Riverside, CA, United States
Riverside, CA, United States

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Luo L.,Us Salinity Laboratory | Luo L.,University of California at Riverside | Yates S.R.,Us Salinity Laboratory | Ashworth D.J.,Us Salinity Laboratory
Journal of Environmental Quality | Year: 2011

Due to ever-increasing state and federal regulations, the future use of fumigants is predicted on reducing negative environmental impacts while offering sufficient pest control efficacy. To foster the development of a best management practice, an integrated tool is needed to simultaneously predict fumigant movement and pest control without having to conduct elaborate and costly experiments. The objective of this study was (i) to present a two-dimensional (2-D) mathematical model to describe both fumigant movement and pest control and (ii) to evaluate the model by comparing the simulated and observed results. Both analytical and numerical methods were used to predict methyl iodide (MeI) transport and fate. To predict pest control efficacy, the concentration-time index (CT) was defined and a two-parameter logistic survival model was used. Dose-response curves were experimentally determined for MeI against three types of pests (barnyardgrass [Echinochloa crus-galli] seed, citrus nematode [Tylenchulus semipenetrans], and fungi [Fusarium oxysporum]). Methyl iodide transport and pest control measurements collected from a 2-D experimental system (60 by 60 cm) were used to test the model. Methyl iodide volatilization rates and soil gas-phase concentrations over time were accurately simulated by the model. The mass balance analysis indicates that the fraction of MeI degrading in the soil was underestimated when determined by the appearance of iodide concentration. The experimental results showed that after 24 h of MeI fumigation in the 2-D soil chamber, fungal population was not suppressed; >90% of citrus nematodes were killed; and barnyardgrass seeds within 20-cm distance from the center were affected. These experimental results were consistent with the predicted results. The model accurately estimated the MeI movement and control of various pests and is a powerful tool to evaluate pesticides in terms of their negative environmental impacts and pest control under various environmental conditions and application methods. Copyright © 2011 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Luo L.,Us Salinity Laboratory | Luo L.,University of California at Riverside | Lin H.,Pennsylvania State University | Schmidt J.,University Park
Soil Science Society of America Journal | Year: 2010

Quantitative relationships between soil structure, especially macropore characteristics, and soil hydraulic properties are essential to improving our ability to predict flow and transport in structured soils. The objectives of this study were to quantitatively relate macropore characteristics to saturated hydraulic conductivity (Af) and dispersivity (X) and to identify major macropore characteristics useful for estimating soil hydraulic properties under saturated condition. Large intact soil columns were taken from two land uses (cropland and pasture) of the same soil type (a Typic Hapludalf), with four replicates for each land use. The soil columns were scanned using X-ray computed tomography (CT) to obtain macropore parameters including macroporosity, length density, mean tortuosity, network density, hydraulic radius, path number, node density, and mean angle. The K sar of the whole soil column, as well as each soil horizon within the column, and solute breakthrough curve (BTC) of CaBr 2 were determined for each column. For all eight soil columns studied, macroporosity and path number (the number of independent macropore paths between two boundaries) explained 71 to 75% of the variability in the natural logarithm of K values of the whole soil columns as well as of individual soil horizons. The traditional convection-dispersion equation (equilibrium model) simulated the BTCs well for all soil columns except one with an earthworm hole passing through the entire column, for which the two-region model (non-equilibrium model) was required. The path number, hydraulic radius, and macropore angle were the best predictors for X, explaining 97% of its variability. Correlation between X of the whole soil columns and K sar values of the Bt horizons (but not A horizons) implied that the dispersivity was mainly controlled by the horizon with the lowest K sar in the soil columns. These results indicate that the most useful macropore parameters for predicting flow and transport under saturated condition in structured soils included macroporosity, path number, hydraulic radius, and macropore angle. © Soil Science Society of America, 5585 Guilford Rd. Madison Wl 53711 USA All rights reserved.

