Engineered/designer biochar for contaminant removal/immobilization from soil and water: Potential and implication of biochar modification

The essential micronutrients for field crops are B, Cu, Fe, Mn, Mo, and Zn. Other mineral nutrients at low concentrations considered essential to growth of some plants are Ni and Co. The incidence of micronutrient deficiencies in crops has increased markedly in recent years due to intensive cropping, loss of top soil by erosion, losses of micronutrients through leaching, liming of acid soils, decreased proportions of farmyard manure compared to chemical fertilizers, increased purity of chemical fertilizers, and use of marginal lands for crop production. Micronutrient deficiency problems are also aggravated by the high demand of modern crop cultivars. Increases in crop yields from application of micronutrients have been reported in many parts of the world. Factors such as pH, redox potential, biological activity, SOM, cation-exchange capacity, and clay contents are important in determining the availability of micronutrients in soils. Plant factors such as root and root hair morphology (length, density, surface area), root-induced changes (secretion of H + , OH − , HCO 3 − ), root exudation of organic acids (citric, malic, tartaric, oxalic, phenolic), sugars, and nonproteinogenic amino acids (phytosiderophores), secretion of enzymes (phosphatases), plant demand, plant species/cultivars, and microbial associations (enhanced CO 2 production, rhizobia, mycorrhizae, rhizobacteria) have profound influences on plant ability to absorb and utilize micronutrients from soil. The objectives of this article are to report advances in research on the micronutrient availability and requirements for crops, in correcting deficiencies and toxicities in soils and plants, and in increasing the ability of plants to acquire needed amounts of micronutrient elements.

Micronutrients in Crop Production

A review on the potentiality of Rare Earth Elements to trace pedogenetic processes

Phosphate adsorption using modified iron oxide-based sorbents in lake water: Kinetics, equilibrium, and column tests

Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review

Molybdenum adsorption behavior was investigated on various crystalline and x-ray amorphous Al and Fe oxide minerals, clay minerals, CaC@, and arid-zone calcareous and noncalcareou s ssoils. Molybdenum adsorption on botb Al and Fe oxides exhibited a maximum at low pH extending to about pH 4 to 5. Above pH 5 adsorption decreased rapidly, with little adsorptio noccurring above pH 8. Molybdenum adsorption was higher for the oxide minerals having higher specific surface area and lower crystallinity. Molybdenum adsorption on the clay minerals exhibited a peak near pH 3 and then decreased rapidly with increasing pH until adsorption was virtually zero near pH 7. The magnitude of MO adsorption on clays increased in the order: kaolinite < illite < montmorillonite. Shifts in point of zero charge were observed on Al and Fe oxides and kaolinite following MO adsorption, indicating an inner-sphere adsorption mechanism for MO on these surfaces. Molybdenum adsorption behavior on three arid-zone noncalcareous soils resembled that on clays, exhibiting a peak near pH 3 to 4 and decreasing with increasing pH up to pH 7. This behavior is expected since the oxide content of these soils is low. Molybdenum adsorption on calcite and tw ocalcareous arid-zone soils was low, indicating that CaCOJ is not a significant sink for MO in soils.

C.L. Godfrey

Papers

Molybdenum Adsorption on Oxides, Clay Minerals, and Soils