Effect of long-term swine-manure application on soil hydraulic properties and heavy metal behaviour

Abstract

This study evaluated the effect of 13 years of swine-manure application on the changes in soil hydraulic properties, and as associated physicochemical properties, with a focus on heavy metal mobility. Various soil hydraulic properties were measured, including soil water retention (SWR), saturated field hydraulic conductivity (K fs) and unsaturated field hydraulic conductivity (K funsat) using a disc infiltrometer. Heavy metal mobility was evaluated with a sequential extraction procedure. At 0-30 cm soil depth in the heavily manured plot (SMhigh plot), SWR at 0 to -100 kPa was significantly larger than in plots amended with a standard amount of manure (SMstd plot) or with chemical fertilizer (CF plot). K fs and K funsat values in both manure-amended plots were less than in the CF plot under dry soil conditions but greater than those of the CF plot under wet soil conditions. Furthermore, K fs and K funsat did not necessarily increase with manure application rates. On the other hand, high-mobility metal fractions, such as the exchangeable fraction of Zn, and the CH 3CO 2Na-extractable fraction of Zn and Mn, and the metal-organic complex fractions of Zn, Cu and Mn, increased with the greater manure application rate. In addition, low-mobility metal fractions, the organically bound fractions of Zn, Cu and Mn in the high SM plot and the easily reducible metal oxide fraction of Mn in both manure-amended plots were probably affected and released into high-mobility fractions. This indicated that manure application changed the soil redox conditions by improving the soil structure, depending on the water content of soil pores. Despite the reduction of K fs and K funsat by heavy manure application, the transport of high-mobility metal fractions with either surface water flow or infiltration water flow could be controlled by soil water content at the beginning of a rain or irrigation event. © 2012 The Authors. Journal compilation © 2012 British Society of Soil Science.