Bradford S.A.,Us Salinity Laboratory | Wang Y.,University of California at Riverside | Kim H.,Chonbuk National University | Torkzaban S.,CSIRO | Simunek J.,University of California at Riverside
Journal of Environmental Quality | Year: 2014

An understanding of microbial transport and survival in the subsurface is needed for public health, environmental applications, and industrial processes. Much research has therefore been directed to quantify mechanisms influencing microbial fate, and the results demonstrate a complex coupling among many physical, chemical, and biological factors. Mathematical models can be used to help understand and predict the complexities of microbial transport and survival in the subsurface under given assumptions and conditions. This review highlights existing model formulations that can be used for this purpose. In particular, we discuss models based on the advection-dispersion equation, with terms for kinetic retention to solid-water and/or air-water interfaces; blocking and ripening; release that is dependent on the resident time, diffusion, and transients in solution chemistry, water velocity, and water saturation; and microbial decay (first-order and Weibull) and growth (logistic and Monod) that is dependent on temperature, nutrient concentration, and/or microbial concentration. We highlight a tworegion model to account for microbe migration in the vicinity of a solid phase and use it to simulate the coupled transport and survival of Escherichia coli species under a variety of environmentally relevant scenarios. This review identifies challenges and limitations of models to describe and predict microbial transport and survival. In particular, many model parameters have to be optimized to simulate a diversity of observed transport, retention, and survival behavior at the laboratory scale. Improved theory and models are needed to predict the fate of microorganisms in natural subsurface systems that are highly dynamic and heterogeneous. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Ha W.,Us Salinity Laboratory | Suarez D.L.,Us Salinity Laboratory | Lesch S.M.,University of California at Riverside
Journal of Environmental Quality | Year: 2013

Perchlorate (ClO4 -) has been detected in edible leafy vegetables irrigated with Colorado River water. The primary concern has been the ClO4 - concentration in lettuce (Lactuca sativa L. var. capitata L.). There has been a limited number of studies on ClO4 - uptake, but the interactive effect of other anions on ClO4 - uptake is not known in detail. We conducted a greenhouse ClO4 - uptake experiment using two types of lettuce (iceberg and butterhead) to investigate the interaction of uptake of ClO4 -, Cl-, and NO3 - on ClO4 - uptake under controlled conditions. We examined three concentrations of ClO4 -, 40, 220, and 400 nmolc/L; Cl- at 2.5, 13.75, and 25 mmolc/4L; and NO3 - at 2, 11, and 20 mmolc/L. Perchlorate was taken up the most in lettuce when ClO4 - was the greatest and NO3 - and Cl- were lowest in concentration in the irrigation water. More ClO4 - was detected in leafy material than in root tissue. In general, the outer leaves of iceberg and butterhead lettuce contained more ClO4 - than did the inner leaves. The results indicate that selective ClO4 - uptake occurs for green leaf lettuce. A predictive model was developed to describe the ClO4 - concentration in lettuce as related to the Cl-, NO3 -, and ClO4 - concentration in the irrigation water. Research results can be utilized to elucidate the effect of salts on the accumulation and uptake of ClO4 - by edible leafy vegetables. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Luo L.,Us Salinity Laboratory | Luo L.,University of California at Riverside | Lin H.,Pennsylvania State University | Li S.,Pennsylvania State University
Journal of Hydrology | Year: 2010

The importance of soil macropores as preferential pathways for water, air, and chemical movement in different soils has long been recognized. However, quantification of complex macropore structures and their relationships to soil types and land uses remains elusive. The objectives of this study were to (1) quantify 3-D macropore networks in intact soil columns using an improved approach and (2) investigate the effects of soil type and land use on soil macropore characteristics. Two soils with contrasting textures and structures (Hagerstown silt loam and Morrison sand) from two land uses (row crop and pasture) were investigated. Intact soil columns, 102. mm in diameter and about 350. mm in length, were taken for each soil type-land use combination. The soil columns were scanned using X-ray computed tomography at a voxel resolution of 0.234 mm × 0.234 mm × 2.000 mm. After reconstruction, characteristics of macropore networks were quantified, including continuous macroporosity change along depth, macropore size distribution, network density, surface area, length density, length distribution, mean hydraulic radius, tortuosity, inclination (angle), and connectivity (path number and node density). The approach we developed provided an improved quantification of complex 3-D macropore networks. The analysis of variance indicated that soil type, land use, and their interaction significantly influenced macroporosity, network density, surface area, length density, node density, and mean angle. The interaction of soil type and land use also influenced mean tortuosity and hydraulic radius. Within the same soil type, the soils under pasture land use had greater macroporosity, length density, and node density than that under row crop, especially in the subsoil. This was due to greater organic matter content and more biota activities in the pasture. Within the same land use, the Morrison sand displayed lower overall macroporosity than the Hagerstown silt loam because of weaker structure and higher amount of rock fragments in the Morrison soil and thus less suited for biota activities. The results from this study provide improved quantitative evaluation of a suite of soil macropore features that have significant implications for non-equilibrium flow prediction and chemical transport modeling in field soils. © 2010 Elsevier B.V.

