Boron in plant life
Boron was discovered in plant ash in the 1950s. Boron is abundant in nature in the form of the oxygen-containing minerals boric acid (H3BO3) and sodium tetraborate, or borax (Na2B4O7⋅10H2O).
The average content of boron in plants is 0.0001%, or 1 mg per 1 kg of weight. Dicotyledonous plants need this element the most. Significant content is noted in flowers, especially in stigmas and stolons. In plant cells, most of the boron is concentrated in cell walls. Boron enhances pollen tube growth, pollen germination, and leads to increased number of flowers and fruits. Boron deficiency impairs the process of seed ripening. It reduces the activity of oxidative enzymes, affects the synthesis and movement of growth stimulants.
Plants have a lifelong need for boron. It is not reutilized, so when it is deficient, young growing organs suffer. Disease and die-off of growth points occur.
In plants, boron is involved in carbohydrate, protein and nucleic acid metabolism. Its deficiency leads to disruption of synthesis, transformation and movement of carbohydrates, formation of reproductive organs, fertilization and fruiting.
According to M.Y. Shkolnik’s concept, boron deficiency in dicotyledonous plants leads to disturbances in physiological processes:
- accumulation of phenols occurs;
- phenolic auxin oxidase inhibitors increase accumulation of auxins;
- nucleic metabolism and protein synthesis are disrupted;
- cell wall structures and cell division processes are disrupted;
- tissue turn browning occurs due to increased permeability of tonoplast vacuoles and penetration of polyphenols into cytoplasm under the influence of phenols.
The main physiological role of boron is to participate in the exchange of auxins and phenolic compounds. Boron is not a part of enzymes, but it activates auxin oxidase and p-glucosidase.
Boron deficiency leads to plant damage by dry rot (root crops), brown rot (cauliflower), hollowness (turnips and rutabaga), bacteriosis, yellowing (alfalfa), drying tops (tobacco), broken fertilization in flax, sunflower growing point dies off.
Sunflowers, alfalfa, fodder crops, flax, rice, sauerkraut, vegetable crops, and sugar beets are sensitive to boron deficiency.
Application of boric fertilizers provides an average increase in sugar beet root crops yield of 2,5-5,0 t/ha and sugar yield of 0,4-0,8 t/ha. Increase of flax seed yield – on average 0.08-0.15 t/ha. On sierozem soils of Central Asia boron fertilizers increase the yield of raw cotton by 0.15-0.45 t/ha.
Boron improves product quality: the content of protein, sugars, starch, vitamins increases, the oil content of seeds increases, their germination and germination energy improves. Thanks to the fact that boron improves photosynthesis and carbohydrate exchange, it favors outflow of sugars from leaves and their inflow to reproductive organs.
Sugar beet, fodder root crops, flax, clover, alfalfa, potato, corn, sunflower, buckwheat, legumes, cotton, vegetable and fruit crops are the most responsive to boron fertilizers. Grain spiked crops respond poorly. Boron fertilizers used for sugar beet seeds increase the yield of seeds, improve their quality, increase their germination and germination energy. In all experiments boron fertilizers resulted in an increase in sugar content by 0,3-2,15%.
Excess of boron causes plant toxicosis, and boron is primarily accumulated in the leaves. It appears as a peculiar burn of lower leaves, marginal necrosis appears, leaves turn yellow, die off and fall off.
Effectiveness of boric fertilizers
Different crops respond differently to elevated boron content in the soil. For example, grain crops suffer from excess at mobile boron content of 0.7-8.8 mg/kg soil, alfalfa and beets tolerate boron concentration in the soil above 25 mg/kg soil. The content of boron in mobile form of more than 30 mg/kg of soil can cause severe diseases of plants and animals.
The toxicity of boron is influenced by the amount and ratio of other nutritional elements. A good supply of calcium and phosphorus increases the demand for boron in crops.
The importance of boron increases under conditions of liming acidic podzolic soils, as liming reduces the availability of boron, fixes it in the soil and delays its arrival in plants. Application of boric fertilizers on limed soils eliminates diseases of root rot of heart and potato scab.
High efficiency of boron fertilizers is noted on sod-gley and calcareous sod-podzol soils. It can be explained by transition of boron on calcareous soils in the hard-to-reach form. Partly it is fixed by biological way, as liming stimulates biological processes.
On light soils the crops need boron fertilizer at 0.2 mg/kg of soil, on loamy soils – 0.3 mg/kg of soil. It increases in dry years and decreases in wet ones.
Boron is poor in sod-podzolic, sod-gleyey, waterlogged soils of light granulometric composition, red earth, humus-carbonate, leached chernozems, gray soils, peaty soils. In tundra soils the gross boron content is 1-2 mg/kg, mobile – up to 0,1 mg/kg, in sod-podzolic soils – 2-5 and 0,04-0,60 mg/kg, respectively.
For the Non-Black Earth zone boron application is advisable when the content of mobile forms less than 0,2-0,5 mg/kg of soil, in the Black Earth zone – 0,30-0,65 mg/kg of soil.
Boron application on poor soils increases the yield of flax straw by 0,2-0,3 t/ha, sugar beet – an average of 4.5 t/ha and an increase in sugar content by 0,3-2,1%. On sod-podzolic, sod-gley, peat-bog and grey forest soils the yield of flax seeds from application of boric fertilizers increases on the average by 80-100 kg/ha, fiber – by 70-80 kg/ha. Quality of fiber improves.
