3 March 2000

Beware P surpluses when using starter

By James Garner

MAIZE growers are warned to be aware of phosphate surpluses when using starter phosphate applications.

ADAS Bridgets researcher Martin Froment told growers at MGAs annual conference at Stoneleigh, Warks, to be aware of environmental impacts when using starter P. He warned that excess phosphate could leach into water courses and cause eutrophication.

But he did not suggest that growers should forgo using starter P in the right conditions.

"Trials at ADAS Bridgets show that starter P improves early and mid-season plant growth, but by harvest this has evened out and there is no yield benefit."

But while there may appear to be little yield benefit from using it in good maize growing areas, growers in marginal areas, which have earlier harvest dates and slower growth in spring, may find using starter P benefits their crops. Typically, growing maize leaves a surplus of P. When applying 50,000 litres/ha of slurry or 50t/ha (20t/acre) of FYM, the crop receives 50kg/ha-150kg/ha (40 units/acre to 120 units/acre) of P. Typical offtakes of P in maize are only 50kg/ha (40 units/acre), so when P fertiliser is used as well, surpluses build up rapidly, said Mr Froment.

At ADAS Bridgets, maize is rotated around the farm to ensure that too large a phosphate surplus does not built up. "After a couple of years of fertility building we would then move maize and cash in on the soils surplus phosphate."

There is little yield benefit from using starter P in good maize growing areas, says ADAS researcher Martin Froment.