Shouse P.J.,Us Salinity Laboratory | Ayars J.E.,San Joaquin Valley Agricultural Science Center | SimUnek J.,University of California at Riverside
Agricultural Water Management | Year: 2011

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal to deal with this problem is sequential biological concentration (SBC), which is the process of recycling drainage water on increasingly more salt tolerant crops until the volume of drainage water has been reduced sufficiently to enable its final disposal by evaporation in a small area. For maximum effectiveness this concept will require crop water reuse from shallow groundwater. To evaluate the concept of sequential biological concentration, a column lysimeter study was used to determine the potential crop water use from shallow groundwater by alfalfa as a function of ground water quality and depth to ground water. However, lysimeter studies are not practical for characterizing all the possible scenarios for crop water use related to ground water quality and depth. Models are suited to do this type of characterization if they can be validated. To this end, we used the HYDRUS-1D water flow and solute transport simulation model to simulate our experimental results. Considering the precision of the experimental boundary and initial conditions, numerical simulations matched the experimental results very well. The modeling results indicate that it is possible to reduce the dependence on experimental research by extrapolating experimental results obtained in this study to other specific sites where shallow saline groundwater is of concern. © 2011.

Carter C.T.,Tennessee Technological University | Grieve C.M.,Us Salinity Laboratory
HortScience | Year: 2010

Zinnia elegans, because of its economic value and the hardiness of its wild relatives, was selected as a potential salt-tolerant cut flower crop to grow in greenhouse systems using recycled agricultural wastewater. Using recycled wastewater for irrigation of cut flowers provides an alternative to high-quality water. This is especially important in coastal and inland growing regions of California where competition for high-quality water is increasing between urban and agricultural users and provides economic and environmental benefits because groundwater contamination is reduced or even prevented. A completely randomized design was used to determine the effects of water ionic composition and salinity on the growth and leaf mineral composition of Zinnia elegans. Two cultivars (Benary's Giant Salmon Rose and Benary's Giant Golden Yellow) were grown under irrigation with two different water ionic compositions mimicking dilutions of sea water (SWD) and concentrations of Colorado River water (CRW) at increasing salinity levels with electrical conductivities of 2.5 (control), 4.0, 6.0, 8.0, and 10.0 dS-m-1 in greenhouse sand tanks in Riverside, CA. Leaf mineral concentrations were determined for calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), chlorine (Cl), total sulfur (S), and total phosphorus (P). At harvest, final plantmeasurements included time to flowering, stemlength, stem diameter (recorded at the soil line), internode length (recorded at the middle of the stem), inflorescence diameter, ray length, plant shoot fresh weight, number of leaves per plant, and number of shoots per plant. For both cultivars, plant tissue concentrations of Mg, Cl, Na, and total S increased as salinity increased in the irrigation water. Conversely, plant tissue concentrations of Ca, K, and total P decreased as salinity increased in the irrigation water. Both cultivars demonstrated high selectivity for K over Na as salinity increased in CRW and SWD with 'Golden Yellow' demonstrating a higher selectivity than 'Salmon Rose'. Additionally, measured growth parameters tended to decrease as salinity increased in both irrigationwater types for both cultivars. Stemlengths of 79 cm and 51 cmwere found for 'Salmon Rose' growing in 10 dS-m-1 in concentrations of CRWand SWD, respectively. 'Golden Yellow' produced stem lengths of 74 cm and 46 cm in 10 dS-m-1 in response to concentrations of CRW and SWD, respectively. Inflorescence diameters of both cultivars approximated 8.0 cm at the highest salinity for both water types. Although significant differences were found, the minimum of 46 cm indicates that marketable flowers can be produced using both water types at least as high as 10 dS-m-1.

