Soil Boron Research Articles

Plant availability of boron in acid soils as assessed by different extractants

AbstractEstimation of available‐boron (B) status through conventional methods in B‐deficient acidic Inceptisols and Entisols is often hampered because of their very low B content. In the present study, the extractability of available B by different extractants was tested in relation to soil properties. Plant availability of B was assessed with mustard (Brassica campestris L.) and wheat (Triticum aestivum L.) in pot experiments. Twelve soils with varying characteristics were extracted for available B with hot water (HW), hot CaCl2 (HCC), KH2PO4 (PDP), tartaric acid (TA), and mannitol‐CaCl2 (MCC). Mustard (cv. B‐9) and wheat (cv. PBW‐343) were grown with four levels of B (0, 0.25, 0.50, and 1.0 mg [kg soil]–1). Dry‐matter accumulation and B concentrations were determined at pre‐flowering and full‐maturity stages for mustard and at panicle‐initiation and maturity stages for wheat. The extraction of B from the soils ranked HCC > HW > PDP > TA > MCC. The higher extractability with HW and HCC was likely due to higher temperature and that of PDP because of its phosphorus content, which facilitated the desorption of B. The low B extraction with MCC resulted from the poor mannitol‐B complex formation in acidic soils. The application of B increased dry‐matter accumulation, plant B concentration, and uptake at all B levels and growth stages in both crops with the responses being more pronounced during the early developmental stage. Based on linear correlations, Mallow's Cp statistics, and principal‐component analyses, HCC and HW were the best extractants for estimating available B in the acidic experimental soils.

Mehlich 3 Extraction of Boron in Boron Treated Soils as Compared to Other Extractants

Hot water extraction (HW) is time‐consuming, highly variable, and losing popularity as the standard method for estimating plant‐available boron (B) in soil. Proposed alternatives are not widely used and guesstimation is replacing assessment at many soil test facilities. Mehlich 3 is increasingly promoted as a universal extractant, and diethylenetriaminepentaacetic acid (DTPA)–sorbitol and pressurized hot water (PHW) are effective and comparable to hot water extraction but also simpler and easier. Mehlich 3 B extraction has been compared mainly to hot water extraction. Because Mehlich 3 usage would be limited to neutral to acid soils, this study used a limed acid Darco loamy fine sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudult) from eastern Texas to which 10 rates of B were applied followed by either incubation without plants or planting to alfalfa in greenhouse pots. Mehlich 3 extraction of soils obtained from a long‐term experiment on Darco soil from which alfalfa yield response has already been related to hot water, DTPA–sorbitol, and PHW is reported. The purpose was to determine the efficiency of Mehlich 3 B extraction compared to hot water, PHW, and DTPA–sorbitol in these B‐fertilized soils. Mehlich 3–extractable B significantly correlated with the rate of B application to incubation, greenhouse, and field soils and with B concentration and total B uptake in alfalfa in a greenhouse experiment. However, yield responses to B application were not observed in the greenhouse study. In the field where B response to B application was observed, Mehlich 3–extractable B did not correlate with alfalfa yield, whereas hot water and pressurized hot water did. In considering Mehlich 3 for B extraction, be aware that some older inductively coupled plasma (ICP) models may have significant drift when B is measured in Mehlich 3 extractant. In the current study, this problem was overcome with a new model instrument. Although effective in estimating B levels imposed on soils by fertilizer application, Mehlich 3 could not predict yield and thus cannot currently be recommended as a “universal” extractant to include B.

