Ca tackles rust spot in spuds
CALCIUMS role in reducing internal rust spot in potatoes was well demonstrated in trials last season, according to Hydro Agri.
After widespread problems in 1997 buyers are likely to be particularly wary of the disorder this year, warns the firms Miles Harriman.
The Norfolk trials used Saxon, Estima and Squire and compared top dressings of ammonium nitrate and calcium nitrate at tuber-initiation. Both supplied 100kg/ha (80 units/acre) of N, with the latter also giving 122kg/ha (98 units/ acre) of calcium.
On Squire calcium almost halved rust spotting from 30% to 16.7% of tubers. In Estima the effect was less dramatic, the level dropping from 17.3% to 14.4%. Saxon treated with ammonium nitrate showed just 3.3% spotting, with calcium it was entirely rust-free.
Timing is critical
Timing is critical, notes Mr Harriman. He is also keen to see more work on a wider range of varieties to determine the true varietal effects.
Using calcium nitrate instead of ammonium nitrate at a more typical top dressing level, providing 60kg/ha (48 units/acre) of N, is still likely to offer useful benefits, Mr Harriman adds. He urges growers to try comparative field strips to identify the advantages for themselves. Extra cost would be about £38/ha (£15/acre).
• Omex advocates a spray-on approach to calcium (Arable, Apr 10). "If you put on calcium nitrate the calcium goes into soil solution and can become locked up with phosphate," warns Andy Eccles. "You can then also reduce the solubility of any applied phosphate, and soluble phosphate is important for potatoes. That is why we advocate the foliar route."