Trace element availability to plants in agricultural soils, with special emphasis on fertilizer inputs

Abstract

Fertilizers, along with atmospheric deposition, are believed to contribute more than all other factors to the trace element burden of cultivated soils. This review will discuss trace elements in commercial fertilizer in relation to their transfer to soil–plant systems. Also, background levels in soils and the concentrations of trace elements in soils, phosphate rocks, and commercial fertilizers will be presented. Results from several short and long-term experiments indicated that the application of phosphate fertilizers to agricultural soils generally resulted in an increase of trace elements in soils and that the increase was most pronounced for Cd. The corresponding increase in plants was quite variable, ranging from no increase at all to a significant increase. The concentration of trace elements in plant species also showed a wide variation. The distribution and partitioning of trace elements among chemical associations in soils varied considerably for different elements. The highest percentage of Cd in soils, as estimated by sequential extraction, was associated with exchangeable fractions (25–41%), but the highest fraction of Zn (47%) was associated with resistant minerals. Uptake of trace elements by plants and solubility and mobility of these elements in the soil were affected to a greater extent by the plant species grown and soil pH, organic matter, and soil texture. Soil pH showed a significant but inverse relationship with the concentrations of most of the trace elements in plants. The addition of organic matter generally immobilized the trace elements in soils and caused reduction in plant uptake of most elements. A considerable proportion (up to 50%) of the total uptake of trace elements, and especially of Cd, was a result of atmospheric deposition. Ecological implications of contaminants in fertilizers and the resultant need for research are described.Key words: accumulation in soils, fertilizers, plant availability, soil properties, trace elements.