Response of apple trees to boron fertilization under conditions of low soil boron availability

The aim of the study was to examine the effect of boron (B) fertilization on the vegetative and the reproductive responses of apple ( Malus domestica Borkh.) trees grown at low soil B availability. The experiment was carried out in 2005 under a greenhouse on 5-year-old ‘Jonagold’ apple trees/M.9 EMLA planted singly in 50-L containers filled with a sandy loam soil with hot water-soluble B concentration of 0.32 mg kg −1. The trees were fertilized with B as foliar or soil application. Foliar B sprays were applied at the stage of pink bud, beginning of flowering, petal fall, and 10 days after flowering, at a solution concentration of 0.03%. Soil B fertilization was done at the bud break stage at a rate of 2 g per tree (27 mg B kg −1 soil). The trees untreated with B served as the control. The results showed that soil B fertilization improved root development and tree vigor. Leaves of trees supplied with B to the soil had higher B concentration and chlorophyll, net photosynthetic rate, stomatal conductance, and activity of catalase and glutathione reductase than those of the control plants. Boron fertilization, regardless of application mode, increased fruit yield; the efficiency of foliar B sprays was higher than soil B application. Apple fruits of trees fertilized with B to the soil were bigger, more colored, richer in B, and had higher soluble solids concentration, and titratable acidity compared to those of the control trees.

Widespread Deficiencies of Sulfur, Boron, and Zinc in Indian Semi-Arid Tropical Soils: On-Farm Crop Responses

ABSTRACT On-farm studies were conducted during 2002–2004 to determine fertility status, including sulfur (S) and micronutrients, and crop response to fertilization on farmers' fields in the semi-arid zone of India. Nine hundred-twenty four soil samples taken from farmers' fields, spread in the three districts of Andhra Pradesh (India), were analyzed for soil chemical fertility parameters. Results showed that samples were low in organic carbon (C), total nitrogen (N), and low to moderate in extractable phosphorus (P), but adequate in available potassium (K). Analyses of soil samples for extractable S and micronutrients was most revealing and showed that 73–95% of the farmers' fields were deficient in S, 70–100% in boron (B), and 62–94% in zinc (Zn). On-farm trials conducted during three seasons (2002–2004) showed significant yield responses of maize, castor, groundnut, and mung bean to the applications of S, B, and Zn. The yield responses were larger when S, Zn, and B were applied along with N and P. Applications of S, B and Zn also significantly increased the uptake of N, P, K, S, B, and Zn in the crop biomass. Results show widespread deficiencies of S, B, and Zn under dryland agricultural conditions; results also show that the nutrient deficiencies can be diagnosed by soil testing. It was concluded that the drylands in the semi-arid regions of India were not only thirsty (water shortage), but also hungry (nutrient deficiencies).

Boron removal from geothermal waters by electrocoagulation

Most of the geothermal waters in Turkey contain extremely high concentration of boron when they are used for irrigation. The use of geothermal waters for irrigation can results in excess amount deposition of boron in soil. On the other hand, a minimal boron concentration is required for irrigational waters. In this study, electrocoagulation (EC) was selected as a treatment process for the removal of boron from thermal waters obtained from Ilıca-Erzurum in Turkey. Current density (CD), pH of solution and temperature of solution were selected as operational parameters. The results showed that boron removal efficiency increased from pH 4.0 to 8.0 and decreased at pH 10.0. Although boron removal efficiency was highest at pH 8.0, energy consumption was very high at this pH value compared to other pH intervals. Boron removal efficiency reached to 95% with increasing current density from 1.5 to 6.0 mA/cm 2, but energy consumption was also increased in this interval. At higher temperatures of solution, such as 313 and 333 K, boron removal efficiency increased. At optimum conditions, boron removal efficiency in geothermal water reached up to 95%.

Fine mapping and targeted SNP survey using rice-wheat gene colinearity in the region of the Bo1 boron toxicity tolerance locus of bread wheat

