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Boron foliar nutrition in chilli

Foliar application of boron during the pre-flowering and early flowering stages is a standard practice in chilli cultivation to reduce flower and bud drop and to improve fruit set. Boron is essential for pollen viability, pollen tube growth, cell-wall pectin cross-linking and sugar translocation, all of which are critical during the reproductive transition.

Composition

The two sources used most commonly on chilli are:

  • Solubor (disodium octaborate tetrahydrate, DOT): 20-20.5% B, fully water soluble, dust-free, designed for foliar and fertigation use; marketed by Tata Rallis and U.S. Borax.
  • Boric acid (H3BO3): 16.5% B, low cost, water soluble; widely available.

Both are notified under the FCO micronutrient schedule.

Mode of action

Foliar-applied boron penetrates the leaf cuticle and stomata and is translocated to active sinks, including expanding flower buds and growing pollen. In boron-deficient plants, pollen is sterile or has reduced tube growth, leading to flower abscission and poor fruit set; replenishing tissue boron during flowering corrects this failure. Roughly 45% of Indian arable soils are reported boron deficient, which means foliar correction during reproduction is often necessary even where some boron has been applied basally.

Target use and dose

In chilli:

  • Concentration: 1-2 g of Solubor (or boric acid) per litre of water.
  • Timing: at the appearance of the first flower buds, repeated 10-15 days later at peak flowering.
  • Tank-mixing: commonly combined with calcium nitrate to address simultaneous Ca-B deficiency in fruit set; for compatibility cautions see Calcium Magnesium Foliar.

Similar regimes apply to capsicum, tomato, brinjal and pomegranate. Excessive doses cause leaf-margin scorch, so the rate must be respected.

Safety and regulatory status

FCO-notified micronutrient fertiliser. The margin between deficiency and toxicity is narrow: soil B above 5 ppm or repeated heavy foliar sprays cause toxicity symptoms in sensitive crops. No pre-harvest interval at recommended rates.

See also: Boron Fertilizer, Calcium Magnesium Foliar, Multi Nutrient Fertilizer Blends, Edta Chelated Zinc.

References

  1. Solutions for India's Fortified Fertilizer Market. U.S. Borax.
  2. Boron 20. Indian Farmers Fertiliser Cooperative.