The effects of applied crop residues on losses of Fe, Mn, Cu and Zn in run‐off from a soil prone to crusting

Abstract

AbstractTillage practices may reduce the organic matter content in near‐surface soil horizons causing crust formation. Surface conditions may cause an increase in surface run‐off, thus enhancing contaminant transfer of heavy metals or an acceleration in nutrient loss. This study examines the effect of applying crop residues to the surface of tilled soils on heavy metal losses by run‐off. Losses in iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were analysed. Run‐off and sediment yield were measured on 1 m2 plots using a rainfall simulator with a constant 65 mm/h intensity. Four successive rainfall applications were performed, the first three at 25 mm each and the last at 65 mm. Added corn straw varied between 0 and 4 t/ha in the five studied treatments. After 140 mm cumulative rainfall, total heavy metal losses were as follows: Fe from 137 to 950 mg/L, Mn from 2.3 to 12.83 mg/L, Cu from 0.09 to 0.72 mg/L and Zn from 0.31 to 2.46 mg/L. Dissolved fractions were as follows: Fe from 0.014 to 0.229 mg/L, Mn from 0.034 to 1.45 mg/L, Cu from 0.002 to 0.013 mg/L and Zn from 0.02 to 0.12 mg/L. Total concentrations of the studied elements decreased exponentially due to the effect of corn straw on soil loss. However, dissolved contents of Fe and Cu scarcely varied. Significant positive linear correlations were observed between total heavy metal content and soil and sediment loss by run‐off. It is concluded that the addition of straw to a soil of low fertility prevents heavy metal loss.