H. S. Forster

Factors Affecting Molybdenum Adsorption By Soils And Minerals

Molybdenum adsorption behavior was investigated on a variety of crystalline and X-ray amorphous aluminum and iron oxide minerals, clay minerals, and arid-zone soils as a function of solution pH, molybdenum concentration, ionic strength, particle concentration, competing anion concentrations, and

BORON SORPTION ON CALCAREOUS SOILS AND REFERENCE CALCITES

Boron sorption on two calcareous soils, one noncalcareous soil, and two reference calcites was investigated in batch systems both as a function of solution pH (5.5–12) and as a function of initial B concentration (1–250 g B m−3). Boron sorption was investigated on untreated soil samples, and soil samples treated with dilute acid to remove soil calcite. Boron sorption on the soil samples increased from pH 5.5 to 9, exhibited a peak near pH 9.5, and decreased from pH 10 to 11.5. Boron sorption on the two reference calcites exhibited an adsorption envelope with maximum sorption occurring near pH 9.5. The magnitude of the B adsorption maximum was significantly lower for the soil samples treated for calcite removal than for the untreated soil samples. This result indicates that calcite plays an important role in B sorption by calcareous soils. Boron sorption as a function of equilibrium B concentration could be described by both the Freundlich and Langmuir adsorption isotherms over the entire concentration range studied on all materials. Goodness of fit of the Langmuir adsorption isotherm equation was much improved over linear transformations by using the program ISOTHERM with its nonlinear least squares optimization routine.

Influence Of Anion Competition On Boron Adsorption By Clays And Soils

Boron adsorption on the clay minerals, kaolinite and montmorillonite, and two arid zone soils was investigated as a function of solution pH (3-12) and presence of competing anions (nitrate, sulfate, molybdate, and phosphate) after 2 h of reaction time. Boron adsorption on all materials increased from pH 3 to 8, exhibited a peak at pH 8 to 10, and decreased from pH 10 to 12. Boron adsorption was greatest using a NaNOJ background electrolyte. The competitive anion effects on B adsorption increased in the order sulfate < molybdate < phosphate. The competitive effect on B adsorption was small even for the strongly adsorbing anion, phosphate. Our results suggest that B-adsorbing sites are, generally, specific to B and act independently of competing anions. This result will simplify the description of B transport in that changes in solution concentration of competing anions may not have to be considered.

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

Management options for reducing drainage water volumes on the west side of the San Joaquin Valley of California, such as reuse of saline drainage water and water table control, have the potential to adversely impact crop yields due to a build up in soil solution boron concentration. An earlier experiment had shown that extrapolation of B soil tests to field conditions provided poor predictability of B content of melons despite statistically significant relationships. Consequently, three tests for extractable soil B were evaluated for their ability to predict conditions of potential B toxicity in melons grown under controlled conditions. Melons were grown for 95 days in two consecutive years in containers of Lillis soil (very-fine, smectitic, thermic Halic Haploxerert) that had been pretreated with solutions containing B concentrations as great as 5.3 mmol L−1. Extractable soil B was determined using ammonium acetate, DTPA-sorbitol, and a 1:1 aqueous soil extract at the beginning and end of the experiment. The B treatments caused various deleterious effects on melon growth and development. Fresh and dry plant matter decreased significantly with increasing B concentrations, while B concentration of plant leaves, stems, and fruits increased significantly with increasing B. The number of days to first flowering was significantly delayed from 35 days at B treatments < 2 mmol L−1 to 51 days at B treatments > 3 mmol L−1. Fruit set was completely inhibited at the highest B treatment of 5.3 mmol L−1. Plant analysis revealed a highly significant relationship between soil extract B obtained with all three extractants and leaf, stem, and fruit B content. Correlation coefficients for plant stems and fruits were much higher than for plant leaves. Correlation coefficients for all soil tests were almost equivalent, although the highest values were obtained for the DTPA-sorbitol extract indicating the greatest predictive capability. The soil tests were well able to predict B damage to melons in a container experiment.

