Mitigating decomposition in agricultural peatlands: Influence of copper and polyphenol on C N P dynamics and enzyme activities in two contrasting soils

Abstract

Drained agricultural peatlands are subject to degradation through decomposition, compaction, and erosion. This study aimed to (1) revisit an existing recommendation to systematically apply copper at a rate exceeding crop needs to slow the decomposition of agricultural peatlands, and (2) explore lignosulfonate, a polyphenol, as an alternative method to copper. Two peat soils with contrasting levels of humification (sapric and hemic) and differing Al and Fe contents were studied under controlled conditions. CO2 emissions cumulated in the two unamended soils differed importantly, representing 0.7 and 7.3 t C-CO2 ha−1 yr−1 (0–25 cm) in the sapric and hemic soil, respectively. In the sapric soil, copper did not affect CO2 emissions, N and P parameters, or the activity of most of the measured enzymes. In the same soil, lignosulfonate increased CO2 emissions and phenol oxidase activity, suggesting that the product acted as a microbial substrate. In the hemic soil, copper and lignosulfonate reduced cumulated CO2 emissions by 37 % and 61 %, respectively, as well as N parameters and phosphatase activity. The influence of both treatments on CO2 emissions was, however, temporary. This study suggests limited efficiency of copper and lignosulfonate when applied to soils where underlying mechanisms, such as organic matter recalcitrance and Al and Fe stabilization effect, already regulate decomposition rates. The divergent and temporary effects of copper found in this study and in the literature suggest that routine applications of copper at a rate exceeding crop needs is not consistently effective in slowing decomposition in agricultural peatlands. Lignosulfonate appears to be a promising alternative to copper. The inhibitory effect of polyphenol applications has been demonstrated in natural peatlands but, to our knowledge, this is the first time it has been reported for drained agricultural peatlands. Evaluating the influence of lignosulfonate on other drained agricultural peat soils and under field conditions is necessary to determine the potential of this approach.