Toxicity due to high levels of soil boron (B) represents a significant limitation to cereal production in some regions, and the Bo1 gene provides a major source of B toxicity tolerance in bread wheat (Triticum aestivum L.). A novel approach was used to develop primers to amplify and sequence gene fragments specifically from the Bo1 region of the hexaploid wheat genome. Single-nucleotide polymorphisms (SNPs) identified were then used to generate markers close to Bo1 on the distal end of chromosome 7BL. In the 16 gene fragments totaling 19.6 kb, SNPs were observed between the two cultivars Cranbrook and Halberd at a low frequency (one every 613 bp). Furthermore, SNPs were distributed unevenly, being limited to only two genes. In contrast, RFLP provided a much greater number of genetic markers, with every tested gene identifying polymorphism. Bo1 previously known only as a QTL was located as a discrete Mendelian locus. In total, 28 new RFLP, PCR and SSR markers were added to the existing map. The 1.8 cM Bo1 interval of wheat corresponds to a 227 kb section of rice chromosome 6L encoding 21 predicted proteins with no homology to any known B transporters. The co-dominant PCR marker AWW5L7 co-segregated with Bo1 and was highly predictive of B tolerance status within a set of 94 Australian bread wheat cultivars and breeding lines. The markers and rice colinearity described here represent tools that will assist B tolerance breeding and the positional cloning of Bo1.

Influence of parent material on the contents and distribution of B and Zn in upland soils of Bauchi State, Nigeria

A study was conducted to determine the influence of parent material on the contents and distribution of boron and zinc in soils of Bauchi State, Nigeria. Fourty nine, 30, and 20 top 0–30cm soil samples developed from basement complex rock, Kerri-Kerri Formation and Chad Formation, respectively, were collected and analysed using standard laboratory procedures. Results obtained indicate that parent material influenced Zn but not B contents in the soils. Generally, both B and Zn varied widely (CV>30%) between locations in the State, irrespective of the parent material. Organic carbon significantly (P<0.01) and negatively correlated with Zn in soils from BCR (r = −0.410) and CF (r = −0.563) and positively with B in soils developed from KKF (r = 0.471) and CF (r = 0.345). With means of 0.41 and 1.46 mgkg−1 for B and Zn respectively, their contents are considered adequate for crop growth. Crops grown on soils in some localized areas identified with values below the critical limits for these micronutrients may, however, benefit from their application.

Structure and Mn 2+ adsorption properties of boron-doped goethite

Two kinds of boron-doped goethites were synthesized, one was called ad-B-goethite prepared by reacting the original goethite with borax solution and the other called oc-B-goethite prepared in the presence of boric acid solution. The goethites were characterized by IR and XRD. The IR bands of Fe OH Fe in-plane bending and free OH of the boron-doped goethites were weak compared with the original goethite. The IR bands of bending modes of trigonal and tetrahedral B were found in ad-B-goethite (420 cm − 1 ) and oc-B-goethite (527 cm − 1 and 476 cm − 1 ). These results suggest that some hydroxyl groups were replaced by the introduced boron. Analysis of XRD patterns indicated ad-B-goethite remained the characteristic of α-FeOOH, while oc-B-goethite did not. The specific surface areas of these goethites using BET method were 108 m 2/g, 89 m 2/g and 120 m 2/g for the original goethite, ad-B-goethite and oc-B-goethite, respectively. The relatively large surface area of oc-B-goethite indicated the likelihood of higher activity than the original goethite, which was supported by evidence of the higher Mn 2+ adsorption ability of oc-B-goethite. The amount of adsorbed Mn 2+ increased with pH by the geothites and the order of Mn 2+ adsorption capability was oc-B-goethite > ad-B-goethite > the original goethite. It was suggested that boron in soils not only serves as a plant nutrient, but can also decreases the Mn 2+ toxicity through the function of enhancing Mn 2+ adsorption in acidic soils.

Effects on Environment and Agriculture of Geothermal Wastewater and Boron Pollution in Great Menderes Basin

