 98 (2011) 502–506).
Water for irrigation is a major limitation to agricultural production in many parts of the world. Use of waters with elevated levels of salinity is one likely option to meet the supply of increased demands. The sources of these waters include drainage water generated by irrigated agriculture, municipal wastewater, and poor quality groundwater. Soil salinity leaching requirements that were established several decades ago were based on steady-state conditions. Recently transient-state models have been developed that potentially can more correctly predict the dynamics of the chemical–physical–biological interactions in an agricultural system. The University of California Center for Water Resources appointed a workgroup to review the development of steady-state analyses and transient-state models, and to determine whether the current recommended guidelines for leaching requirement based on steady-state analyses need to be revised. The workgroup concludes that the present guidelines overestimate the leaching requirement and the negative consequences of irrigating with saline waters. This error is particularly large at low leaching fractions. This is a fortuitous finding because irrigating to achieve low leaching fractions provides a more efficient use of limited water supplies.
Drip irrigation salinity management for row crops (Hanson and May, 2011. UCANR Publication 8447. http://anrcatalog.ucdavis.edu).
Comparison of transient state models that include salinity and matric stress effects on plant yield (Oster et al. Agri. Water Management. Volume 103, January 2012, Pages 167–175).
Transient-state models that account for continually changing salinity and matric stress on crop yields have been developed by several research groups. The objective of this research was to compare the simulated yields of forage corn obtained from a common set of soil and water conditions for ENVIRO-GRO, HYDRUS, SALTMED, SWAP and UNSATCHEM. The physical and hydraulic properties of Panoche clay loam were used. The amounts of water applied weekly, based on the climatic conditions in the San Joaquin Valley of California, ranged from 0.9 to 1.3 times (Kirr) the potential evapotranspiration (PET) of corn. The salinity of the applied water (ECiw) ranged from 0.5 to 6 dS/m which brackets the threshold soil–water salinity of forage corn (Zea mays L.) of 3.6 dS/m. The model simulations were run for sufficient back-to-back crop seasons to establish transient matric and osmotic conditions within the root zone that did not change from one crop season to the next, a quasi steady-state condition. SALTMED simulated lower relative yields (RY) than the other models for all combinations of Kirr and ECiw. For the other models, RY values were similar (within about 7% or less) for ECiw ≤ 3 dS/m for all Kirr values. Plots of RY versus ECiw for HYDRUS, SWAP, and UNSATCHEM approximately paralleled each other except that UNSATCHEM produced higher values. ENVIRO-GRO produced the highest RY where Kirr ≥ 1.1 and ECiw ≤ 2.0 dS/m but decreased more rapidly for greater ECiw. ENVIRO-GRO has plant-based compensation which allows water uptake to meet PET as long as any portion of the root zone is not exposed to matric or osmotic stress that exceed threshold levels. This compensation factor produced higher RY at the lower ECiw values. More rapid decrease in RY with increasing values of ECiw simulated by ENVIRO-GRO is attributed to the assumption that the osmotic and matric stresses are additive, whereas the others assume that they were multiplicative. All the models except UNSATCHEM assume a constant relationship between EC and salt concentration in solution. UNSATCHEM takes into account the effects of the ionic composition and ion concentration on osmotic potential, resulting in higher RY values obtained with this model. Since the chemical composition of irrigation waters are all unique, this aspect of UNSATCHEM poses an important capability in the assessment of osmotic effects on crop yields. We conclude the models provide a valuable resource to assess the utility of moderately saline irrigation waters, for a broad range of transient conditions which include variable crops, precipitation, irrigation water management, and irrigation water salinity. We also highly recommend their use to assess the results obtained in experiments that focus on the responses of crop growth and yield to transient changes in soil water content and salinity.
Accounting for potassium and magnesium in irrigation water quality assessment. J.D. Oster, Garrison Sposito and Chris J. Smith. CALIFORNIA AGRICULTURE, VOLUME 70, NUMBER 2 (http://dx.doi.org/10.3733/ca.v070n02p71); Agricultural Water Management 157 (2015) 59–64.
