Preliminary evaluation of H2SO4 application methods to soils

Summary The effects of sulfuric acid application to soils and water on growth and chemical composition of sorghum (Sorghum bicolor) were compared in a greenhouse experiment using high sodium bicarbonate irrigation water. Significant increases in dry matter yield and plant uptake of P en Fe were produced only by soil treatment of calcareous soils.Contribution from the Department of Soils, Water and Engineering, The University of Arizona, Tucson, Arizona 85721, as Technical Paper No. 2320. This work was supported by the Arizona Mining Association.Research assistants and Professor     

Phosphorus availability indices in calcareous lebanese soils

Summary Three indices of available P were evaluated with 20 mainly calcareous Lebanese soils using wheat (Triticum aestivum L.) and tomato (Lycopersicum esculentum L.) in the greenhouse. Both the NaHCO₃-and anion exchange resin-extractable P were significantly correlated with P uptake. The relationship for NaOH–Na₂C₂O₄ was not significant. Langmuir isotherm and actual sorption parameters were also poorly related to uptake. In general, soil properties were not significantly related to extractable P or crop uptake. Sequential inclusion of selected soil properties with test values only slightly improved the multiple correlation coefficients.Contribution from the Department of Soils, Irrigation and Mechanization, American University of Beirut, Beirut, Lebanon. Journal No. 523B. Sci. Paper Series No.297.     

Effect of sulfuric acid on sodium-hazard of irrigation water

Summary The sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP) and saturated hydraulic conductivity were measured under laboratory conditions in one neutral and four calcareous soils using simulated alkaline irrigation waters having salt concentrations ranging from 7 to 39 meq/l with the SAR from 3.8 to 8.4. Sulfuric acid was applied to the waters at sufficient rates to prevent calcium precipitation under an open system, ranging from 2.1 to 4.7 meq/l. At these acid rates, the pH of irrigation waters remained above neutral. This treatment reduced SAR and ESP in all cases tested, and increased the hydraulic conductivity of some soils when the SAR of the original irrigation waters was greater than approximately 7. The experimentally determined SAR was then compared with the values predicted based on some of the existing theories. The results indicated that the conventional method to estimate SAR with adjustment using the pH_C index of Langelier overestimates the effect of HCO₃ ^-, whereas the equation based on carbonate equibria gives a reasonable prediction of SAR in waters containing HCO₃ ^- as well as H₂SO₄. The SAR calculated by the latter method was also linearly related to the measured ESP with an equation, ESP=0.761 SAR, r²=0.986.Arizona Agr. Exp. Sta. J. No. 2449. Contribution from the Department of Soils, Water and Engineering. The University of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Association.Arizona Agr. Exp. Sta. J. No. 2449. Contribution from the Department of Soils, Water and Engineering. The University of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Association.     

Sulfuric acid and leaching requirements for reclaiming sodium-affected calcareous soils

Summary The changes in exchangeable sodium and total dissolved salts due to the application of sulfuric acid and water to sodium-affected calcareous soils were studied for the purpose of establishing a convenient way of determining acid and leaching water requirements. Conventional methods which ignore the effect of sodium removed from soil exchange sites are inadequate for estimating amounts of acid needed to obtain a desired level of exchangeable sodium, especially at high acid application rates. Modified equations are presented which predict the changes in exchangeable sodium and total dissolved salts using essentially the same input data needed for conventional methods, and appear advantageous for estimating acid and leaching water needs. Contribution from the Department of Soils, Water and Engineering, The University of Arizona, Tucson 82751, Arizona Agricultural Experiment Station Journal No. 2340. Supported in part by a grant from the Arizona Mining Association.     

