California Soils Research Articles

Multi-Sensor Soil Probe and Machine Learning Modeling for Predicting Soil Properties

We present a data-driven, in situ proximal multi-sensor digital soil mapping approach to develop digital twins for multiple agricultural fields. A novel Digital Soil CoreTM (DSC) Probe was engineered that contains seven sensors, each of a distinct modality, including sleeve friction, tip force, dielectric permittivity, electrical resistivity, soil imagery, acoustics, and visible and near-infrared spectroscopy. The DSC System integrates the DSC Probe, DSC software (v2023.10), and deployment equipment components to sense soil characteristics at a high vertical spatial resolution (mm scale) along in situ soil profiles up to a depth of 120 cm in about 60 s. The DSC Probe in situ proximal data are harmonized into a data cube providing vertical high-density knowledge associated with physical–chemical–biological soil conditions. In contrast, conventional ex situ soil samples derived from soil cores, soil pits, or surface samples analyzed using laboratory and other methods are bound by a substantially coarser spatial resolution and multiple compounding errors. Our objective was to investigate the effects of the mismatched scale between high-resolution in situ proximal sensor data and coarser-resolution ex situ soil laboratory measurements to develop soil prediction models. Our study was conducted in central California soil in almond orchards. We collected DSC sensor data and spatially co-located soil cores that were sliced into narrow layers for laboratory-based soil measurements. Partial Least Squares Regression (PLSR) cross-validation was used to compare the results of testing four data integration methods. Method A reduced the high-resolution sensor data to discrete values paired with layer-based soil laboratory measurements. Method B used stochastic distributions of sensor data paired with layer-based soil laboratory measurements. Method C allocated the same soil analytical data to each one of the high-resolution multi-sensor data within a soil layer. Method D linked the high-density multi-sensor soil data directly to crop responses (crop performance and behavior metrics), bypassing costly laboratory soil analysis. Overall, the soil models derived from Method C outperformed Methods A and B. Soil predictions derived using Method D were the most cost-effective for directly assessing soil–crop relationships, making this method well suited for industrial-scale precision agriculture applications.

Adsorption of imazamox in California agricultural soils and implications for branched broomrape (Phelipanche ramosa) management

Results of previous research on chemigated imazamox for control of branched broomrape (Phelipanche ramosa) in processing tomatoes suggested potential soil-type differences in imazamox availability. Over two years, there were differences in crop-injury between two sites less than 30-km apart: imazamox-treated tomatoes in the Davis location had relatively minor early season injury while tomatoes at the Woodland location were severely injured or killed. The following study was conducted to investigate imazamox sorption in four California soils to determine if differences in herbicide adsorption played a role in variable crop-injury observed in the field trials. To determine the sorption capacity of imazamox of each soil, a batch-equilibrium study was conducted. There were significant differences in sorbed imazamox: the clay soil had the highest adsorption (Robert’s Island: 742.5 pg µL−1 sorbed), followed by the sandy loam soil (Ripon: 723.9 pg µL−1 sorbed), while the loam soils from both trial sites (Davis: 704.2 pg µL−1 sorbed; Woodland: 699.9 pg µL−1 sorbed) had the lowest adsorption and were not significantly different from one another. Results from this study illustrate only minor differences in imazamox adsorption among the soils tested which suggests that soil type was likely not a major factor contributing to differences in crop-injury.

Two novel heat-tolerant, culturable rhizosphere-inhabiting, plant growth-promoting ascomycete fungi associated with native plants in desert habitats of southwestern USA

During an investigations on Monosporascus cannonballus, the causal agent of root rot and vine decline of melons, in 1999, a previously unknown rhizosphere fungus was encountered in the desert soils of southern California. The fungus, herein named Desertella arida Stanghellini & Mohammadi sp. nov., was associated with roots of diverse plants including brassica (Sahara mustard (Brassica tournefortii), shepherd's purse (Capsella bursa-pastoris)) and plantain (Plantago ovata Forsk). The fungus forms extensive multinucleate, septate hyphae (6–17 μm in diameter) bearing hundreds of large spherical to pear-shaped unicellular asexual spores (50–120 μm in diameter), either singly or in large clusters. The spores are beige to cream-colored, thin-walled, and contain a dense, granular cytoplasm. Further investigation on the distribution of D. arida in soils of desert habitats in the southwestern USA led to the discovery of a second fungus belonging to a different species herein named Desertella americanense Mohammadi & Stanghellini sp. nov., in California, Arizona, Nevada, and Utah. The two species are morphologically similar. Spores from both fungi in native soil survived heat treatment up to 100 °C. Both species are culturable and colonized roots of monocots and dicots forming abundant hyphae and spores as early as 10 days post-inoculation. Desertella arida significantly enhanced shoot growth in broccoli, lettuce, Plantago ovata and flax. In conclusion, we discovered two desert-dwelling ascomycete fungi that were associated with the roots of native plant species in southern California. They were culturable on a synthetic medium, heat-tolerant and promoted growth on several crop species. These fungi appeared to exist in other neighboring states such as Arizona and Nevada.

