Boron (B) deficiency

What it does

Boron (B) deficiency affects cell wall biosynthesis and the structure and plasma membrane integrity.

It leads to reduction in plant height, death of growing points, and white discoloration and rolling of leaf tips.

Why and where it occurs

Boron deficiency is relatively rare especially in irrigated rice systems. It is not very common in rice, but can occur in the following soils:

• highly weathered, acid red soils, and sandy rice soils in China
• acid soils derived from igneous rocks
• soils formed from marine sediments
• high organic matter status soils

How to identify

• Check the leaves for symptoms. Symptoms usually appear first on young leaves. Tips of emerging leaves are white and rolled (similar to Calcium deficiency).
• In severe conditions, growing points can die, but new tillers continue to emerge.
• Plants also have reduced height.
• When infected at panicle initiation stage, B deficiency can cause plants to not produce panicles.
• To confirm B deficiency, bring soil and plant sample to a laboratory for testing.

Why is it important

Although rare in irrigated rice systems, B deficiency affects the rice crop throughout its growth cycle.

How to manage

The following general measures are recommended to prevent B deficiency:

• Manage water efficiently. Avoid excessive leaching or draining of water. B is very mobile in flooded rice soils.
• Where possible, apply slow-acting B sources (e.g., colemanite) at intervals of 2−3 years. B fertilizers have a longer residual effect in silty and clayey soils (apply 2−3 kg B ha^-1) than in sandy soils (apply 3−5 kg B ha^-1).
  
  In rice-wheat systems, B applied to wheat can alleviate B deficiency in the subsequent rice crop. Do not apply excessive amounts of B to avoid B toxicity.

There is currently no practical treatment option for B deficiency. Where possible:

• Apply B in soluble forms (borax) for rapid treatment (0.5−3 kg B ha^-1). Broadcast and incorporate it before planting. It can also be topdressed, or used as foliar spray during vegetative rice growth. Do not mix borax and fertilizer borates with ammonium fertilizers.

Reference:
Dobermann A, Fairhurst T. 2000. Rice: Nutrient disorders & nutrient management. Handbook series. Potash & Phosphate Institute (PPI), Potash & Phosphate Institute of Canada (PPIC) and International Rice Research Institute. 191 p.