Effect of high boron application on boron content and growth of melons

Synthetic chelates, such as ethylene diamine tetraacetic acid (EDTA), have been shown to enhance phytoextraction of Pb from contaminated soil but also cause leaching of heavy metal-chelate complexes, posing a groundwater contamination threat. In a soil column study, we examined the effect of EDTA and a biodegradable chelate [S,S] isomere of ethylene diamine disuccinate ([S,S]-EDDS), newly introduced in phytoextraction research, on the uptake of Pb by the Chinese cabbage (Brassica rapa) and Pb leaching through the soil profile. Soil water sorption characteristics were modified by acrylamide hydrogel. The addition of 0.1 and 0.2% (w/w) of hydrogel amendments increased soil field water capacity from initial 24.6% to 28.5% and 31.3%, respectively. The additions of 2.5, 5 and 10 mmol EDTA kg^–1 soil were more effective in enhancing Pb plant uptake than comparable [S,S]-EDDS treatments, but caused (as also 10 mmol kg^–1 [S,S]-EDDS additions) unacceptably high Pb leaching in treatments with any soil water sorption conditions tested. The most efficient level of EDTA (10 mmol kg^–1) enhanced plant Pb uptake by 97 times compared to the control. Shoots Pb concentrations reached 500 mg kg^–1 of dry biomass. However, in this treatment 36.2% of total initial Pb was leached from the soil during the first four weeks after chelate addition. Hydrogel soil amendments were more effective in treatments with [S,S]-EDDS than with EDTA. In treatments with 10 mmol kg^–1[S,S]-EDDS hydrogel amended soils, plant Pb uptake was significantly reduced and Pb leach was as high as 44.2% of total initial soil Pb. At lower [S,S]-EDDS concentrations, the effect of hydrogel soil amendment on Pb leaching was the opposite. The addition of 5 mmol kg^–1 [S,S]-EDDS soil to the soil amended with 0.2% hydrogel increased Pb uptake by 18 times while only 0.2% of total initial Pb was leached. In all treatments, the concentrations of Pb in dry plant biomass were far from concentrations required for efficient soil remediation within a reasonable time span.     

Light and assimilation number in a small desert,recharged-groundwater pond

Summary Measurements of irradiance, chlorophyll a concentration, respiration, and net and gross photosynthesis were carried out in a small desert pond containing recharged-groundwater from the Flushing Meadows water reclamation project at Phoenix, Arizona. Over the 6-month period May–October, chl. a concentration averaged 119 mg m^-3; and gross primary productivity in terms of the mean daily carbon fixation rate was 8.29 g C m^-3, which is roughly equal to productive fish and farm ponds but less than many polluted eutrophic lakes and streams. Both net and gross assimilation numbers were found to be satisfactorily represented by pure sine waves that implied total inhibition of those two processes near an underwater irradiance value of 0.32 cal cm^-2 min^-1.The maximum value of the gross assimilation number at 0.16 cal cm^-2 min^-1 of 30 mg C hr^-1 per mg chl. a ranked with some of the highest values that have been found world-wide.Joint contribution of the Department of Zoology, Arizona State University, and the Agricultural Research Service, U.S. Department of Agriculture. Portions of this work were supported by the Grace Ellis Ford Fellowship, American Association of University Women, awarded to Joyce M. Foster on July 1, 1971.     

Relationship among irrigation-media regimes and plant growth

Summary Factors limiting growth in media culture are oxygen, nutrients and water. These factors are dependent on particle diameter, nutrient solution composition, and irrigation frequency. This study evaluated combinations of trickle irrigation frequencies and particle sizes of media on the growth ofChrysanthemum morifolium Ramat. irrigated with a complete nutrient solution. Plant height, fresh weight, dry weight, and flower diameter were used to measure growth. Media used were: coarse incinerated anthracite refuse, fine incinerated anthracite refuse, and soil material from the B21 horizon of Gatesburg sand. Irrigation frequencies were: once per day, four times per day at 4-h. intervals, and constantly during the 13 daylight hours. Fine incinerated anthracite refuse irrigated constantly and every 4 hours produced chrysanthemums with significantly greater height, fresh weight and flower diameter than other treatments, whereas Gatesburg sand irrigated daily resulted in less growth than other treatments. Excess water held in finer textured media causes oxygen deficiency and substandard growth. Authorized for publication November 5, 1973 as paper no.4561 of the Journal series of the Pennsylvania Agr. Exp. Sta., University Park, Pa. 16802. The authors gratefully acknowledge support from The United States Agency for International Development (U.S.A.I.D.), through a 211 (d) grant to the Agronomy Department at The Pennsylvania State University. The information and conclusions in this paper do not necessarily reflect the position of AID or the U.S. Government. Research Assistant, Associate Professor of Floriculture, Associate Professor of Soil Genesis and Morphology, and Associate Professor of International Agronomy, respectively.     

