by Christian Schmalz, Marketing Director, UlexAndes-USA
The impact of micronutrients on plant development is well researched. Despite the rather small quantities, micronutrients play a complex role in crop development and health. Micronutrient sourcing is becoming increasingly critical as low quality products continue to enter the market. The Andes Mountains region is renowned for its rich deposits of minerals. They have a long tradition of metallurgy and mining allowing Chile and Peru to become one of the most important micronutrient sources in the world. Regardless of the source, product awareness of critical factors including bulk density, SGN, hardness, dust levels and manufacturing processes will help protect your investment.
Copper: The element
For more than 10,000 years, copper has been one of the most useful metals available to man and was one of the first metals worked. Copper has withstood the test of time, enjoying a wide range of uses over the centuries from ointments to dyes to preserving timber to molluscicides and power transmission. Copper is a major industrial metal, ranking only behind iron and aluminum in terms of consumption. The vast majority of copper is used in electrical equipment (conducts heat and electricity well) construction (roofing and plumbing) and industrial machinery (heat exchangers).
The major copper-producing countries are Chile, Peru and China. Roughly 20 mining companies produce close to 60% of the copper worldwide. Copper metal does occur naturally, but by far the greatest source is in minerals such as chalcopyrite, chalcocite and bornite. Copper naturally associates with sulphur in ore deposits, but the average grade of copper is below 0.6%. Liberating the copper requires several chemical, physical and electrochemical processes. Smelting, leaching and electrolysis processes are dictated by the parent ore mineral composition.
Copper use in agriculture was first documented in 1761 to inhibit seed-born fungi. By 1807, copper sulphate was standard treatment to control bunt of wheat. It was so effective
at controlling bunted wheat, this disease now has limited economic impact. Arguably, the most important agriculture breakthrough for copper sulphate occurred in Bordeaux, France, in 1880 as a treatment for fungus diseases. The Bordeaux Mixture (copper sulphate and lime) is still the gold-standard fungicide in vineyards, orchards and gardens. Deficiencies occur in high organic matter and sandy soils
Copper (Cu+2) is a micronutrient or trace element, which by definition, is an essential element found in less than 0.01% of the plant dry matter. Copper sulphate is an inorganic compound that combines sulphur with copper. Copper sulphate pentahydrate (CuSO4:5H20) is the most commonly encountered salt and is the preferred source for fertilizer.
Because micronutrients are located within the soil, this single component plays a crucial role in bioavailability. The impact of cation exchange, organic matter or solid minerals determines the plant uptake ability. Copper is taken up as Cu2+ (cupric ion) by plants primarily through diffusion. Therefore, cation exchange is a significant factor in copper supplementation.
Role: Copper is an essential redox, active transition metal, cofactor responsible for activating enzymes and catalyzing reactions necessary for plant growth. It is also closely linked to vitamin A production and protein synthesis. Plants also rely on copper for carbohydrate and chlorophyll production as well as lignin synthesis and nitrogen processes. Many crops respond positively to proper copper supplementation, but grains-wheat, barley and legumes are known high users of copper.
Organic Matter: Copper is more tightly bound to organic matter than other micronutrients which can reduce its bioavailability. Copper may also form chelates (Greek for ‘claw’) with soluble organic matter. Metallic chelates are complexes of metal ions bound to organic molecules (ligands). Positively charged metal ions, such as Cu+2, readily react with negatively charged hydroxide ions (OH-), making them unavailable to plants. Hydroxide ions are abundant in alkaline or neutral soils and soil-less media.
Synthetic chelates, most commonly manufactured with EDTA, and are an option in micronutrient management. These chelation compounds are more stable in compromised soil, thereby increasing the plant availability of the metal micronutrients due to the ligand (a molecule that binds to a central metal atom) coating of the metal ion protecting it from the surrounding hydroxide (OH-) ions. Like all micronutrients, copper is an essential cofactor and a toxic element in excess or deficiency.
Soil pH: Copper availability paradoxically decreases as pH increases primarily due to the decreased solubility. Soils that contain higher amounts of oxides and carbonates also tend to have low copper availability.
Consistent with most micronutrients, copper has a narrow therapeutic range. Copper toxicity can also persist for an extended period due to its low mobility. Toxicity affects seed germination, root system development and plant vigor.
Copper deficiency symptoms vary by crop. Because copper is immobile, and it tends to bond to organic molecules like humic and fulvic acids, deficiency symptoms first appear in new growth tissue. Copper also interacts with Zn and Fe impacting uptake.
Soil applications of copper sulphate before seeding is most common either by broadcast or banded with other fertilizers at a rate of 4 lbs of copper 25/acre. Efficiency is improved when combined with water soluble fertilizers Ideal physical properties for granular copper is a round, prilled granule with a screen analysis of 2-3mm and a bulk density of 50-65 lbs/cu ft. Hardness should able be above 6 lbs pressure and ideally have a low dust level. Foliar applications can also be an effective way to correct known copper deficiencies.