Abstract
Copper-based fungicides have been used for a long time in viticulture and have accumulated in many vineyard soils. In this study, incrementing Cu(OH)2-based fungicide application from 0.05 to 5 g Cu kg−1 on two agricultural soils (an acidic sandy loam (L, pH 4.95) and an alkaline silt loam (D, pH 7.45)) resulted in 5 times more mobile Cu in the acidic soil. The most sensitive parameters of alfalfa (Medicago sativa) growing in these soils were the root nodule number, decreasing to 34% and 15% of the control at 0.1 g Cu kg−1 in soil L and at 1.5 g Cu kg−1 in soil D, respectively, as well as the nodule biomass, decreasing to 25% and 27% at 0.5 g Cu kg−1 in soil L and at 1.5 g Cu kg−1 in soil D, respectively. However, the enzymatic N2-fixation was not directly affected by Cu in spite of the presence of Cu in the meristem and the zone of effective N2-fixation, as illustrated by chemical imaging. The strongly different responses observed in the two tested soils reflect the higher buffering capacity of the alkaline silt loam and showed that Cu mitigation and remediation strategies should especially target vineyards with acidic, sandy soils.
Highlights
Supplementary information The online version of this article contains supplementary material, which is available to authorized users.Salts of Cu are used in agriculture since more than 120 years.Either CuSO4 or more recently Cu(OH)2 show superior fungicidal properties and a lack of resistances of fungi, compared to synthetic fungicides (Kühne et al 2009)
The ethylenediaminetetraacetic acid- (EDTA)-Cu and CDGT-Cu concentrations were consistently increasing along application rates with the first significant increase at 1.5 g kg−1
This work reported plant responses in soil after application of a Cu-based fungicide at moderate to very high concentrations, with the highest treatment being more strongly contaminated than former vineyards (Bravin et al 2010; Michaud et al 2007)
Summary
Either CuSO4 or more recently Cu(OH) show superior fungicidal properties and a lack of resistances of fungi, compared to synthetic fungicides (Kühne et al 2009). Their preventive applications mitigate losses in photosynthetically active leaf area in vineyards, mainly caused by the infection with downy mildew (Plasmopara viticola). Current maximum application rates of 3 kg Cu ha−1 on conventionally grown grapevine in Austria, or 6 kg Cu ha−1 according to EU-legislation (EC 2008) are not supposed to cause remarkable increases in soil Cu contents, compared to inputs through sewage sludge or manure. The majority of contaminations on agricultural soil was caused by application rates of 30 and even up to 80 kg Cu ha−1 before 1970 (Kühne et al 2009). Soils may show Cu accumulation due to low harvest withdrawals of 3–30 mg kg−1 plant dry weight (dw) (Amelung et al 2018) and because of longterm use of Cu-based fungicides, which is nowadays, especially in organic farming systems, still inevitable
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