Copper fertilizers
Copper fertilizers — micronutrient fertilizers that meet the need of agricultural crops for the micronutrient copper.
Copper content in soils
Total copper content in soils ranges from 0.1 to 150 mg/kg of soil. In the arable layer, copper is mainly present in mobile form as the divalent copper cation in an exchange-adsorbed state. Copper is a constituent of soil minerals and organic matter. The greatest amount of copper is bound by montmorillonite and vermiculite, iron and manganese oxides, and iron and aluminum hydroxides. Stable complexes of humic and fulvic acids can form with copper; therefore, raised bogs, sod-carbonate, bog, waterlogged, sandy, and sandy loam soils are poor in copper. Liming of acidic soils reduces copper availability to plants, as it promotes fixation in the soil. Lime acts as an adsorbent of copper and, through alkalinization, creates conditions for the formation of stable complexes with organic compounds.
In soil, copper accumulates in organomineral complexes and partly in an exchange-adsorbed state. Copper availability decreases when pH rises from 5.5 to 6.0. Copper deficiency is clearly pronounced on uncultivated heathlands, on light soils and raised bog soils, sometimes on lowland bog soils. Copper deficiency in feed leads to animal diseases.
Plants experience copper deficiency, and soils are considered poor, when content in soils of the Non-Chernozem zone is less than 1.5–2.0 mg, in the Chernozem zone less than 2.0–5.0 mg per 1 kg of soil.
The need for copper fertilizers is mainly observed in the Northwestern, Central, and Volga-Vyatka regions of Russia.
Copper fertilizers are effective on peat, light sandy, and sod-gley soils. On drained peatlands, even with application of complete mineral fertilizer, a full yield of cereals and other crops can be obtained only with copper application. According to experiments, application of copper fertilizers on peat-bog and light sandy loam soils increases the yield of cereal crops by 0.2–0.5 t/ha.
Copper mobility in soil increases with acidification of the soil solution, decreasing organic matter and clay fraction content. Copper fixation is promoted by high content of organic matter and carbonates, alkaline reaction, and fine soil texture, with a large proportion of silt.
Wheat, oats, barley, grasses, flax, hemp, root crops, meadow clover, millet, sunflower, mustard, sugar and fodder beet, faba beans, peas, vegetable and fruit-and-berry crops respond well to copper fertilizers. The need for copper increases when high doses of nitrogen fertilizers are applied. Peas, vetch, lupine, hemp, flax, beet, vegetables, and fruit plantations suffer from copper deficiency in the soil.
Application of copper fertilizers
Agriculture’s need for copper fertilizers is met mainly through copper sulfate (cupric sulfate), copper-potassium fertilizers, and copper-containing industrial wastes.
Table. Assortment of copper fertilizers.
| Fertilizer | Active ingredient | Content of a.i. in water-soluble form, % |
|---|---|---|
| Copper sulfate (cupric sulfate) | CuSO4⋅5H2O, Cu | 92.0–98.0 |
| Cu | 23.4–24.9 | |
| Copper-containing powder | CuSO4 | 14–16 |
| Cu | 5–6 | |
| Pyrite (pyritic) cinders | Cu | 0.25 |
| K2O | 58.6±0.6 |
Copper sulfate, or copper sulfate pentahydrate, blue vitriol (CuSO4⋅5H2O) — a crystalline salt of a bluish-blue color, contains 25.4% copper, and is readily soluble in water.
Pyrite cinders are copper fertilizers of local importance, containing 0.2–0.7% copper, an industrial waste from sulfuric acid production. They contain impurities of iron, manganese, cobalt, zinc, and molybdenum. A disadvantage of pyrite cinders is the presence of arsenic, lead, and other heavy metals; therefore, their use requires systematic monitoring of potential contamination of soil, plants, and agricultural products. They are applied once every 4–5 years at a rate of 500–600 kg/ha in autumn under fall plowing or in spring under pre-sowing cultivation.
Copper fertilizers also include slags from zinc-electrolytic and copper-smelting plants containing 0.2–0.5% copper. Also, low-grade oxidized copper ores with a content of about 0.9%.
Pre-sowing seed treatment is carried out by spraying with 0.1–0.2% copper sulfate solution or by dusting. The solution consumption for spraying is 6–8 L per 100 kg of seeds. For dusting 100 kg of seeds, 50–200 g of well-dried and ground copper sulfate is used. Dusting is combined with dressing. Dusting with copper sulfate is convenient for flax, whose seeds become mucilaginous when soaked. For foliar top dressing, the application rate is 200–300 g per 1 ha of crops, or a 0.02–0.05% solution. For ground spraying of row crops — 300–400 L/ha, for aerial top dressing — 100 L/ha.
For soil application, pyrite cinders, copper-containing slags, and low-grade oxidized copper ores are used. Pyrite cinders and slags are applied at 5–6 cwt/ha once every 4–5 years, low-grade oxidized copper ores — 2–3 cwt/ha. Fertilizers are incorporated with a plow during fall plowing, or with a cultivator.
Under conditions of copper deficiency in the soil, copper fertilizers give yield increases: spring wheat — by 0.2–0.5 t/ha, barley — by 0.2–0.3 t/ha, oats — by 0.4–0.6 t/ha, green mass of maize — by 2.1 t/ha, cobs — by 9–13%. Copper fertilizers improve product quality: protein content in cereal grain increases, vitamins in vegetables, fruits, and berries increase, and the quality of flax and hemp fiber improves.
References
- Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. B. A. Yagodin. Moscow: Kolos.
- Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.