Boron toxicity is an important disorder that can be limit plant growth on soils of arid and semi arid environments through the world. High concentrations of Boron may occur naturally in the soil or in groundwater, or be added to the soil from mining, fertilizers, or irrigation water. Off all the potential resources, irrigation water is the most important contributor to high levels of soil boron, boron is often found in high concentrations in association with saline soil and saline well water. Although of considerable agronomic importance, our understanding of Boron toxicity is rather fragment and limited. In this study, Boron content of Great Menderes River and Basin was researched. Great Menderes Basin is one of the consequence basins having agricultural potential, aspect of water and soil resources in Turkey. Great Menderes River, water resource of the basin was to be polluted by geothermal wastewater and thermal springs including Boron element. Great Menderes Basin has abundant geothermal water resources which contain high amounts of Boron and these ground water are brought to surface and used for various purposes such as power generation, heating or thermal spring and than discharged to Great Menderes River. In order to prevent Boron pollution and hence unproductively in soils, it is necessary not to discharged water with Boron to irrigation water. According to results, it was obtained that Boron content of River was as high in particular Upper Basin where there was a ground thermal water reservoir. Boron has been accumulated more than plant requirement in this area irrigated by this water. Boron content of River was relatively low in rainy months and irrigation season while it was high in dry season. Boron concentration in the River was to decrease from upstream to downstream. If it is no taken measure presently, about 130,000 ha irrigation areas which was constructed irrigation scheme in the Great Menderes basin will expose the Boron pollution and salinity. Even though Boron concentration of river water is under 0.5 ppm limit value, Boron element will store in basin soils, decrease in crop yields, and occur problematic soils in basin.

Extraction and Determination of Hot-Water-Soluble Boron in Soils

Extraction and Determination of Hot-Water-Soluble Boron in Soils

Whole plant response of crop and weed species to high subsoil boron

Within the semi-arid region of south-eastern Australia, high levels of subsoil boron (B) in alkaline soil can limit production of dryland crops. The aim of this research was to investigate the whole plant response to a range of subsoil-extractable B concentrations for a number of crop and weed species common to agricultural areas of South Australia. Specifically, the objectives were to determine (a) the morphological response of the entire root system to high subsoil B and (b) the available B concentrations in subsoil critical for expression of shoot traits commonly used in selection of B tolerance. Barley grass (Hordeum glaucum L.), crop barley (Hordeum vulgare) variety Clipper and breeders’ line VB9953, fababean (Vicia faba var. Fjiord), Lincoln weed (Diplotaxis tenuifolia L.), prickly lettuce (Lactuca serriola), and evening primrose (Oenothera stricta L.) were grown in sealed PVC cylinders (500 mm deep by 150 mm diam.) containing a sandy soil. The concentration of extractable B in the topsoil (0–0.20 m), considered non-toxic, was 0.5 mg/kg for all cylinders but a range of B treatments (0.5, 2.4, 4.3, 6.8, or 12.2 mg/kg) was applied directly to the subsoil (0.30–0.50 m). Increasing the concentration of extractable B in the subsoil decreased root dry weight in this region, but did not reduce water use from subsoil by barley grass or evening primrose. The response of the roots in the topsoil and subsequent responses in the shoot also differed among species. Symptoms of B toxicity in shoots of all the species were observed at subsoil-extractable B concentrations of 12.2 mg/kg and at lower concentrations in some of the crop and weed species. Shoot growth, total water use, and root growth in topsoil of Clipper and Lincoln weed were severely impaired by high subsoil-extractable B, as was topsoil root growth in evening primrose, with the reduction in the weed species being mostly associated with a decrease in taproot dry weight. Barley grass, VB9953, evening primrose, and to a lesser extent fababean and prickly lettuce, maintained shoot growth at all subsoil-extractable B concentrations, despite a reduction in subsoil water use by VB9953. Prickly lettuce and VB9953 also sustained root growth in the topsoil whilst fababean and barley grass increased root growth in the topsoil in response to high subsoil extractable B. There was no direct relationship between the quantity of B accumulated in shoots and detrimental effects on growth. Furthermore, there appeared to be no direct relationship between water uptake and B uptake since irrespective of the effect of subsoil B on either subsoil or total water use, shoot B concentration increased in all the species/genotypes as subsoil B increased. The degree to which plants were deemed to exhibit tolerance was, therefore, highly dependent upon the trait used for assessment. One suggestion in the current study is that shoot dry matter in B toxic soil can be a consistent parameter for considering varieties for tolerance to B toxicity.

Physiological mechanisms of tolerance to high boron concentration in Brassica rapa.