Temperature effects on boron adsorption by reference minerals and soils

Information on the effect of temperature on B adsorption by soils and soil minerals is scant. These data are needed to understand B availability. Boron adsorption on goethite, gibbsite, kaolinite, montmorillonite, calcite, and two arid zone soils was investigated as a function of solution pH (3–12) and reaction temperature (10, 25, and 40|MoC) after 2 h of reaction time. Boron adsorption on all materials increased from pH 3 to 7, exhibited a peak at pH 7.5 to 10, and decreased from pH 10.5 to 12. Temperature dependence measured as the increase of the B adsorption maximum at 10|MoC compared with 40|MoC on reference minerals increased in the order: calcite (3|X%) < goethite (7|X%) < gibbsite (18|X%) < montmorillonite (-20|X%) < kaolinite (26|X%). The kaolinitic soil exhibited greater temperature dependence than the smectitic soil. The B adsorption reaction was exothermic since B adsorption decreased with increasing temperature for all materials, except for montmorillonite at high pH. Highly specific ion adsorption is expected to be exothermic, suggesting an inner-sphere adsorption mechanism for B on all reference minerals except montmorillonite.

FLOCCULATION OF ILLITE/KAOLINITE AND ILLITE/MONTMORILLONITE MIXTURES AS AFFECTED BY SODIUM ADSORPTION RATIO AND pH

The effect of electrolyte concentration, exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and pH on the flocculation-dispersion behavior of 50/50 mixtures of reference illite with reference kaolinite or reference montmorillonite was investigated. The clays were Na- or Ca-saturated and freeze-dried before use. Critical coagulation concentrations (CCCs) were investigated in the range of pH 5.9 to 9.6, percent Na-clay 0, 10, 20, 40, 60, 80, and 100 and SAR 0, 10, 20, 40, 60, 80, and ∞. CCC values increased with increasing ESP, increasing SAR, and increasing pH. The pH dependence of illite/kaolinite was greater than that of illite/montmorillonite especially at high ESP and SAR. The presence of illite did not play a dominant role in determining flocculation-dispersion behavior of the 50/50 clay mixtures. The CCCs of illite/kaolinite resembled reference illite more than reference kaolinite for SAR 0 to SAR 60. Illite/montmorillonite exhibited CCCs more similar to reference illite than reference montmorillonite at SAR 40 and SAR 60. At the agriculturally desirable ESP and SAR values of 0 to 15, all the 2:1 clays and 2:1 clay mixtures demonstrated similar CCC values.

Soil boron extractions as indicators of boron content of field-grown crops

Determining the relationship between soil B and crop B content can help predict when crops will respond to B fertilizer and when B toxicity may be expected. Such a relationship can then be used to make fertilizer recommendations or to flag conditions of potential B toxicity. Soil samples were obtained from 65 sites located in the Broadview Water District in the San Joaquin Valley of California. A diverse set of extractants was evaluated including: hot water-soluble, 1:1 soil:distilled water and 1:2 soil:distilled water, ammonium acetate, calcium chloride-mannitol, and DTPA-sorbitol extracts. Soil extract B values were correlated significantly with various B reactive soil constituents, including aluminum and iron oxide, clay, organic matter, and calcium carbonate content. The 1:1 water extract B was highly significantly correlated (99% level) with other measures of extractable B used in the study. Extractants were compared on soil samples collected from six depths at 65 field sites in the San Joaquin Valley of California that were cropped to alfalfa, melons, and cotton. Boron concentrations of whole plants and composites of 10 leaves were determined. Plant sampling occurred at the time of soil sampling for the alfalfa. Cotton and melons were sampled at flowering and prior to fruit set, the recommended growth stages, respectively, for tissue sampling, and 6 weeks thereafter. Five weeks later the cotton was sampled a third time. Significant correlations (95% level) between extractable soil B and plant B were found for melons and cotton but not for alfalfa. Correlation coefficients for the ammonium acetate, DTPA-sorbitol, and 1:1 water extract were not statistically significantly different (95% level). Although significant correlations (95% level) were obtained, the equations provided relatively poor predictive capability. These results illustrate the difficulty of predicting plant B content based on soil B analyses from a single soil sampling.