Accumulation of cadmium, fluorine, magnesium, and zinc in soil after application of phosphate fertilizer for 31 years in a grazing trial
2010
McGrath, Dave | Tunney, Hubert
Phosphate fertilizers are recognized as a potential source of elements that could contribute to soil pollution. The objective of this study was to determine the extent to which use of phosphate fertilizer in the past had resulted in an increase in heavy-metal content in Irish soils. Samples were taken from a long-term replicated (six replicates of 0.18 ha each) plot experiment with grazing cattle. Phosphate as superphosphate had been applied at two rates, 0 and 930 kg ha⁻¹ total P, over a 31 y period. Phosphorus, pH, soil organic matter, Cd, F, Mg, and Zn were measured in 0-10 and 10-20 cm soil layers in addition to extractable P and Mg (Morgan's solution) and Zn (0.5M EDTA). Increases in the phosphate-enriched soil were significant at p < 0.05 except for F at both soil layers and for Cd at the 10-20 cm layer (p < 0.1) Recoveries for P, Cd, and F were in fair agreement with application. High recoveries of total Mg and Zn were encountered which could not readily be explained. These increases were paralleled by increases in extractable-soil-test values for these elements. Accumulation in soil of P over the period was such as to now necessitate little application of this element to soil for the near future. At the same time, increase in soil Cd was small, little more than 0.05 mg kg⁻¹ in soil, although it amounted to a sizable proportion of Cd in the soil. Similarly, increases in other elements, although real, would not lead to major concerns at the present time.
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