Naproxen Adsorption-Desorption in a Sandy Aquifer Matrix: Characterisation of Hysteretic Behavior at Two Different Temperature Values

Adsorption/desorption processes (sorption isotherms) of Naproxen in a sandy aquifer matrix sediment were investigated using batch tests to compare Naproxen sorption behavior at 15°C and 25°C. Both temperatures are representative of the aquifer media and environmental conditions. Adsorption was well described by linear isotherms with low sorption affinity to aquifer material (K_d of 0.4 μg kg^?1) at both temperatures (15°C and 25°C). Desorption isotherm coefficients at 15°C and 25°C were 5.0 and 4.9, respectively. Naproxen hysteresis indices were between 9.98 and 10.8, indicating that a Naproxen fraction may be irreversibly fixed in the aquifer media, being higher at 25°C (10.88) compared to 15°C, showing a decreasing trend with increasing compound concentration at 15°C. The low sorption of Naproxen leads to potential leaching to groundwater if present in irrigation water, and its prevalence in an aquifer media when directly injected in wells for groundwater recharge.     

Effect of pH on nitrogen immobilization in two California soils

Summary The effect of pH on nitrogen immobilization from tagged NH₄Cl and KNO₃ was investigated in two soils. Although the ammonium source was utilized by the soil population preferentially at all pH levels in both soils, there was a marked influence of pH on the quantity immobilized. Nitrogen immobilized from the ammonium source increased, as pH increased, whereas the reverse was true of the nitrate source. These results appear to be related to the physiological acidity or alkalinity of the nitrogen source.Most of the nitrogen incorporated into the organic fraction was present in the amino form.Contribution from the Department of Soils and Plant Nutrition University of California, Davis, and the Department of Vegetable Crops, University of California, Riverside. This work was supported in part by a grant from the National Science Foundation.     

Dietary boron intakes of selected populations in the United States

Knowledge of daily boron (B) intakes will assist researchers in establishing B requirements and elucidating the metabolic role of B in humans. B concentrations in commonly consumed foods were utilized to approximate the B intake of selected US populations. Triplicate food samples were digested at low temperatures with 16M HNO₃ and 30% H₂O₂, and analyzed by inductively coupled plasma spectroscopy (ICP). Milk and dairy products, juices, and beverages were the largest contributors to dietary B. Total B content of average daily diets ranged from 548 μg for toddlers (2 yr old) to 883 μg for mature males (60–65 yr old), excluding tap water contributions. Toddlers consumed 3.7 times more B than mature males when adjusted for body weight (body wt) and consumed the diet with the highest boron density (1.8 μg/kJ or 0.43 μg/kcal). Adolescent females consumed a diet with the lowest B density (1.12 μg/kJ or 0.26 μg/kcal). Food B concentrations applied to diet records (1020 μg/d) and ICP analysis of the corresponding food composites (1170 μg/d) were comparable (p < 0.05). Current estimations of B in US diets are consistent with reports in the literature stating that normal adult daily B intakes are approx 1 mg. Presented at the symposium “Second International Symposium on the Health Effects of Boron and Its Compounds” held in Irvine, CA, on October 23, 1997. This symposium was presented by the University of California, Irvine. The publication of the symposium was supported by U.S. Borax Inc. Guest editors for this symposium were B. Dwight Culver (University of California, Irvine, CA) and James R. Coughlin (Coughlin and Associates, Newport Coast, CA). US Department of Agriculture, Agricultural Research Service, Northern Plains Area is an equal opportunity/affirmative action employer, and all agency services are available without discrimination.     

Zn buffering capacity and Zn accumulation in Swiss chard for some sludge-amended soils

Zinc sorption by soils can greatly affect its availability to plants. This study was conducted to determine the relationship between the Zn sorption capacity and plant Zn accumulation in five sludge-amended soils using Swiss chard (Beta vulgaris L.) as an indicator plant. Zinc sorption as a function of Zn concentration and pH was determined for the soils which received no sludge amendment; also DTPA (diethylenetriaminepentaacetic acid) extractable Zn was determined in all soils. Whereas the responses of DTPA-Zn and plant Zn to pH and the quantities of Zn sorbed were similar, the logarithm of DTPA-Zn accounted for only 82% of the variability in the logarithm of Zn accumulation by the plants. The variability was better explained when pH was included with DTPA-Zn in stepwise multiple regressions. The Zn buffering capacity, defined as the ratio of the change in quantity of Zn sorbed ( Zn_s) to the change in Zn solution concentration (Zn₁) (or Zn_s/Zn₁), and the estimated quantity of Zn sorbed were used as a basis to measure Zn intensity. Zinc intensity, which reflects Zn solution concentration, was the predominant factor controlling Zn accumulation by Swiss chard, judging from the good fit of the values of both parameters to the Michaelis-Menten equation. The maximum Zn accumulation was approximately 9 mmol kg^–1.Scientific paper no. 8901-29, Department of Agronomy and Soils, College of Agriculture and Home Economics Research Center. Washington State University, Pullman, WA 99164, USA.Scientific paper no. 8901-29, Department of Agronomy and Soils, College of Agriculture and Home Economics Research Center. Washington State University, Pullman, WA 99164, USA.     

