Does Different Types of Manure Application Influence the Soil Trace Metal Contents?.

This project was initiated to study, under the same soil and climatic conditions, the fertilizer value of pig slurry, cattle slurry and poultry manure as well as the associated environmental risks. In this particular study, we evaluated the impact of repeated application of various manure types on the availability of trace metals. Two fields (silty clay; sandy loam) were divided into 60 plots according to a split-split-plot design with three replicates near Québec City, eastern Canada. The main plots consisted of tillage: no-till vs. plowing. The sub-plots were the fertilizer treatments: control, mineral fertilization, pig slurry, cattle slurry and poultry manure. The sub-sub-plots involved residue management: left in the field or removed. Soils were sampled annually from 2009 to 2016 to monitor total and available forms of trace metal (Cu, Mn, Zn). The mean concentration of total Cu, Mn, and Zn was 12, 186, and 54 mg kg-1 after 5 yr of repeated application of pig, cattle and poultry manure, respectively. This resulted in increases of 25, 15 and 11%, respectively, compared to the beginning of the study. Total concentrations of Cu, Mn, and Zn in the silty clay were higher in the cattle slurry and the poultry manure treatments, when the residues were removed from the plots either under no-till or plowing. The reverse was observed for the pig slurry treatment in the no-till plots. Similar results were found in the sandy loam, but the effects were less pronounced. Crop residues returned to the soil may have acted as an adsorbent for metals since the concentrations in soil were lower compared soils where residues were removed. Similar results were observed with available forms of metals. Globally, leaving crop residues in the field appears to lower metal accumulation in soils, especially in clayey soils. These results highlight how management practices may interact and influence the accumulation and availability of trace metals in soils with repeated application of livestock manure.