Tolerance to high boron concentration in Brassica rapa was primarily due to low net boron uptake by the roots. However, in the two tolerant genotypes, 39-43% of boron uptake was retained in the tap roots, which limited boron accumulation in the leaves, and also contributed to boron tolerance. In the sensitive genotype, 99% of the increase in boron uptake caused by high soil boron accumulated in the leaves, particularly in the leaf margins. Despite higher transpiration rates, lower net boron uptake occurred in the tolerant genotypes. This result cannot be explained by passive boron uptake alone. Active boron efflux was probably responsible for differences in net boron uptake among tolerant and sensitive genotypes. Boron concentration was much lower in the cell walls than in the cell sap of leaves, indicating that storage of boron in the cell walls was not a tolerance mechanism. Despite high boron concentrations in the leaf symplasm, rates of photosynthesis, transpiration and growth were almost unaffected in the tolerant genotypes. The results demonstrate that boron tolerance in Brassica rapa involves boron exclusion at the root level, boron partitioning away from leaves and, as boron accumulates in leaves despite the first two mechanisms, boron tolerance of the leaf tissue itself.

Response of ‘Bluecrop’ Highbush Blueberry to Boron Fertilization

ABSTRACT The objective of this experiment was to examine the vegetative and generative responses of highbush blueberry to boron fertilization. The study was carried out in 2002–2003 in Central Poland on mature ‘Bluecrop’ blueberries (Vaccinium corymbosum L.) planted at a spacing of 3 × 1 m on a sandy loam soil with pH value of 3.9 and low hot water soluble boron status. Blueberries were soil- or foliar-supplied with boron. Foliar boron sprays were done four times per season: at the beginning of blooming, at petal fall, and three and six weeks after the ending of flowering. In each spray treatment, boron was applied at a rate of 0.2 kg ha−1. Soil boron was applied at the stage of bud break at a rate of 2 kg ha−1. Plants untreated with boron served as control. The results showed that boron fertilization increased boron levels in flower and leaf tissues. This treatment, regardless of boron application mode, did not affect plant vigor, the number of flowers per cane, fruit set, nor yield. Also mean fruit weight and berry firmness were not influenced by boron fertilization. Fruit of boron-supplied blueberries had higher soluble solids concentrations than those of the control plants. It is concluded that boron requirements of highbush blueberry are relatively low compared to most fruit crops and that critical leaf boron concentrations of ‘Bluecrop’ blueberry are below 15 mg kg−1 DW.

On-line generation and hydrolysis of methyl borate for the spectrophotometric determination of boron in soil and plants with azomethine-H

A continuous-flow system for boron determination in soils and plants with spectrophotometric detection using the azometihine-H-boron complex method was developed. In order to avoid the interferences of concomitants present in samples and to increase the sensitivity, the element was separated on-line from the matrix by methyl borate generation. For this purpose, a concentrated sulfuric acid sample solution was combined with methanol in 1:3 ratio which produce enough heating for the esterification reaction without external source. Subsequently, the methyl borate produced was stripped by the addition of a nitrogen flow and separated from the bulk solution in a gas–liquid separator to be then hydrolyzed in an ammonium-phosphate buffer solution (pH 6.8). Finally, the new bulk of phases were separated in a second gas–liquid separator and the liquid phase was combined with azomethine-H to form a boron complex for its detection at 420 nm. The effects of a number of possible interferents, both anionic and cationic were evaluated. The most severe depressions were caused by fluoride and potassium for which a concentration of 100 μg ml −1 caused a 5% depression on the signal. A linear response was obtained between the detection limit of 0.05 μg ml −1 (3 σ of the blank) and 50 μg ml −1 of boron. The precision (R.S.D.%) for 10 consecutive readings of the same solution (5.0 μg ml −1 of boron) was 2.6%. Recoveries of boron added to the samples before the extraction process were 94, 97, and 101% for soil, fruit tissue, and leaf tissue, respectively. The developed system was applied to the determination of boron in soil, fruits tissue, and leaves tissue of coffee plantations from different towns of Mérida State, Venezuela.