Effects of tire wear particles on the water retention of soils with different textures in the full moisture range

Tire wear particles (TWPs) are significant contributors to microplastic pollution in the environment, yet there is limited scientific information concerning their impact on soil hydraulic properties. This study aimed to investigate the impact of TWPs at different concentrations (1, 4, 8, and 16% of the air-dried mass of packed soil samples, w/w) on the water retention curves (WRC) of southern California soils with five different textures (clay, clay loam, silt loam, sandy loam, and loamy sand). The concentrations of 8% and 16% were selected to represent extreme pollution scenarios that might occur near highway corridors. High-resolution water retention data, spanning from saturation to oven dryness, were generated using HYPROP™ and WP4C dew point meter instruments. We also developed WRC scaling equations based on the quantity of TWPs. The bulk density of the samples decreased as the TWP concentration in soils increased. The inclusion of very high concentrations of TWPs (8% and 16% w/w) led to a significant reduction in soil moisture content in the intermediate and dry ranges across various soil textures. However, at the same moisture range, adding 1% TWPs had a minimal impact on soil moisture reduction, while the influence of the 4% TWPs concentration treatment was noticeable only in loamy sand and partially in clay loam soils. Additionally, the overall plant available water decreased with increasing TWP concentrations, except for the clay soil. The texture-specific scaling models exhibited promising performance, with RMSE values ranging from 0.0061 to 0.0120 cm3 cm−3. When bulk density was included as an additional input predictor to construct a single scaling model for all textures, the RMSE increased. Nevertheless, it still indicated a good fit ranging from 0.007 to 0.024 cm3 cm−3, highlighting the suitability of simple scaling for identifying WRC in TWPs-polluted soils, particularly for practical purposes. The findings of this study can contribute to a better understanding and quantification of the impact of TWPs on soil hydrology.

Can saturated paste be used to predict bulk density in annual cropping systems in California?

AbstractSoil bulk density (BD) is important for measuring changes in soil chemical, physical, and biological properties; however, the measurement is tedious to collect and requires specialized equipment. Database measurements for soil surface BD do not always correspond to present field conditions as field management can alter BD in time. Saturation percentage (SP) is a routine lab measurement. The objectives of this study are to (1) understand if a relationship between BD and SP can be developed and (2) build a model that predicts BD based on a routine low‐cost lab analysis. We collected 83 soil samples from different experimental sites around California's Central Valley. At each site, BD, SP, soil organic matter (OM), and soil total organic carbon were measured. A set of models were generated and compared based on their Akaike information criterion (AIC) and adjusted R2. The best two models are presented in this paper, and their accuracy and precision in estimating BD were further compared by calculating the root mean square error (RMSE) and the R2 of the predicted versus values measured in the field. We determined that a strong relationship between BD and SP exists (R2 = 0.70) and that a cubic model that includes SP and OM resulted in the best model to predict BD in California soils. Inclusion of additional data may further strengthen this model or make it applicable for other grower regions.

Identification and characterization of Entyloma eschscholziae, a recently introduced pathogen in Europe, and its segregate Entyloma dendromeconis sp. nov.