The response of trout and zebrafish embryos to low and high boron concentrations is U-shaped

Fish in the embryo-larval stage of development have been shown to be sensitive to boron (B) at both ends of the dose-response curve (1,2). The present study evaluated the health effects of low and high B concentrations on rainbow trout (Oncorhynchus mykiss), a cold water species, and zebrafish (Danio rerio), a warm water species. Rainbow trout embryos were incubated from day 1 until 2 wk posthatch in Type 1 ASTM ultrapure-grade water (12.5°C) supplemented with only B (0-500 μM) as boric acid, or together with CaCO₃ (0–2 mM) to increase water hardness. Embryonic growth was stimulated by B in a dose-dependent manner at all Ca concentrations (p < 0.001). Chronic exposures below 9 μmol B/L impaired embryonic growth and above 10 mmol B/L caused death (p < 0.001). Thus, the safe range of exposure for the rainbow trout was between the adverse effect concentrations of 9 μmol B/L and 10 mmol B/L. Zebrafish were maintained for 6 mo in ultrapure water containing <0.2 μmol B/L to determine the effect of low-level exposure. High-level exposure was assessed by exposing zygotes, derived from parents maintained at 46 μmol B/L, to graded concentrations of boric acid up to a concentration of 75 mmol B/L from fertilization until they were free feeding (96 h). Fertilization occurred, but zygotes failed to survive when water contained <0.2 umol B/L (p < 0.001). Death occurred at and above 9.2 mmol B/L. Thus, the safe range of B exposure for zebrafish was between the adverse effect concentrations of 0.2 μmol B/L and 9.2 mmol B/L. The dose-response for both species was thus U-shaped. Part of this work was previously published in abstract form and presented at Experimental Biology 97, April 6–9, New Orleans, LA (Eckhert, C. [1997] Embryonic trout growth and boron exposure,FASEB J. 11, A406 [abstract]).     

A combination method based on chitosan adsorption and duckweed (Lemna gibba L.) phytoremediation for boron (B) removal from drinking water

The metalloid boron (B) and its compounds widely exist in the environment, and boron can have hazardous effects on plants, animals, and human beings when it is found in high concentrations in water bodies. It is difficult and costly to remove B with conventional treatment methods from drinking water. Therefore, alternative and cost-effective treatment techniques are necessary. In this study, for the first time, a novel and environmentally friendly method based on the phytoremediation ability of chitosan and duckweed (Lemna gibba L.) combination was evaluated for B removal from drinking water. Our results from batch adsorption experiment indicated that the highest B uptake capacity of chitosan bead was found as 3.18 mg/g, and we determined the optimal B sorption occurs at pH value of 7. The Langmuir isotherm and pseudo-second-order kinetic model better fitted the equilibrium obtained for B removal. B in drinking water could be reduced to less than 2.4 mg L ^?1 when 0.05 g of plant-based chitosan beads and 12 L. gibba fronds were used in the 4-day treatment period.     

