Gypsum application at pegging in groundnut

Gypsum (CaSO4.2H2O) is a critical soil amendment in groundnut cultivation because of the crop's unusual physiology: groundnut pods develop underground, and the developing kernel takes up calcium directly from the soil in the pegging zone rather than through the xylem stream from the roots. Adequate calcium availability at the time of peg penetration and pod fill is therefore essential for pod yield and kernel quality.

Composition

Agricultural gypsum supplies approximately 21% calcium and 17% sulphur, both in plant-available sulphate forms. The product is sold as a coarse-ground powder and is FCO-notified as a soil amendment. Phospho-gypsum, a by-product of the phosphoric acid industry, is the most widely available source in India.

Mode of action

When applied at the pegging stage, gypsum dissolves slowly in the soil moisture of the pegging zone and supplies free Ca2+ ions to the developing kernel. Calcium is incorporated into pod wall and kernel structure, while the sulphate fraction contributes to the synthesis of sulphur-containing amino acids and to oil quality. Inadequate calcium at pegging results in "pops" (empty pods), poorly filled kernels and increased aflatoxin susceptibility.

Target use and dose

ICAR-DGR Junagadh, ANGRAU and TNAU package-of-practices recommend approximately 400-500 kg per hectare of gypsum at the peg-down/flowering stage (approximately 30-35 days after sowing). An alternative schedule splits the dose as 50% basal at sowing plus 50% at peg initiation. Application is by side-dressing along the rows, with light incorporation, to place the gypsum in the pegging zone rather than below the rooting zone.

Adoption and yield impact

Gypsum application at pegging is now a near-universal practice in commercial groundnut cultivation across Gujarat, Andhra Pradesh, Karnataka and Tamil Nadu. Published trials report significant improvements in pod, kernel, protein and oil yield compared with no-gypsum controls, with the largest gains on sandy, low-calcium soils. Gypsum also improves soil structure on saline-sodic soils, providing a secondary reclamation benefit.

References

Package of Practices of Groundnut. ICAR-Indian Institute of Groundnut Research.
Groundnut. TNAU Agritech Portal.