Review of Impacts on Soil Biota Caused by Copper Residues from Fungicide Application

Abstract

Unlike most other agricultural chemicals, copper-based fungicides have a long-term impact on a wide range of soil biota. Effects can occur at relatively low Cu concentrations and influence soil processes including microbial activity, earthworm activity, and bioturbation. Copper residues are likely to remain in most soils indefinitely, influencing soil health. This manuscript reviews Australian and international data on the effects of copper fungicides on soil health and their implications for future land management.

Key words

Copper fungicide, earthworm avoidance, microbial activity.

Introduction

The use of pesticides has long been a feature of conventional agricultural practice, contributing to increased crop yields and food production. However, many chemicals have toxic effects that extend beyond their target species, impacting organisms that benefit the wider agroecosystem. The uncertainty in predicting the impacts of external stressors like pesticide application on agricultural ecosystems is considerable (Liess, 2004). Questions have arisen over the significance of changes in soil organism populations, especially when no other indicator of harm is documented. The diversity of soil organisms, including bacteria, fungi, yeasts, nematodes, mites, insects, and earthworms, contributes to soil functions like nutrient storage, residue decomposition, and soil structure stability.

Copper Fungicides and Their Use in Australia

The discovery of the Bordeaux mixture in the 1880s led to the rapid development of copper fungicides. Copper-based fungicides have been widely used for over 100 years in Australian horticulture, particularly in pome and stone fruit orchards, vineyards, and vegetable crops. Over 7500 tons of Cu fungicides are used annually in Australia, which is 13% of the global total (Lepp & Dickinson, 1994). However, the accumulation of copper in soils, particularly in regions with long histories of fungicide application, has raised concerns about their impact on soil biota and long-term soil health.

Impacts of Copper on Soil Biota

Recent studies in Australia show that copper residues in avocado orchards significantly impact soil microorganisms. In a study of avocado orchard soils in northern NSW, the copper concentration was found to be much higher than that in a nearby reference site under natural vegetation. The higher copper levels were associated with significant reductions in microbial biomass, soil respiration, and other soil health indicators such as the microbial biomass to organic carbon ratio (Merrington et al., 2002).

Earthworm Avoidance Studies

Earthworm populations are sensitive indicators of soil health. Avoidance studies conducted on avocado orchard soils with high copper levels showed that earthworms preferred non-contaminated soils. At copper concentrations of 553 mg/kg, 90% of earthworms avoided the copper-contaminated orchard soil, reflecting the toxic impact of copper on these organisms (Van Zwieten et al., 2004).

Discussion

Copper is an essential element, but elevated levels in soil can be toxic and result in reduced biological activity, which may decrease soil fertility. Studies in Australian avocado orchards have shown that copper residues affect microbial activity, earthworm populations, and other soil processes such as bioturbation. Earthworms, vital to soil health due to their role in decomposition, aeration, and nutrient cycling, have been shown to avoid copper-contaminated soils, further confirming the detrimental effects of copper residues.

Conclusions

The evidence reviewed demonstrates that copper residues from fungicide application reduce soil microbial biomass and stress the microorganisms that remain. This has a negative impact on soil processes like bioturbation, which is crucial for soil structure and function. Further research is needed to evaluate the long-term effects of copper contamination and to develop management strategies and remediation technologies to reduce copper bioavailability in soils. Reducing the use of copper fungicides, exploring alternative control agents, and improving soil management practices are essential steps in mitigating the environmental impact of copper residues in agricultural soils.

References

• Alva AK, Huang B, Paramasivam S. (2000). "Soil pH affects copper fractionation and phytotoxicity." Soil Science Society of America Journal, 64, 955-962.
• Böckl M, Blay K, Fischer K, Mommertz S, Filser J. (1998). "Colonisation of a copper-decontaminated soil by micro- and mesofauna." Applied Soil Ecology, 9, 489-494.
• Gallagher DL, Johnston KM, Dietrich AM. (2001). "Fate and transport of copper-based crop protectants in plasticulture runoff and the impact of sedimentation." Water Research, 35, 2984-2994.
• Lee KE. (1985). "Earthworms: Their Ecology and Relationships with Soils and Land Use." Academic Press, Australia.
• Merrington G, Rogers SL, Van Zwieten L. (2002). "The potential impact of long-term copper fungicide usage on soil microbial biomass and microbial activity in an avocado orchard." Australian Journal of Soil Research, 40, 749-759.
• Van Zwieten L, Rust J, Kingston T, Merrington G, Morris S. (2004). "Influence of copper fungicide residues on occurrence of earthworms in avocado orchard soils." The Science of the Total Environment, 329, 29-41.
• Van Zwieten M, Stovold G, Van Zwieten L. (2004b). "Literature Review and Inventory of Alternatives to Copper for Disease Control in the Australian Organic Industry." RIRDC Project DAN-208A.