Turfgrass (Cynodon dactylon L.) sod production on sandy soils: II. Effects of irrigation and fertiliser regimes on N leaching

The effects of irrigation and fertiliser regimes on N leaching from the production of couch grass (Cynodon dactylon L.) sod, on a free-draining sandy soil, were evaluated in a 22-month field study. The experimental design used a randomised-block, split-plot design with three replicates. Main plots consisted of two irrigation treatments: 70 and 140% daily replacement of pan evaporation; four subplot fertiliser types (water-soluble (predominately NH₄NO₃), control-release, pelletised poultry manure and pelletised biosolids); and three N application rates (100, 200 and 300 kg N ha⁻¹ per crop). Nitrogen leaching was assessed by measuring the leachate volumes and concentrations of N species leached from soil lysimeters (250 mm in diameter by 950 mm in length) installed in 10 m² turfgrass plots. Nitrogen leaching ranged from 33 to 167 kg N ha⁻¹ over 22 months, depending upon the irrigation and fertiliser treatment. Irrigation treatment affected N leaching more than fertiliser treatment, and increasing the irrigation from 70 to 140% replacement of daily pan evaporation increased N leaching for all fertiliser types, and by up to four times. Forty six to 76% of losses occurred from the high irrigation treatments during the first 16 weeks after the turfgrass was planted as rhizomes. By contrast, N leaching did not appear to increase following harvest of sod. At the high irrigation treatment, N leaching was greater for the pelletised biosolids than the control-release; while at the low irrigation treatment, N leaching did not vary between fertiliser types. A significant proportion of the N leached was in the organic form. Therefore, we recommend total N and mineral N be measured when assessing N leaching from turfgrass. Nitrogen leaching from turfgrass production is low from all fertiliser types when the irrigation matches turfgrass water use and N is applied at a rate and frequency that approximates turfgrass requirements. Section Editor: P. J. Randall     

Effects of N application frequency on nitrogen uptake efficiency in Citrus trees

Two irrigation systems were used to compare nitrogen uptake efficiency in citrus trees and to evaluate the NO₃⁻ runoff in «Navelina» orange trees [Citrus sinensis (L.) Osbeck] on Carrizo citrange rootstock (Citrus sinensis × Poncirus trifoliata Raf.). These were fertilized with 125 g N as labelled K¹⁵NO₃ and grown outdoors in containers filled with a sand-loamy soil. Two groups of 3 trees received this N dose either in five equally split applications by a flooding irrigation system or in 66 applications by drip. Trees were harvested at the end of the vegetative cycle (December) and the isotopic ratios of ¹⁵N/¹⁴N were measured in the soil-plant system. The N uptake efficiency of the whole tree was higher with drip irrigation (75 percnt;) than with flooding system (64 percnt;). In the 0-90 cm soil profile, the N immobilized in the organic fraction was similar for both irrigation methods (around 13 percnt;), whereas the N retained as NO₃⁻ was 1 percnt; of the N applied under drip and 10 percnt; under flooding. In the last case, most of NO₃⁻ remained under root system and it could be lost to leaching either by heavy rainfalls or excessive water applications. These results showed that a drip irrigation system was more efficient for improving water use and N uptake from fertilizer, in addition to potentially reduced leaching losses.     

Effect of water stress on the boron response of wheat genotypes under low boron field conditions

Sterility has emerged as a widespread problem for wheat (Triticum aestivum) production in South and South-east Asia. Whilst boron (B) deficiency is commonly associated with sterility in wheat, the expression of sterility is complicated in rainfed conditions by a number of environmental factors including water stress. A field experiment was conducted to examine the effect of water stress on B response of wheat genotypes on a low B soil (0.087 mg B kg-1soil) at Chiang Mai, Thailand (18°45 N, 99° E) during the dry season from November to March. The experiment consisted of three factors arranged in a split-split plot design with two levels of irrigation: water stress (I–) and full irrigation (I+) in main plots, two levels of B: 0 kg (B0) and 1 kg B ha-1 (B+) as borax in sub plots and four wheat genotypes: SW 41, BL 1022, UP 262 and Sonora 64 in sub–sub plots. Water stress was applied by discontinuing irrigation in I– treatments after the double ridge stage. In all genotypes, above ground biomass was decreased by I–, but not by B deficiency. Significant B×genotype interactions were detected for reproductive growth. SW 41 and BL 1022 strongly responded to added B with relief from B deficiency symptoms at anthesis and improved grain set index (GSI), grains ear-1, ears with grain and grain yield at maturity. By contrast, Sonora 64 could set grain well at B0 and did not show any response to added B with respect to these parameters. Grains ear-1 of SW 41 and BL 1022 was not affected by full irrigation at B0, but were significantly increased when fully irrigated with added B. In all genotypes, B concentration of the flag leaf and the ear at booting and at anthesis was significantly higher in B+, but was not affected by irrigation. Boron × irrigation interactions detected in this study indicate the possibility of the influence of water stress on the severity of wheat sterility in South and South-east Asia.     

