Boron in soil

Moghe V.B., Mathur G.M. Status of boron in soil arid soils of western Rajasthan. Soil Sc iPlantNutr 1966 12 11-14. 

Spectrophotometric methods have been used to determine water soluble boron in soils. In one method [1] the soil is extracted with boiling water then converted to fluoroborate which is evaluated spectrophotometrically as the methylene blue complex. 

Aznarez et al. [2] have described a Spectrophotometric method using curcumin as chromopore for the determination of boron in soil. Boron is extracted from the soil into methyl isobutyl ketone with 2-methylpentane-2,4-diol. In this method 0.2-lg of finely ground soil is digested with 5ml concentrated nitric-perchloric acid (3 + 1) in a polytetrafluoroethylene lined pressure pump for 2h at 150°C. The filtrate is neutralized with 6M sodium hydroxide and diluted to 100ml with hydrochloric acid 1+l.This solution is triple extracted with 10ml of methyl isobutyl ketone to remove iron interference. This solution is then extracted with 10ml 2-methyl pentane-2,4 diol and this extract dried over anhydrous sodium sulphate. 

Table 12.2 Determination of boron in soils by the spectrophotometric method...

A further spectrophotometric method [3, 4] for water soluble boron in soil, boron is extracted from soil with boiling water. Borate in the extract is converted to fluoroborate by the action of orthophosphoric acid and sodium fluoride. The concentration of fluoroborate is measured spectrophotometrically as the blue complex formed with methylene blue and which is extracted into 1, 2-dichloroethane. Nitrates and nitrites interfere they are removed by reduction with zinc powder and orthophosphoric acid. 

Inductively coupled plasma optical emission spectrometry has been applied to the determination of boron in soil extracts in amounts down to 0.5m L 1 [5]. 

Boron exists in several forms in the soil (USEPA 1975) in soil solntion, it exists largely as the undissociated weak monobasic acid that accepts hydroxyl gronps (Gnpta and Macleod 1982). Most plant-available boron in soils is associated with soil organic matter (Gnpta and Macleod 1982), with the hot-water soluble boron fraction (Hingston 1986), and with soil solntion pH ranges of... 

Fig. 3.8. EfFect of temperature on the leaching of boron in soil in the presence (Su) and absence (S) of ultrasounds. For details, see text. (Reproduced with permission of Elsevier.)...

D.-H. Chen, F. Lazaro, M.D. Luque de Castro, M. Valcarcel, Direct spectrophotometric determination of total boron in soils with ultrasonic leaching in automatic flow systems, Anal. Chim. Acta 226 (1989) 221. 

Garcia-Campana am, Barrero FA and Ceba MR (1992) Spectrofiuorimetric determination of boron in soils, plants and natural waters with alizarin red S. Analyst (London) 117 1189-1191. 

A review paper covering forms of boron in soils, interactions between soil solution boron and adsorbed boron, adsorption-desorption processes, and relationships to plant nutrition is presented. Diagnostic criteria are given for chemical analysis of soils and irrigation waters in terms of boron status, i.e., deficient, adequate, or excessive, and specified according to crop species group. The potential boron hazard of municipal sewage effluents to water supplies is discussed. 

Boron in Organic Matter. Although much of the boron in soils is associated with minerals resistant to weathering (3), boron is also contained in the organic fraction of soils. Little is known, however, of the reactions and availability of boron in soil organic matter other than that the quantity is small and is restricted to the surface horizon of soils primarily. As this organic matter fraction mineralizes, the boron redistributes in the soil-water system, becoming available in part for plants (10). 

A serious limitation of such boron criteria is the lack of provision for difference in soils, irrigation management, and climate. Soils differ in their capacity for adsorbing boron, and irrigation and rainfall characteristics likewise exert an effect on the distribution of available boron in soils. Additional details are presented in discussions of criteria for irrigation water quality by Bernstein (41) and Rhoades (42). 

In this case, the mean garden level (1.81 ppm) is only about two and a half times as great as the rural arable level (0.70 ppm), but the difference is perhaps more serious since some of the levels encountered could have deleterious effects on plant growth. The range of concentration of water-extractable boron in soils over which plants will grow normally is unusually narrow because of the ease with which water-soluble boron is taken up by plants [131]. On the other hand, available boron is largely present in the soil as soluble borates, so that contaminant boron is readily leached out of the soil. 

The average concentration of boron in the earth s CTust is 17 ppm, and most soils fall within the range of 3-100 ppm. Boron occurs in high concentrations in sedimentary rocks and in clay-rich marine sediment due to the relatively high concentration of boron in seawater. Deposits of boron are found in association with volcanic activity and where marshes or lakes have evaporated under arid conditions. Coastal soils contain up to 50 times as much boron as do inland soils while, generally, humid soils are lower in boron content than slightly leached soils. The concentration of boron in soil is influenced also by the presence of other minerals, and soil pH and texture (Butterwick et al., 1989 Steinnes, 2009). 

HARADA T. and TAMAI M. 1968. Factors affecting behaviour of boron in soil 1. Some soil properties affecting boron adsorption of soil. Soil Science and Plant Nutrition, 14, 215-224. 

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