Plant Availability and Uptake of Molybdenum as Influenced by Soil Type and Competing Ions

Abstract

Irrigation has been proposed as a possible disposal method for large quantities of water having high concentrations of Mo (5-100 mg -1) resulting from mining and reclamation activities. To assess this possibility, laboratory and greenhouse experiments were conducted to evaluate the influence of competing ions in the soil solution on the relationship between the sorption of Mo by soils and Mo uptake by grass. Laboratory experiments assessed Mo sorption by Edroy clay (Vertic Haplaquoll), Olmos loamy sand (Petrocaicic Calciustoll), and Randado sandy loam (Ustoilic Paleargid). Soil treatments included 1, 5, 10, 20, 50, and 100 mg Mo L -1 added as ammonium molybdate in solutions of 0, 167, 333, and 500 mg L -1 concentrations of CI-and 0, 226, 451, and 677 mg L -t concentrations of SOl" salts. Sorption data fit the Freundlich isotherm. The Olmos soil had the highest CaCO3 content and sorbed the most Mo. The Edroy soil had the lowest pH and sorbed the least Mo. The presence of Ci-in solution increased Mo sorption, while SOl-reduced Mo sorption in all three soils. In the greenhouse study, soils were treated with 0, 6.5, 13.0, and 26.0 mg Mo kg -t soil; 167, 334, and 501 mg CI kg -~ soil; and cropped with bermudagrass, Cynodon dactyion (L.) Pets. No toxic symptoms or yield decreases were noted as a result of Mo or salt additions. Plants grown in soil containing 26.0 mg Mo kg -~ accumulated up to 600 mg Mo kg -~ dry matter and would be toxic to ruminants. The Mo concentrations in grass grown on the three soils were ranked from highest to lowest as Edroy > Randado > Olmos. Chloride addition to the soil had no significant (P <0.05) effect bermudagrass Mo content. Both the concentration of Mo in the vegetation and the amount of Mo taken up by the vegetative cover were well correlated (r~ = 0.73 and 0.83, respectively) with the equilibrium solution Mo in the soil as calculated from the sorption isotherms. Thus, the results indicate that there is a strong relationship between the laboratory sorption data and the equilibrium solution Mo in the soil and that grass grown on soil irrigated with waters high in Mo may reach levels that are expected to be toxic to animals. Additional index words: Freundilch isotherm, Chloride, Sulfate, Bermudagrass, Cynodon dactylon (L.) Pets.

Competitive Adsorption of Molybdenum in the Presence of Phosphorus or Sulfur on Gibbsite

“…At a 1:140 molar ratio of Mo/P, reductions in Mo adsorption were observed; whereas at a 1:240 molar ratio of Mo/S, no effect of S on Mo adsorption was noted. The lack of competitive effect of the presence of sulfate in the study of Gorlach et al (1969) was not caused by differences in Fe or Al oxide content or organic matter content because their soils were intermediate in these properties between those of Smith et al (1987) and Xie and MacKenzie (1991).…”

“…Reductions in Mo adsorption were observed in all of the phosphate studies and some of the sulfate studies (Brinton and O'Connor, 2000;Smith et al, 1987). Only in the study of Gorlach et al (1969) were Mo, S, and P added in proportions realistic for soils.…”

“…Recognizing that phosphate and sulfate occur at higher concentrations than Mo in nature, studies on soils have been conducted at Mo/P molar ratios of 1:5 (Brinton and O'Connor, 2000), 1:9 (Xie and MacKenzie, 1991), and 1:10 (Gonzalez et al, 1974) and at Mo/S molar ratios of 1:5 (Brinton and O'Connor, 2000), 1:6 (Smith et al, 1987), and 1:10 (Gonzalez et al, 1974). Reductions in Mo adsorption were observed in all of the phosphate studies and some of the sulfate studies (Brinton and O'Connor, 2000;Smith et al, 1987).…”

Sorption Of Molybdenum In Soils Field-equilibrated With Biosolids

“…[5] Phosphate solutions can displace adsorbed Mo from soil [16] and sulfate can also reduce the amount of Mo sorbed on soils. [17] To investigate whether there was sufficient sulfate and phosphorus in the field systems to produce competition, phosphorus and sulfate concentrations were determined on selected fieldequilibrated samples (Year 2 Millhopper and Year 3 Immokalee samples only). We hypothesized that sufficient sulfate and phosphorus in the system might explain the reduced Mo sorption by biosolids-amended soils as compared to native soils not attributable to pH effects (Figs.…”

Aperfeiçoamento de procedimento analítico para a determinação de molibdênio disponível em solo e fertilizante orgânico.

“…Quando aplicado ao solo em doses excessivas, este microelemento pode ser causa de toxicidade, uma vez que 10 mg de Mo kg -1 de matéria seca vegetal pode gerar molibdenose em ruminantes (SMITH et al, 1987).…”