The epiphytology of spearmint rust in Indiana

Summary Field studies indicated that subterranean aecia ofPuccinia menthae Pers. are of little significance in the initiation of spearmint rust infection in undisturbed fields. Also, wild or escaped mints do not appear to be of significance. The primary source of inoculum comes either from fields that are not fall plowed or from infected rhizomes or transplants during spring planting. Temperatures during May appear to be critical in the development of rust epiphytotics. The predominant race of the pathogen occurring in Indiana corresponds to Race 1.Respectively, former graduate research assistant, Department of Botany and Plant Pathology, Purdue University, presently Assistant Plant Pathologist, University of Arizona, Mesa Branch Experiment Station, Mesa, Arizona; and Associate Plant Pathologist, Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana. Journal paper 2691. The authors thank Dr.M. J. Murray, A. M. Todd Company, Kalamazoo, Michigan, for species ofMentha used as race differentials. This research was supported, in part, by funds provided through the Mint Industries Research grant.     

Sorption of dissolved organic matter by mineral soils of the Siberian forest tundra

Because of low net production in arctic and subarctic surface water, dissolved organic matter (DOM) discharged from terrestrial settings plays an important role for carbon and nitrogen dynamics in arctic aquatic systems. Sorption, typically controlling the export of DOM from soil, may be influenced by the permafrost regime. To confirm the potential sorptive control on the release of DOM from permafrost soils in central northern Siberia, we examined the sorption of DOM by mineral soils of Gelisols and Inceptisols with varying depth of the active layer. Water‐soluble organic matter in the O horizons of the Gelisols was less (338 and 407 mg C kg^?1) and comprised more dissolved organic carbon (DOC) in the hydrophobic fraction (HoDOC) (63% and 70%) than in the O horizons of the Inceptisols (686 and 706 mg C kg^?1, 45% and 48% HoDOC). All A and B horizons from Gelisols sorbed DOC strongly, with a preference for HoDOC. Almost all horizons of the Inceptisols showed a weaker sorption of DOC than those of the Gelisols. The C horizons of the Inceptisols, having a weak overall DOC sorption, sorbed C in the hydrophilic fraction (HiDOC) stronger than HoDOC. The reason for the poor overall sorption and also the preferential sorption of HiDOC is likely the high pH (pH>7.0) of the C horizons and the smaller concentrations of iron oxides. For all soils, the sorption of HoDOC related positively to oxalate‐ and dithionite–citrate‐extractable iron. The A horizons released large amounts of DOC with 46–80% of HiDOC. The released DOC was significantly (r=0.78, P<0.05) correlated with the contents of soil organic carbon. From these results, we assume that large concentrations of DOM comprising large shares of HiDOC can pass mineral soils where the active layer is thin (i.e. in Gelisols), and enter streams. Soils with deep active layer (i.e. Inceptisols), may release little DOM because of more frequent infiltration of DOM into their thick mineral horizons despite their smaller contents of reactive, poorly crystalline minerals. The results obtained for the Inceptisols are in agreement with the situation observed for streams connecting to Yenisei at lower latitudes than 65°50′ with continuous to discontinuous permafrost. The smaller sorption of DOM by the Gelisols is in agreement with the larger DOM concentrations in more northern catchments. However, the Gelisols preferentially retained the HoDOC which dominates the DOC in streams towards north. This discrepancy can be explained by additional seepage water from the organic horizons that is discharged into streams without intensive contact with the mineral soil.     

The control of boron accumulation by two genotypes of wheat

The mechanism of boron (B) uptake in wheat was studied using two genotypes with known differences in their ability to accumulate B. Influx and efflux of B was measured in the roots of intact 21 d old plants.Roots grown in 15 M B, when transferred to solutions containing 1mM B showed a rapid increase in B content for up to 60 min, after which no further increase was evident up to 4 h. No genotypic difference in B influx was apparent over these time periods. Roots grown in 1mM B for 7 d and then rinsed in B-free solutions quickly lost most of B that they contained within 1 hour; little further efflux was observed over the following three hours. As with the influx, no genotypic difference in B flux was evident.It is suggested that the lack of genotypic difference in the short-term B fluxes could be due to a masking effect of extracellular B bound in the cell walls of the roots.Department of Botany, University of Adelaide