AbstractEntyloma includes pathogenic and saprobic species that infect or colonize dicotyledonous host plants. Although most Entyloma species are known only from native areas of occurrence, some species were introduced with their host plants and spread outside their natural areas. The identification of introduced species is important for detection and management of invasive species. In this study, the morphology, phylogeny and species boundaries of Entyloma eschscholziae, recently introduced from North America to Europe, are revisited. Morphology was similar among the type and other specimens of E. eschscholziae analysed on Eschscholzia californica. Both asexual and sexual morphs were observed. The rDNA ITS1‐5.8S‐ITS2 sequences of the E. eschscholziae specimens from Europe and New Zealand and the environmental sequence obtained from grassland soil in California, United States, were identical. Morphological and molecular analyses confirm that the causative agents of white smut on E. californica in native (North America) and introduced (Europe, New Zealand) areas belong to the same species. DNA barcodes obtained in this study (especially ITS sequence from the designated epitype specimen) could be used to facilitate its molecular identification. Specimens on Dendromecon rigida, previously assigned to E. eschscholziae, are morphologically distinct. An attempt to obtain DNA barcode data from degraded holotype material was not successful and no more recent material is available. However, based on the morphological differences and high host specificity found in Entyloma spp., it is appropriate to describe a new species, Entyloma dendromeconis, for this smut pathogen.

Assessing Weathering, Pedogenesis, and Silt Generation in Granitoid‐Hosted Soils From Contrasting Hydroclimates

AbstractThe origin and production of silt are key factors in the formation of loess deposits. Although many processes can potentially lead to silt generation, few are known to produce silt in the volumes and particle‐size modes required to form geologically significant loess deposits. Here, we investigate the hypothesis that soil‐associated weathering in tropical and Mediterranean climates can generate abundant in situ silt, and therefore contribute significantly to loess formation throughout geologic time. We utilize granulometric and geochemical data from two granitoid‐hosted soils formed in Puerto Rico (hot‐humid climate) and Southern California (hot‐arid climate) to discern whether the silt + clay fraction (<62.5 μm) is generated from bedrock weathering (autochthonous) or sourced from eolian contributions (allochthonous). Our study demonstrates that the PR soil contains abundant (up to 72%) silt‐ and clay‐sized particles compared to the Southern California soil (<6%). However, the silt fraction of the PR soil is at least partially derived from eolian inputs, and the silt fraction of the Southern California soil is geochemically indistinguishable from allochthonous dust sources. Furthermore, while intense chemical weathering in PR can produce abundant fines, the majority are significantly finer (average mode ∼15 μm) than the modes of most “typical” loess deposits (modes more than 20–30 μm). In contrast, weathering in the Southern California soil produces volumetrically sparse silt. Hence, weathering processes within these two profiles, representing hot‐humid and hot‐dry climates, appear to be ineffectual for producing the volume and size distributions of silt needed to generate significant loess deposits.

Guayule as an alternative crop for natural rubber production grown in B- and Se-laden soil in Central California

The potential of growing guayule ( Parthenium argentatum A. Gray) as an alternative crop for saline, boron- and selenium-laden soils in the Westside of central California was evaluated in both greenhouse and drainage sediment field experiments. In the greenhouse experiment, salt and boron (B) tolerance and selenium (Se) accumulation were evaluated in guayule accessions AZ-1 thru AZ-6 grown in saline soil and irrigated with simulated saline drainage water. The guayule accessions AZ1, AZ5, and AZ6 tolerated salinity and B levels better than the others. Consequently, AZ1, AZ5, and AZ6 were then planted in field sediment plots with slight salinity and moderate B levels. In both greenhouse and field studies, concentrations of Se, B, and Na in the leaves were as high as 0.6–8 mg/kg dry weight (DW), 2000 mg/kg DW, and 17,500 mg/kg DW, respectively, in both experiments. In both experiments, concentrations of rubber and resin ranged from 4 to 14 w/w% in the stems, and applied salinity increased rubber and resin production in some accessions. This two-phase study provides additional evidence for guayule accessions (AZ1–6) as a promising rubber-producing crop that tolerates saline irrigation water in poor quality soils. In addition, guayule may be useful in the gentle phytoremediation of Se in poor quality soils or in soils irrigated with Se-laden drainage water. • Guayule AZ accessions grown under saline, B- and S- laden conditions were evaluated. • Guayule’s tolerance to salinity, B, and Se in soil and irrigation varies by accession. • Boron, Se, and Na accumulation mostly takes place in leaf tissue. • Natural rubber and resin were not negatively affected by slight to moderate salinity. • Accession AZ5 was best suited for salinity and B.