Skaggs T.H.,Us Salinity Laboratory | Suarez D.L.,Us Salinity Laboratory | Goldberg S.,Us Salinity Laboratory
Vadose Zone Journal | Year: 2013

Advanced numerical simulation models can potentially help improve guidelines for irrigation and salinity management. Many simulation model parameters have considerable uncertainty, and ideally that uncertainty should be reflected in model predictions and recommendations. In this work, we investigate solute transport predication intervals that can be generated by propagating model parameter uncertainty using Monte Carlo techniques. Flow and transport is simulated with a standard numerical model, while soil parameters and their uncertainty are estimated with pedotransfer functions. Generalized global sensitivity coefficients are computed to determine the parameters having the greatest impact on transport prediction and uncertainty. Simulations are compared with Br transport measured under unsaturated conditions in large lysimeters packed with clayey soil materials. In a 48 cm tall, homogeneous soil profile, model prediction intervals provided a reasonably good description of a single, relatively "noisy" breakthrough curve. In replicated 180 cm tall, layered soil profiles, model structural errors limited the accuracy of the prediction intervals under one irrigation water treatment, whereas under another treatment the predictions tracked the time course of the data reasonably well but tended to overestimate solute concentrations. The width of the prediction intervals tended to be small relative to the range of transport variability that existed across replicated lysimeters, particularly at shallow depths. Additional work aimed at operational field testing of model prediction uncertainty is needed if advanced water management models are to reach their full potential. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved.

Siyal A.A.,Sindh Agriculture University | Skaggs T.H.,Us Salinity Laboratory | van Genuchten M.T.,Federal University of Rio Grande do Sul
Vadose Zone Journal | Year: 2010

A traditional method of reclaiming salt-affected soils involves ponding water on a field and leaching salts from the soil through a subsurface tile drainage system. Because water and salts move more slowly in areas midway between drain lines than in areas near the drains, achieving a desired level of desalinization across the entire field requires that ponding continue long after areas close to the drains are already free of salts, thus causing an inefficient leaching process that wastes water. A partial ponding method of leaching was recently suggested to improve the leaching efficiency by up to 85%. In this study, we tested the partial ponding method for its potential to save water and time by simulating the leaching of salts from salt-affected profiles with various soil textures, tile-drain depths, and soil depths. Simulations for laboratory sand tanks and field conditions both showed that transport velocities midway between drains are greater under partial ponding than under total ponding because the local hydraulic head gradient is larger under partial ponding conditions. As the ponded area increases toward the drain, water originating from areas near the drain moves faster than water from midway between the drains. By adopting partial ponding, water and time savings of 95 and 91%, respectively, were found possible for a sandy soil. The method also showed water savings of 84% when applied to a loam soil and 99% for a layered sand over loam soil but only 13% when applied to a layered loam over sand soil. © Soil Science Society of America.

Suarez D.L.,Us Salinity Laboratory | Wood J.D.,Us Salinity Laboratory | Taber P.E.,Us Salinity Laboratory
Vadose Zone Journal | Year: 2012

Reuse of agricultural drainage waters, treated municipal wastewaters, and brackish groundwaters is often impaired by elevated concentrations of B. Boron is an element with a narrow concentration range between deficiency and toxicity for plants. Knowledge of the B concentrations in soil solution and transport of B out of the root zone is essential for management of wastewaters. Prediction of B concentrations in the root zone requires consideration of soil adsorption and desorption of B, which are dependent on soil properties and solution composition, especially pH. We examine B transport in soil by first applying a 0.08-mmol L_1 B solution to three arid-land soils from southern California and subsequently leaching the soils with a low B solution. The experiment was conducted with irrigation water at pH 6.0 and 9.0. The data showed that transport was highly pH dependent. Results from the column experiments were generally well predicted using the UNSATCHEM transport model with the B subroutine that includes the constant capacitance model and prediction of the model constants for each soil based on the specific soil properties. Use of a single set of average constants for all soils in combination with a calculated surface area provided a less satisfactory fit to the experimental data, especially at elevated pH. These results indicate that B transport can be predicted without the need for time-consuming and soil-specific determinations of B adsorption characteristics if we utilize predictive relations to predict the CCM constants from individual soil properties. © Soil Science Society of America.

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