DEFICIENCIESTHREATEN YIELDS

1 June 2001

DEFICIENCIESTHREATEN YIELDS

SEVERE and worsening deficiencies of both phosphate and potash in soils could be putting cereal yields at risk.

Unless growers tailor application rates to take account of grain yield, P and K off-take and soil reserves yield could be jeopardised, says John Hollies of the Potash Development Association.

"Financial and weather effects have had a catastrophic effect on P and K use since last harvest," he says. "It could be down by as much as 25% on last year, which was itself the third year in a row of reduction."

The difference between off-take in grain and straw and the amount applied is widening by about 30kg/ha a year for wheat. That is unsustainable as soil reserves are being severely eroded, he maintains.

Between 5-6kg of potash is removed with each tonne of wheat grain and the amount lost is at least doubled to 11-13kg if the straw is also carted off. With oats the off-take can be as much as 20kg.

MAFF statistics for 1995 showed 80% of wheat straw was baled and removed, most of it going for bedding on the same farm, so the lost nutrient was returned as manure. But straw is increasingly becoming a cash crop sold to livestock farmers, power stations or the packaging industry.

"It is absolutely vital for cereal growers to tailor P and K rates to crop need, based on expected yield, likely off-take and reserves available in the soil."

The revamped version of the FREE PK slide-rule Kalculator, which was to have been promoted at Cereals 2001, takes account of MAFFs latest RB209 advice to provide more targeted recommendations for specific soil types. Contact PDA (01994-427443) or pda@farmline.com

P&KSHORTFALL

&#8226 25% cut in usage.

&#8226 30kg/ha/year less on wheat.

&#8226 Severe yield loss possible.

&#8226 Match input to likely yield, offtake and soil reserves.

&#8226 5-6kg potash removed with each 1t of wheat grain. Double if straw also removed.

Missing P and K inputs can save money. But on borderline sites replace what is removed in grain and straw to guard against later yield loss, says PDAs John Hollies.