Copper is an essential micronutrient for plant growth and health. While required in small amounts, copper plays important roles in plants including photosynthesis, respiration, metabolism, and the formation of lignin that provides structural support. Copper deficiency can stunt growth, cause wilting or dieback, and lead to reduced yields. Providing adequate copper nutrition ensures plants have access to this critical nutrient. There are several effective options for supplying copper fertilizer to meet the nutritional needs of plants.
Copper sulfate is one of the most widely used copper fertilizers. This inorganic salt contains 25% copper. It readily dissolves in water, making the copper available for rapid root uptake and translocation within the plant. Copper sulfate can be applied directly to soil as a powder or crystalline form. It is also easy to apply through irrigation systems by injecting a solution. Rates vary based on soil properties and desired concentrations in tissues but often range from 2 to 10 pounds per acre for field crops.
Copper sulfate provides readily bioavailable copper but can be lost through leaching. It may need to be reapplied periodically to maintain adequate levels, especially on sandy soils. Potential drawbacks include phytotoxicity if over-applied and negative impacts to soil microbes at high levels. Care should be taken to apply copper sulfate at recommended rates.
Copper oxide is another inorganic source of copper fertilizer. Two forms are used – CuO and Cu2O – containing 80% and 88% copper respectively. The release of copper from these oxides is dependent on pH. As soils become more acidic, higher amounts of copper are solubilized. Copper oxide tends to provide a slower, steadier supply of copper over an extended period of time compared to copper sulfate.
Copper oxide can be blended into granular fertilizers or impregnated onto fertilizer granules. Broadcast application provides copper nutrition. Impregnated granules release copper as they slowly dissolve. This provides the advantage of placing immobile copper in the root zone for uptake as the roots grow. Recommended application rates are 2 to 15 pounds per acre.
Chelated Copper Products
Chelated copper products contain copper bound to organic molecules. This helps keep the copper stable and available in the soil instead of binding tightly to minerals. There are a variety of chelating agents used such as EDTA, HEDTA, EDDS, and amino acids. These form soluble, stable complexes that are readily taken up by plant roots.
Chelated copper provides effective foliar or soil nutrition. It is useful for deficient soils, high pH soils that tie up copper, and foliar treatments when a rapid response is needed. Chelated products are also less prone to phytotoxicity issues. Rates vary from 0.5 to 2 pounds per acre for field applications. Chelated copper products are often used in hydroponic systems as well.
Organic Copper Amendments
There are several options for incorporating copper into soils through organic amendments. These include:
- Compost – Well-made compost contains trace levels of many micronutrients. Quality compost provides 2-10 ppm copper.
- Manure – Manure derived from livestock feeding contains residual undigested copper. Rates of 15-25 ppm are typical.
- Green manures – Growing legumes and plowing under the residue recycles copper removed from the soil.
- Seaweed extracts – Derived from brown seaweed like kelp, these fertilizers contain numerous micronutrients including copper.
- Fish fertilizers – Fish emulsion can provide micronutrients in plant-available forms.
These organic amendments not only supply copper but also improve soil quality. Their benefit extends beyond just the addition of copper for balanced plant nutrition.
Diagnosing Copper Deficiency
Routine soil tests help monitor levels of plant-available copper. Soil testing every 2-3 years monitors copper status and determines if supplementation is needed. More frequent tissue testing reveals if plants are taking up adequate copper over the growing season.
Visual symptoms can also indicate copper deficiency. These include:
- Stunted growth.
- Wilting, dieback, or chlorosis.
- Lack of fruit set or poor yields.
- Discolored spots on leaves.
Correcting deficiency requires 2-5 pounds of copper per acre depending on original levels. Chelated forms or several smaller applications provide flexibility.
Balancing Copper Nutrition
Adequate copper supply supports plant growth, yield, and quality. However, excessive levels can create toxicity. It is important to apply copper fertilizers judiciously, follow label rates, and retest regularly. This maintains the balance between deficiency and excess. Chelated forms are recommended for ease of application and low toxicity risk. Consult local extension resources to tailor copper fertility programs to specific soils and crops. With proper copper management, plants have access to this critical micronutrient.
Impacts on Soil Microbes
While copper is an essential plant nutrient, it can act as a bacteriocide and fungicide at higher concentrations. Excess copper impacts populations of beneficial soil microbes such as nitrogen-fixing bacteria and mycorrhizal fungi. This effect on soil biology may temporarily depress nutrient cycling and availability.
Copper builds up over time since it is not broken down. Monitoring application rates helps prevent long-term microbial impacts. Using more bioavailable forms like chelated copper minimizes toxicity effects on soil microbes. Allowing periods between applications, such as alternating years, gives microbes time to repopulate.
Copper Toxicity in Plants
While copper is an essential plant micronutrient, excess amounts can cause copper toxicity. This occurs when copper accumulation exceeds the plant’s threshold, impairing growth and health. Toxicity symptoms include stunted roots and shoots, chlorosis, necrosis, and leaf discoloration. In susceptible species, excess copper also causes injury to plasma membranes, altering permeability. This leads to metabolic disorders and interference with nutrient transport and photosynthesis.
Copper toxicity depends on soil factors, application rates, and crop sensitivity. Acidic, organic, and sandy soils increase bioavailability and toxicity risks. Excessive fertilizer application or use of unchelated forms raises levels beyond optimal ranges. Certain fruits, vegetables, and ornamentals have lower copper tolerance. Monitoring soil and tissue levels along with controlled fertilizer inputs prevents toxic accumulation. Allowing adequate time between applications provides margins of safety. With proper management, copper fertility promotes plant health without surpassing toxicity thresholds.
Advances in fertilizer technology will provide more options for copper nutrition. Polymer coatings can control copper release rate from granules. Biodegradable chelates reduce persistence in the environment. Nanoparticles increase uptake efficiency and effectiveness. And plant breeding selects for efficient copper use within crops. These innovations will fine-tune delivery of this essential mineral.
The key to any fertilization program is applying the right source at the proper rate and timing for each situation. Understanding copper dynamics in soil and plants along with strategic testing enables this balance. With informed management, copper fertilization supports plant productivity and health. This essential nutrient plays pivotal roles across all aspects of plant development.