Pressurized Hot Water and DTPA‐Sorbitol as Viable Alternatives for Soil Boron Extraction. II. Correlation of Soil Extraction to Responses of Boron‐Fertilized Alfalfa

Pressurized hot water and DTPA‐Sorbitol are two relatively new, proposed alternative soil boron (B) extraction methods for which no data on yield or plant nutrient uptake have been reported for validation. Both methods initially have shown significant correlation with the hot water extraction method in untreated soils as well as soils incubated with various levels of B. The objective of the research was to extract samples of B‐treated soils by using all three extraction methods and correlate the B values obtained to yield, B tissue concentration, and total B removal of alfalfa (Medicago sativa). Greenhouse and field experiments on alkaline and limed acid soils naturally low in hot water‐extractable B were conducted to test alfalfa response to B fertilizer. In the greenhouse, highly significant relationships exist between plant uptake and extractable B with all three methods at varying levels of applied B, but no alfalfa yield response was observed. All three methods result in accurate predictions of plant B tissue concentrations and total B removal. The field experiment exhibited a significant positive relationship between total alfalfa yield and extractable B using hot water and pressurized hot water extractions. Extractable B using DTPA‐Sorbitol was not related to total alfalfa yield in the field experiment. This work, coupled with the earlier incubation studies, supports the pressurized hot water extraction method as an improvement over hot water in diverse soil types. The lack of relationship in the acid soil supports DTPA‐Sorbitol as an improvement over hot water in alkaline soils.

Pressurized Hot Water and DTPA‐Sorbitol as Viable Alternatives for Soil Boron Extraction. I. Boron‐Treated Soil Incubation and Efficiency of Extraction

Serious challenges associated with hot water extraction, the standard extraction method for water‐soluble boron (B), limit its use in commercial soil‐testing laboratories. Several alternatives to make B testing more practical have been proposed and studied; none of the alternatives have readily replaced the hot water method. Two relatively new, promising B extraction methods are pressurized hot water and DTPA‐Sorbitol. Very little reported work compares B extraction values obtained from the standard hot water extraction method and these two alternative methods. This study was conducted to complete an initial step in validating new procedures—extracting the designated nutrient from fertilized, incubated soils by using standard and alternative extraction methods and comparing the resulting values. The three extraction methods were used to extract B from samples of calcareous sand and silt loam soils and limed, loamy fine sand, all which had been treated with 10 levels of B (0–8 mg kg−1) and incubated for 7 and 28 days. The amount of B extracted increased as the rate of B application increased with all three soil‐extraction methods. High correlations (r 0.977–0.999) were observed between extractable B and rate of B application with all three procedures. Correlations between the amount of extractable B using hot water extraction and the value obtained with an alternative extraction method were similar for both methods (r=0.89). Hot water generally extracted the least and pressurized hot water the most B regardless of soil type, rate of application, or duration of incubation. This study suggests the more easily used methods of pressurized hot water and DTPA‐Sorbitol could be recommended as replacements to the cumbersome hot water extraction.

The response of antioxidant enzymes of three soybean varieties to molybdenum and boron in soil with a connection to plant quality

The response of antioxidant enzymes and quality of three soybean varieties to Mo and/or B in soil has been studied in this paper. Pot experiments were set up with four treatments (control, +Mo, +B, +[Mo + B]) at four growth stages. The study showed that Mo and/or B increased antioxidant enzyme activities and protein content in the seeds. The variation and interaction between Mo and B in soil was explored with regard to their impact on the soybean quality. The Mo and/or B decreased oil-content, linoleic and linolenic acid and thus improve plant quality for human health. There were some dissimilarity in antioxidant enzymes and quality of plant between supplement of Mo and B in the soil, and the interrelation between Mo and B in the plant was co-supplementary to each other. Therefore, the quality of the soybean with Mo and B treatments was much improved than those with Mo or B alone. The study shows that the quality of soybean seeds has some stability as compared to physiological and growth characteristics of vegetative organs.

