Organic soils often contain plenty of copper, but is it in a form that’s actually available to plants? Maintaining copper in the narrow optimal range support plant enzyme activity, disease resistance, and strong crop development.
Organic soils are high in copper, but that doesn’t mean it’s in a form that plants can use. There is a fine line between optimal copper and toxic copper levels in soil and plant tissue. This metal nutrient affects most of the major biochemical reactions in plants. Optimal copper levels means your plants develop at their best. Too much or too little, and plants suffer.
Copper is essential for normal plant growth and development. It activates enzymes in a number of plant growth processes, including chlorophyll formation and protein synthesis. Copper is important for plant immune system functions, creating disease resistance. It is necessary to form lignin, an essential component of cell walls. It’s also been tied to vitamin A production.
Hidden Hunger on Organic Farms
Many crops may suffer from a condition called “hidden hunger.” Many micronutrient deficiencies aren’t immediately evident. Your soil may have adequate levels of copper and other micronutrients, but not optimal levels. This is like having a snack when your body tells you it needs a meal.
Over time, sub-optimal copper levels impair the ability of a plant to activate immune system responses to fight off pathogens. Wheat and other small grains such as rice, barley, and oats are especially affected by copper deficiencies. Too little copper available for plant uptake in the soil compromises crop fertility and reduces grain yield. Unusual lodging conditions, among other problems, are symptoms of a copper deficiency.
Factors Affecting Plant Copper Uptake
Soil conditions affect the bioavailability of copper for plants. The two biggest factors affecting plant copper uptake are soil pH and soil organic matter. Nutrient interactions and biological activity within your soil also affect copper uptake. Let’s take a closer look.
Soil pH
Copper availability decreases as soil pH rises. Soils with a pH higher than 7.5 tend to have copper deficiencies. Even when soil tests show adequate copper levels, a high soil pH can lock copper in unavailable forms, leading to deficiency symptoms in your crops. As you might have guessed, copper deficiencies are more common in calcareous, high-lime soils and fields with long-term overliming due to their high pH levels.
Soil Organic Matter
Copper binds strongly to organic matter. This can keep copper in the soil rather than in a form that is available to plants. In soils with high organic matter, copper is often plentiful but tightly complexed. It requires microbial activity and root exudates to slowly release copper into plant-available forms.
Nutrient Interactions in the Soil
Copper may bind to organic matter, but it also bonds to nitrogen, oxygen, and sulfur. Excess nitrogen fertilization can reduce copper availability by encouraging nitrogen and copper to bind. Sulfur and oxygen-containing minerals can also tie up copper, especially under dry or highly oxidized soil conditions.
Biological Activity
Soil microbes play a crucial role in mobilizing copper in the soil. Microorganisms release organic acids, enzymes, and chelating compounds work with plant roots to solubilize copper and move it toward plant roots. Soils with active microbial communities and healthy root systems are better able to regulate copper availability naturally, a major advantage many organic farms have over conventional ones.
Optimizing Copper Levels on Your Organic Farm
Soil and plant tissue testing can determine if the soil has a copper deficiency. On organic farms, copper sulfate can be used as a foliar spray. For a mixed-use organic farm with livestock, there’s good news: manured fields are unlikely to ever have a copper deficiency.
At ST Biologicals, we recommend Attest-O as an organic foliar spray to optimize plant-available copper. Foliar application transports copper through the vascular tissue of the plant. It increases copper as a catalyst for photosynthesis and plant respiration. Attest-O gets copper in the right amount, at the right time, in the right place.
For advice on how to test and amend your organic soil for optimal copper levels, contact the ST Biologicals mentors today. We’re here to help you succeed. When soil speaks, we listen.
Copper and Organic Farming FAQs
Why can organic soils still have copper deficiencies?
Copper binds tightly to organic matter, especially in high–organic matter soils. This can keep copper present but unavailable to plants unless microbial activity and root exudates release it into plant-usable forms.
What is “hidden hunger” for copper on organic farms?
Hidden hunger occurs when copper levels are sub-optimal but not low enough to cause obvious visual symptoms. Crops may look healthy while experiencing reduced disease resistance, weaker structure, and lower yields over time.
Which crops are most sensitive to copper deficiency?
Small grains such as wheat, barley, oats, and rice are especially sensitive to low copper availability. Deficiencies can lead to lodging, poor fertility, reduced grain fill, and increased disease pressure.
How can organic farmers optimize copper availability safely?
Soil and tissue testing are the first steps to determine true copper needs. Targeted foliar applications, such as organically approved copper products, deliver copper efficiently without risking soil accumulation or toxicity.