Positive effect of boric fertilizers is shown on seed plants of perennial leguminous grasses, first of all, on sod-podzol soils with limestone. This is explained by the fact that liming in combination with organic and mineral fertilizers develops vegetative mass, but at the same time, even on well limed soils, there is a deficiency of boron for development of buds and flowers. For this reason, when boron is lacking, the development of the mass is delayed. Boric fertilizers increase the clover seed yield by 50-100 kg/ha.
Table. Efficiency of boric fertilizers on sod-podzolic soilsYagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Sugar beet (peat-bog soils)|
Boron is included in boric fertilizers in the form of water-soluble boric acid. Of boron-enriched basic fertilizers, boron-superphosphate and boron-magnesium fertilizers are used in agriculture:
|Boric acid technical|
Granulated borosuperphosphate is a light gray granule containing 18.5-19.3% P2O5 and 0.2-1% boric acid (H3BO3).
Double borosuperphosphate contains 40-42% P2O5 and 1.5% boric acid.
Borosuperphosphate is mainly used in beet-growing and flax-growing areas. It is used for sugar beet, flax, fodder root crops, grain legumes, buckwheat, sunflowers, cucumber, vegetables, fruit and berries. It is necessary to apply a 200-300 kg/ha dose for main application and 100-150 kg/ha dose for sowing in the rows. Under flax, cucumber, vegetables, fruits and berries – 150 kg/ha, under the flax in the rows – 50 kg/ha.
Boron-magnesium fertilizer is a gray powder, which is a waste product of boric acid production. It contains up to 13% boric acid, or 2.2% B, and 1520% magnesium oxide. It is used for sugar beet, fodder root crops, grain legumes, buckwheat and flax; in mixture with other fertilizers it is applied at the rate of 20 kg/ha.
Boric acid is a fine crystalline powder of white color. It contains 17% of boron and is well soluble in water. It is used for foliar dressing at a dose of 500-600 g/ha for perennial grasses and vegetable crops, for fruit and berry crops – 700-800 g/ha; for pre-sowing seed treatment – 100 g boric acid per 100 kg of seeds.
Table. Application of boric fertilizers for various crops Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
|Borosuperphosphate (0,2% B)||Sugar beets, forage root crops, cereals, pulses, buckwheat||In the soil, with the main application of|
|In the rows, when sowing|
|Flax||In the soil, with the main application of|
|In the rows, when sowing|
|Cucumber, vegetables, fruit and berries||In the soil, with the main application of|
|Boric acid (17% B)||Sowing perennial grasses and vegetable crops to produce seeds||For pre-sowing tillage|
|Fruit and berries||Non-root fertilizing|
|Boron-magnesium fertilizer (2,2% B)||Sugar beets, forage root crops, leguminous crops, buckwheat, flax||In the soil in a mixture with mineral fertilizers|
Borax, or sodium tetraboric acid, a crystalline salt of boric acid (Na2B4O7⋅10H2O), contains 11% boron.
Boron-containing nitroammonium phosphate is a compound fertilizer containing 0.15 percent boron. It is applied to all crops during primary tillage.
Boron-datolite fertilizer is made from datolite rock (2CaO⋅B2O3⋅2SiOy⋅2H2O) by decomposition with sulfuric acid, with which boron transforms into 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 primarily 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 ores without any preliminary treatment. In finely ground form, boron is converted to a plant-available state.
Application of boron fertilizer
Boron fertilizers are used for soil application, seed pre-sowing treatment and foliar dressing. Boron superphosphate and bormagnesium fertilizer are mainly used for soil application. The latter can be used for seed sprinkling. For pre-sowing application to the soil for sugar beets, buckwheat, vegetable crops, peas, corn, cotton, seed crops of clover, alfalfa and other crops a dose of 1 kg/ha of boron is recommended, for flax, strawberries and cucumbers – 0.5 kg/ha.
Boron-magnesium fertilizer is more effective on light sandy soils where plants are responsive to magnesium. Dose of spreading with embedding in the 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 dose when applied to the rows at sowing is 30-35 kg/ha.
Seed treatment before sowing is carried out by spraying or powdering. Spraying is carried out by solution of boric acid with concentration not more than 0.05% (1 g of boric acid per 2 liters of water). Consumption is 2 liters of solution per 100 kg of seeds. When seeds are powdered with boric-magnesium fertilizer consumption is 300-500 g per 100 kg of seeds. It is advisable to combine the powdering with treatment.
Root feeding is carried out by a solution of boric acid at the rate of 100-150 g per 300-400 liters of water by ground tractor sprayers. During aerial feeding – 100-150 g per 100 liters of water. Cultures are fertilized by a solution of boric acid when vegetative mass is well developed: sugar beet – before the tops close in rows, corn – in the phase of panicles; clover, alfalfa, pea and other cultures – during budding and early flowering. Spraying is carried out in windless dry weather, in the morning or evening hours.
For plants, the content of mobile, water-soluble boron depends on the soil-forming rock and granulometric composition of the soil. The heavier the granulometric composition, the higher the boron content. The assimilable form of boron (boric acid) is poorly fixed by the soil and can be washed out 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.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of Agronomy: Tutorial/Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.