Abstract: Irrigation with treated wastewater is expected to increase significantly in California during the coming decade as a way to reduce the impact of drought and mitigate water transfer issues. To ensure that such wastewater reuse does not result in unacceptable impacts on soil permeability, water quality guidelines must effectively address sodicity hazard. However, current guidelines are based on the sodium adsorption ratio (SAR) and thus assume that potassium (K) and magnesium (Mg), which often are at elevated concentrations in recycled wastewaters, pose no hazard, despite many past studies to the contrary. Recent research has established that the negative effects of high K and Mg concentrations on soil permeability are substantial and that they can be accounted for by a new irrigation water quality parameter, the cation ratio of structural stability (CROSS), a generalization of SAR. We show that CROSS, when suitably optimized, correlates strongly with a standard measure of soil permeability reduction for an agricultural soil leached with winery wastewater, and that it can be incorporated directly into existing irrigation water quality guidelines by replacing SAR.
Role of ionic polarization and dielectric decrement in the estimation of surface potential of clay particles. European Journal of Soil Science (2019). Liu, X., Tian, R., Ding, W., Wu, L., & Li, H. https://doi.org/10.1111/ejss.12801
The surface potential of clay particles plays a pivotal role in soil mineral–water interfacial reactions. A new model to estimate surface potential was established taking into account dielectric decrement extracted from the Langevin equation and taking account of ion polarization under a strong electric field. The intensity of ion polarization was quantified through the effective charges of counterions, which are from 1 to 1.036 for Na+ and from 1 to 1.534 for Cs+ at the montmorillonite surface in aqueous solutions. The effective charges were overestimated because the dielectric decrement was disregarded. The surface potential decreases with increasing ion polarizability and dielectric constant. The clay–ion interaction energies were estimated from the effective charges of ions and surface potentials. We observed that the strong additional energies from ion polarization depended on the electron configuration of the counterions at charged surfaces, which not only results from the dispersion interactions, but also the strong induction interactions. The contributions of the latter to the total energy were much stronger than those of the dispersion interactions for Cs+. The strong electric field near the clay surface clearly enhanced the polarizability of Cs+. The energies of non-valence electrons of ions at the charged surfaces were substantially understated in electrolyte solutions. The experimental adhesive forces between silica and mica surfaces in different cation species can be predicted correctly through the surface potential calculated using the new model.
Assessing salinity leaching efficiency in three soils by the HYDRUS-1D and -2D simulations. Ting Yang, Jirka Šimunek, Minghao Mo, Blake Mccullough-Sanden, Hossein Shahrokhnia, Setrag Cherchian, Laosheng Wu*. Soil & Tillage Research (2019). https://doi.org/10.1016/j.still.2019.104342
Salinity leaching is necessary to sustain agricultural production in irrigated croplands. Improving salinity leaching efficiency not only conserves water but also reduces groundwater contamination. Current leaching requirement (LR) calculations are based on steady-state and one-dimensional (1D) approaches, and consequently, this LR concept may not be applicable to drip irrigation (approximately 2D), which is becoming more common due to its higher water use efficiency. The aims of this study were to assess the salinity leaching fraction (LF) in clay, loam, and sand soils under 1D (to mimic sprinkler irrigation) and 2D (to mimic drip irrigation) transient conditions with a numerical model (HYDRUS). Water applications used the actual irrigation scheme in an almond orchard located in central California without considering precipitation. Model simulations showed that soil salinity at the lower boundary (depth of 150 cm) reached steady-state in 10 years in HYDRUS-1D simulations. The leaching fractions calculated from the ratio of drainage-water depth to irrigation-water depth (LFw = Ddw/Diw) and irrigation-water salinity to drainage-water salinity (LFEC = ECiw/ECdw) from HYDRUS-1D were similar among different textured soils. However, they were much higher under drip irrigation (2D) than under sprinkler irrigation (1D) when the same amount of water was applied, and LFEC values were much greater than the LFw values under 2D simulations. Salt balance (SB) and leaching efficiency (LE) indicated that sprinkler irrigation (1D) is more effective for salinity leaching than drip irrigation (2D). To improve salinity leaching efficiency, further evaluation of LRs under drip irrigation is needed.