Random forest analysis reveals taxa predictive of Prunus replant disease in peach root microbiomes

Successive plantings of Prunus species produce suboptimal growth and yield in many California soils due to a poorly understood soilborne disease complex, Prunus replant disease (PRD). We explored the hypothesis that PRD is mediated by microbial taxa in roots of Nemaguard peach, a rootstock for almond and other stone fruits. In a greenhouse bioassay, portions of 10 replant soils were treated with fumigation or pasteurization or left untreated as a control before being planted with peach seedlings. Ten weeks after planting, seedlings were considered PRD-affected if their top fresh weights in the control were significantly reduced, compared to the weights in pasteurization and fumigation treatments; plants with equivalent top weights in all treatments were considered to be non-affected. The roots were washed from the soil, frozen, extracted for total DNA, and used for metabarcoding of rRNA gene amplicons from bacteria, fungi, and oomycetes. High-throughput amplicon sequencing revealed that root microbial community shifts resulted from preplant treatments, and specific taxa were associated with PRD induction among controls. Random forest (RF) analysis discriminated effectively between PRD-affected and non-affected root communities. Among the 30 RF top-ranked amplicon sequence variant (ASV) predictors, 26 were bacteria, two were oomycetes, and two were fungi. Among them, only Streptomyces scabiei, Steroidobacter denitrificans, Streptomyces bobili, and Pythium mamillatum had root abundances ≥5% that were either associated positively (former two ASVs) or negatively (latter two) with PRD. Thus, our findings were consistent with microbial mediation of PRD in roots and suggested taxa that may be involved in the mediation.

Characterization of soils conducive and non-conducive to Prunus replant disease.

Successive orchard plantings of almond and other Prunus species exhibit reduced growth and yield in many California soils. This phenomenon, known as Prunus replant disease (PRD), can be prevented by preplant soil fumigation or anaerobic soil disinfestation, but its etiology is poorly understood and its incidence and severity are hard to predict. We report here on relationships among physicochemical variables, microbial community structure, and PRD induction in 25 diverse replant soils from California. In a greenhouse bioassay, soil was considered to be “PRD-inducing” when growth of peach seedlings in it was significantly increased by preplant fumigation and pasteurization, compared to an untreated control. PRD was induced in 18 of the 25 soils, and PRD severity correlated positively with soil exchangeable-K, pH, %clay, total %N, and electrical conductivity. The structure of bacterial, fungal, and oomycete communities differed significantly between the PRD-inducing and non-inducing soils, based on PERMANOVA of Bray Curtis dissimilarities. Bacterial class MB-A2-108 of phylum Actinobacteria had high relative abundances among PRD-inducing soils, while Bacteroidia were relatively abundant among non-inducing soils. Among fungi, many ASVs classified only to kingdom level were relatively abundant among PRD-inducing soils whereas ASVs of Trichoderma were relatively abundant among non-inducing soils. Random forest classification effectively discriminated between PRD-inducing and non-inducing soils, revealing many bacterial ASVs with high explanatory values. Random forest regression effectively accounted for PRD severity, with soil exchangeable-K and pH having high predictive value. Our work revealed several biotic and abiotic variables worthy of further examination in PRD etiology.

Forecasts of Opportunity for Northern California Soil Moisture

Soil moisture anomalies underpin a number of critical hydrological phenomena with socioeconomic consequences, yet systematic studies of soil moisture predictability are limited. Here, we use a data-adaptive technique, Linear Inverse Modeling, which has proved useful as an indication of predictability in other fields, to investigate the predictability of soil moisture in northern California. This approach yields a model of soil moisture at 10 stations in the region, with results that indicate the possibility of skillful forecasts at each for lead times of 1–2 weeks. An important advantage of this model is the a priori identification of forecasts of opportunity—conditions under which the model’s forecasts may be expected to have particularly high skill. Given that forecast errors (and inversely, their skill) can be estimated in advance, these findings have the potential to greatly increase the utility of soil moisture forecasts for practical applications including drought and flood forecasting.

