Phosphorus deficiency is the major limiting factor for wheat on alluvium polluted by the copper mine pyrite tailings: a black box approach

Abstract

Failures of tailings dams have degraded large areas of agricultural alluvial soils worldwide, and concomitant soil pollution studies are abundant. Yet, the data on the actual effects of thereby imposed stresses on major crops are scarce. This work analyses the effect of pyrite tailings from a copper mine, deposited over crop fields by long-term flooding, on wheat (Triticum aestivum L.) under field conditions. The major previously reported polluting agents were Cu, As, Zn, Pb and acidity generated by sulphide oxidation. Flexible systematic sampling, based on visual symptoms in wheat, included transects through partially damaged fields (from calcareous to acid soils). Multivariate analysis of soil properties, leaf mineral composition and growth parameters revealed a consistent underlying soil gradient of decreasing available P and increasing S-tot. Phosphorus was shown to have the highest unique contribution to predicting wheat yield, consistent correlation with growth and visual symptoms, and concentrations in the range of severe deficiency. In P deficient plants N deficiency, decrease of available micronutrients and increase of As occur irrespectively of their soil concentrations, and the competition with superior "pyrite" weeds increases. Different sorption of P and possible rhizotoxic effects of other pollutants imply that fertilization can hardly be a solution.