Boron fertilizers

Boron fertilizers

Boron is included in boron fertilizers in the form of water-soluble boric acid. Among boron-enriched basic fertilizers, boron superphosphate and boron-magnesium fertilizers are used in agriculture:

Granulated boron superphosphate is a light-gray granule containing 18.5–19.3% P₂O₅ and 0.2–1% boric acid (H₃BO₃).

Double boron superphosphate contains 40–42% P₂O₅ and 1.5% boric acid.

Boron superphosphate is mainly used in sugar beet and flax growing areas. It is applied to sugar beet, flax, fodder root crops, grain legumes, buckwheat, sunflower, cucumber, vegetables, and fruit and berry crops. For basal application, the rate is 200–300 kg/ha; in rows at sowing — 100–150 kg/ha. For flax, cucumber, vegetables, and fruit and berry crops — 150 kg/ha; for flax in rows — 50 kg/ha. For buckwheat, sugar beet, vegetable crops, peas, maize, cotton, seed plants of clover and alfalfa, boron superphosphate is applied at 300–350 kg/ha. For flax, strawberries, and cucumber, the rates of boron superphosphate are reduced by half. Boron-magnesium fertilizers are best applied in rows — 30–55 kg/ha — or broadcast — 100 kg/ha — simultaneously with other mineral fertilizers.

Boron-magnesium fertilizer is a gray powder that is a by-product of boric acid production. It contains up to 13% boric acid, or 2.2% B, and 15–20% magnesium oxide. It is applied to sugar beet, fodder root crops, grain legumes, buckwheat, and flax; in mixtures with other fertilizers it is applied at a rate of 20 kg/ha.

Boric acid is a finely crystalline white powder. It contains 17% boron and is highly soluble in water. It is used for foliar feeding at a rate of 500–600 g/ha for seed plants of perennial grasses and vegetable crops; for fruit and berry crops — 700–800 g/ha; for pre-sowing seed treatment — at a rate of 100 g boric acid per 100 kg seeds.

Borax, or sodium tetraborate, the crystalline salt of boric acid (Na₂B₄O₇⋅10H₂O), contains 11% boron.

Boron-containing nitroammophoska is a combined fertilizer containing 0.15% boron. It is applied during primary soil cultivation for all crops.

Boron datolite fertilizer is obtained from datolite rock (2CaO⋅B₂O₃⋅2SiO_y⋅2H₂O) by decomposition with sulfuric acid, with boron converting to boric acid (H₃BO₃). The boron content is about 2%, or 12–13% boric acid. Boron datolite fertilizer is a light-gray powder with good physical properties. It is mainly used for soil application and can be used for seed treatment.

Boracite meal (CaO⋅MgO⋅3B₂O₃⋅6H₂O) contains about 10% B. It is ground boron ore without preliminary processing. When finely ground, boron becomes available to plants.

Effectiveness of boron fertilizers

Different agricultural crops respond differently to elevated boron content in soil. For example, cereal crops suffer from excess when the content of mobile boron is 0.7–8.8 mg/kg soil, while alfalfa and beet tolerate boron concentrations in soil above 25 mg/kg soil. A content of boron in mobile form above 30 mg/kg soil can cause severe diseases of plants and animals.

The toxicity of boron is influenced by the amount and ratio of other nutrients. Good supply with calcium and phosphorus increases crop requirements for boron supply.

The importance of boron increases under liming of acidic podzolic soils, since liming reduces boron availability, fixes it in soil, and delays its uptake by plants. Application of boron fertilizers on limed soils eliminates heart rot of root crops and potato scab.

High effectiveness of boron fertilizers is observed on sod-gley and limed sod-podzolic soils. This is explained by the conversion of boron on limed soils into a poorly available form. It is partly fixed biologically, since liming stimulates biological processes.

On light soils, crop need for boron fertilizers appears at a content of 0.2 mg/kg soil; on loamy soils — 0.3 mg/kg soil. In dry years it increases; in wet years it decreases.

Soils poor in boron include sod-podzolic, sod-gley, waterlogged soils of light texture, red soils, humus-carbonate soils, leached chernozems, sierozems, and peaty soils. In tundra soils, total boron content is 1–2 mg/kg, mobile boron up to 0.1 mg/kg; in sod-podzolic soils, respectively 2–5 and 0.04–0.60 mg/kg.

For the Non-Chernozem zone, boron application is advisable when the content of mobile forms is less than 0.2–0.5 mg/kg soil; in the Chernozem zone — 0.30–0.65 mg/kg soil.

Application of boron on poor soils increases the yield of flax straw by 0.2–0.3 t/ha, sugar beet — on average by 4.5 t/ha, and increases sugar content by 0.3–2.1%. On sod-podzolic, sod-gley, peat-bog, and gray forest soils, the yield of flax seeds from the use of boron fertilizers increases on average by 0.8–1.0 centner/ha, fiber — by 0.7–0.8 centner/ha. Fiber quality improves.

The positive effect of boron fertilizers is manifested on seed plants of perennial leguminous grasses, primarily on limed sod-podzolic soils. This is explained by the fact that liming in combination with organic and mineral fertilizers promotes vegetative mass development; however, even on well-limed soils, boron deficiency arises for the development of buds and flowers. For this reason, with boron deficiency, mass development is delayed. Boron fertilizers increase clover seed yield by 0.5–1.0 centner/ha.

Application of boron fertilizers

Boron fertilizers are used for soil application, pre-sowing seed treatment, and foliar feeding. For soil application, boron superphosphate and boron-magnesium fertilizers are mainly used. The latter can be used for dusting seeds. For pre-sowing application to soil under sugar beet, buckwheat, vegetable crops, peas, maize, cotton, seed crops of clover, alfalfa, and other crops, a rate of 1 kg/ha boron is recommended; under flax, strawberries, and cucumbers — 0.5 kg/ha.

Boron-magnesium fertilizers are more effective on light sandy soils, where plants are responsive to magnesium. The broadcast application rate with incorporation into soil before sowing is up to 100–150 kg/ha. It is better to mix the fertilizer and apply it together with mineral mixtures. The rate for row application at sowing is 30–35 kg/ha.

Pre-sowing seed treatment is carried out by spraying or dusting. Spraying is done with a boric acid solution at a concentration of no more than 0.05% (1 g boric acid per 2 L water). Consumption is 2 liters of solution per 1 centner of seeds. When dusting seeds with boron-magnesium fertilizers, consumption is 300–500 g per 1 centner of seeds. It is advisable to combine dusting with dressing.

Foliar feeding is carried out with a boric acid solution at a rate of 100–150 g per 300–400 L water using ground tractor sprayers. For aerial feeding — 100–150 g per 100 L water. Foliar feeding of crops with boric acid solution is carried out when the vegetative mass is well developed: for sugar beet — before the leaves close in the rows; for maize — at the tasseling stage; for clover, alfalfa, peas, and other crops — during budding to early flowering. Spraying is carried out in calm dry weather, in the morning or evening hours.

For plants, the content of mobile, water-soluble boron is important; its presence depends on the parent rock and soil texture. The heavier the soil texture, the higher the boron content. The assimilable form of boron (boric acid) is weakly fixed by soil and can be leached by precipitation. Therefore, soils with sufficient and excessive moisture are poor in mobile forms of boron. The content of available forms is influenced by the content of aluminum and iron hydroxides.

References

1. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. B. A. Yagodin. Moscow: Kolos.
2. Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. V. G. Mineev. Moscow: D. N. Pryanishnikov All-Russian Research Institute of Agrochemistry Press.
3. Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: A Textbook. Moscow: FORUM.