Rock-Sourced Nitrogen in Semi-Arid, Shale-Derived California Soils

Models suggest that rock-derived nitrogen (N) inputs are of global importance to ecosystem N budgets; however, field studies demonstrating the significance of rock N inputs are rare. We examined rock-derived N fluxes in soils derived from sedimentary rocks along a catena formed under a semi-arid climate. Our measurements demonstrate that there are distinct and traceable pools of N in the soil and bedrock and that the fraction of rock-derived N declines downslope along the catena. We used geochemical mass balance weathering flux measurements to estimate a rock-derived N flux of 0.145 to 0.896 kg ha–1 yr–1 at the ridgecrest. We also developed independent N flux estimates using a 15N-based isotope mixing model. While geochemical mass-balance-based estimates fell within the 95% confidence range derived from the isotope mixing model (−1.1 to 44.3 kg ha–1 yr–1), this range was large due to uncertainty in values for atmospheric 15N deposition. Along the catena, N isotopes suggest a diminishing effect of rock-derived N downslope. Overall, we found that despite relatively large N pools within the saprolite and bedrock, slow chemical weathering and landscape denudation limit the influence of rock-derived N, letting atmospheric N deposition (7.1 kg ha–1 yr–1) and N fixation (0.9–3.1 kg ha–1 yr–1) dominate N inputs to this grassland ecosystem.

Growth Characteristics and Infiltration Rate in Kentucky Bluegrass, Perennial Ryegrass and Tall Fescue Grown under California Soil System in Soccer Field

Growth Characteristics and Infiltration Rate in Kentucky Bluegrass, Perennial Ryegrass and Tall Fescue Grown under California Soil System in Soccer Field

Assessment of Nitrogen Oxide Emissions and San Joaquin Valley PM2.5 Impacts From Soils in California

AbstractSoils are a source of atmospheric nitrogen oxides (NOx), especially in regions with significant cropland where nitrogen (N) fertilizers are used to enhance crop yields. The magnitude of soil NOx emissions, however, varies substantially by region, depending on the local land use pattern and management activities. We estimated soil NOx emissions in California based on the DeNitrification‐DeComposition (DNDC) biogeochemical model, linked to a detailed spatial‐temporal differentiated California‐specific database. The DNDC‐generated surface fluxes were used in the Community Multiscale Air Quality (CMAQ) model to evaluate impacts of soil NOx emissions on formation of ambient particulate (PM2.5) nitrate in the San Joaquin Valley (SJV) where cropland is the dominant land use. The DNDC‐generated soil NOx emissions contribute approximately 1.1% of total anthropogenic NOx emissions in California, at an emission rate of roughly 24 t day−1 (as NO2) statewide and 9 t day−1 in the SJV. Cropland is the dominant source of soil NOx emissions in California, contributing nearly 60% of statewide soil NOx emissions, driven principally by fertilizer use. The PM2.5 nitrate concentrations simulated by CMAQ using the DNDC‐generated soil NOx emissions are compatible with those observed in the SJV, suggesting that soil NOx emissions have limited impacts on PM2.5 nitrate formation in the atmosphere. Our emission and air quality modeling results are further supported by long‐term ambient NOx‐to‐carbon monoxide (CO) and satellite NO2 data analyses in the SJV, which showed diurnal, monthly, and annual trends consistent with characteristics of NOx sources dominated by traffic combustion in both urban and agricultural regions.

Genome Sequences of Bacteriophages ClearAsMud and Kauala, Isolated from Microbacterium foliorum

Cluster EC ClearAsMud and cluster EA4 Kauala are lytic Siphoviridae bacteriophages that were isolated from soil in southern California using Microbacterium foliorum NRRL B-24224 as the host. The ClearAsMud and Kauala genomes are 52,987 bp and 39,378 bp, respectively, and contain 92 and 56 predicted protein-coding genes, respectively.

Accumulation and speciation of selenium in biofortified vegetables grown under high boron and saline field conditions

Selenium (Se) biofortification, as an agronomic-based strategy, is utilized to produce Se-enriched food products for increasing Se intake in inhabitants in Se-deficient regions. This strategy can be accomplished by soil and foliar application of Se or by growing crops in soils naturally high in Se. In this study, different cruciferous vegetables were field-grown in high boron (B) and saline soils of central California containing naturally high levels of Se. We investigated whether Se biofortification occurs in salt- and B-tolerant vegetables grown in poor-quality soil. The uptake of Se and other elements occurred in all vegetables. In plant tissues, Se speciation analyses showed greatest percentages of Se-containing compounds were contained in organic Se forms (monomethylated) and as selenate in the inorganic Se forms. Selenium-enriched vegetables produced from saline soils high in B and Se can be a natural source of Se-biofortified food that can be consumed as bioactive food products.