Maize Growth and Changes in Soil Fertility After Irrigation with Treated Sewage Effluent. II. Soil Acidity, Exchangeable Cations, and Sulfur, Boron, and Heavy Metals Availability

The objective of this research was to study the effects of maize irrigation with secondary‐treated sewage effluent (STSE) on soil pH, electrical conductivity (EC), and on the available soil concentrations of calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), aluminum (Al), sulfur (S), boron (B), and of heavy metals and to investigate the plant element accumulation, except for Al. The treatments consisted of mineral fertilization and irrigation with the STSE. After 58 days, maize plants were harvested, and soil and plant were analyzed. The STSE effectively reduced the mineral nitrogen fertilizer soil‐acidifying effect, induced increases in the EC, and in the base saturation, and did not significantly alter the available concentrations of S, B, and heavy metals. The STSE irrigation did not affect the shoot S, B, copper (Cu), iron (Fe), and manganese (Mn) contents in plants properly fertilized, but it induced a decrease in shoot zinc (Zn) content. Sodium was the most affected element by the STSE irrigation.

The effect of molybdenum and boron in soil on the growth and photosynthesis of three soybean varieties

This paper presents a study on growth and photosynthesis response of soybean to Mo and/or B in soil. Pot experiments were set up to examine the effect of Mo and/or B on growth and photosynthesis of three soybean varieties with four treatments (control, +Mo, +B, +[Mo + B]) at various growth stages. The study showed that Mo and/or B increased main length, system volume and dry weight of the roots, aboveground biomass, leaves&amp;rsquo; photosynthesis rate of soybean. The variation and interaction between Mo and B in soil was explored with regard to their impact on soybean growth and photosynthesis. There were some dissimilarity in growth and photosynthesis in the plants between the supplements of Mo and B in the soil, and the interrelation between Mo and B in plant and was co-supplementary to each other. Therefore, growth and photosynthesis of the soybean with Mo and B treatments were much more improved than those with Mo or B alone. Besides, some genotypic variation was found in three soybean varieties, in which Zhechun III was the most sensitive and 3811 the most tolerant plant to Mo and B.

Chemical fractionation of boron and heavy metals in soils irrigated with wastewater in central Mexico

Abstract The aim of the present work was to evaluate the accumulation of selected trace elements (boron, cadmium, chromium, mercury, lead and arsenic) in agricultural soils of the Zone 1 of the Irrigation District 03 (DR03) in the State of Hidalgo, Mexico. The soils of Zone 1 have, on average, been irrigated with raw wastewater for about 20 years (range 6–41 years). A clear positive correlation between the organic carbon contents in soils and the irrigation time was found. The total concentrations of the elements analysed were 0.51–1.89 mg Cd kg−1, 11.59–27.42 mg Cr kg−1, 3.99–47.08 mg Pb kg−1 and 9.2–123.8 mg B kg−1. Samples of topsoils (0–30 cm) were extracted using a modified Tessier method according to a six fraction scheme: easily soluble (F0), exchangeable (F1), bound to carbonates (F2), associated with oxides of iron and manganese (F3), bound to organic matter and sulphides (F4), and the residual fraction (F5). In general, the elements were distributed in the fractions F0, F4, and F5. The concentrations of total arsenic and mercury were below the detection limits (0.03 and 0.01 mg kg−1, respectively) except for 0.77 mg Hg kg−1 in one soil. The concentrations of total Cr and Pb did not exceed the maximum permissible levels set by the regulations of the European Union whereas total Cd was on the verge. A linear increase between the total metal concentrations and the irrigation time was found. In this study several crops harvested from soils showed Cd and Pb contents higher than those recommended by the Dutch and German guidelines. It can be concluded that the soils may pose a potential risk to the trophic chain and effective restrictions for the cultivation of crops that are sensitive to or known to accumulate heavy metals (i.e. nopal, onions, garlic, lettuce, potatoes, beets, and turnips) should be considered.