Evaluating uncertainty in Landsat-derived postfire recovery metrics due to terrain, soil, and shrub type variations in southern California

ABSTRACT Temporal trajectories of apparent vegetation abundance based on the multi-decadal Landsat image series provide valuable information on the postfire recovery of chaparral shrublands, which tend to mature within one decade. Signals of change in fractional shrub cover (FSC) extracted from time-sequential Normalized Difference Vegetation Index (NDVI) data can be systematically biased due to spatial variation in shrub type, soil substrate, or illumination differences associated with topography. We evaluate the effects of these variables in Landsat-derived metrics of FSC and postfire recovery, based upon three chaparral sites in southern California which contain shrub community ecotones, complex terrain, and soil variations. Detailed validations of prefire and postfire FSC are based on high spatial resolution ortho-imagery; cross-stratified random sampling is used for variable control. We find that differences in the composition and structure of shrubs (inferred from ortho-imagery) can substantially influence FSC-NDVI relations and impact recovery metrics. Differences in soil type have a moderate effect on the FSC-NDVI relation in one of the study sites, while no substantial effects were observed due to variation of terrain illumination among the study sites. Arithmetic difference recovery metrics – based on NDVI values that were not normalized with unburned control plots – correlate in a moderate but significant manner with a change in FSC (R 2 values range 0.47–0.59 at two sites). Similar regression coefficients resulted from using Landsat visible reflectance data alone. The lowest correlations to FSC resulted from Soil-Adjusted Vegetation Index (SAVI) and are attributed to the effects of the soil-adjustment factor in sparsely vegetated areas. The Normalized Burn Ratio and Normalized Burn Ratio 2 showed a moderate correlation to FSC. This study confirms the utility of Landsat NDVI data for postfire recovery evaluation and implies a need for stratified analysis of postfire recovery in some chaparral landscapes.

Soil Management Practices to Mitigate Nitrous Oxide Emissions and Inform Emission Factors in Arid Irrigated Specialty Crop Systems

Greenhouse gas (GHG) emissions from arid irrigated agricultural soil in California have been predicted to represent 8% of the state’s total GHG emissions. Although specialty crops compose the majority of the state’s crops in both economic value and land area, the portion of GHG emissions contributed by them is still highly uncertain. Current and emerging soil management practices affect the mitigation of those emissions. Herein, we review the scientific literature on the impact of soil management practices in California specialty crop systems on GHG nitrous oxide emissions. As such studies from most major specialty crop systems in California are limited, we focus on two annual and two perennial crops with the most data from the state: tomato, lettuce, wine grapes and almond. Nitrous oxide emission factors were developed and compared to Intergovernmental Panel on Climate Change (IPCC) emission factors, and state-wide emissions for these four crops were calculated for specific soil management practices. Dependent on crop systems and specific management practices, the emission factors developed in this study were either higher, lower or comparable to IPCC emission factors. Uncertainties caused by low gas sampling frequency in these studies were identified and discussed. These uncertainties can be remediated by robust and standardized estimates of nitrous oxide emissions from changes in soil management practices in California specialty crop systems. Promising practices to reduce nitrous oxide emissions and meet crop production goals, pertinent gaps in knowledge on this topic and limitations of this approach are discussed.

Draft Genome Sequence of Massilia sp. Strain MC02, Isolated from a Sandy Loam Maize Soil.

From farmed corn soil in California, we isolated and sequenced a new member of the genus Massilia, Massilia sp. strain MC02. Massilia sp. MC02 has an assembled draft genome of 5,023,356 bp with a total of 4,790 protein-encoding genes and 3,028 predicted proteins, 47 tRNA genes, and 2 rRNA operons.

Lead Absorption by Radish Is Affected by Soil Texture and Cultivar

Lead (Pb) was detected in potential urban garden soil in Claremont Cali-fornia and was absorbed by radish cultivars and giant red mustard in a bioassay of the contaminated soil. Radish cultivars grown in two soils with two lead salts developed the same lead tissue concentrations. In a subsequent study, Cultivar “Rudolf” accumulated less lead nitrate than cultivars “French Breakfast” and “White Beauty”. Cultivar “Rudolf” grew the least biomass likely accounting for its reduced Pb accumulation. All radish cultivars accumulated more lead when grown in clay vs. sand soil and radish Pb accumulation increased when the concentration of lead was increased in either soil type. The solubility of the lead ion used was not associated with Pb uptake by radish.