19 April 1996

Total cover could be a whole lot better

MAIZE grown under plastic without holes could reduce costs and improve crop quality if on-farm results are repeated in studies this year.

This is the expectation of Fergal Keane, Eire-based crop consultant for maize breeder Pioneer Hi-Bred. His reasoning is based on the increased early vigour noticed in plants that had failed to emerge through plastic after a fault with a drill.

"Some plants were drilled out-of-line with holes in the plastic. These were far advanced compared with plants that had emerged successfully," explains Mr Keane.

Now a number of research institutes in Eire have set up studies into total plastic cover for the coming year.

"If this increased early vigour proves to be a response to total cover it could produce an earlier harvest and a higher grain content," says Mr Keane.

An initial study, conducted on farm, compared soil surface temperatures around the plant in holed plastic, bare ground and total cover.

Temperatures around the plants under holed plastic were between 2C (3.6F) and 4C (7.2F) higher than on bare ground. With total cover, temperatures were 6C (10.8F) higher than those recorded on bare ground.

In addition, total cover provides a further insurance against plants being killed or burnt off by frost.

"Even at the seventh leaf stage we have plants killed by frost. And in holed plastic, it can burn-off the upper part of the plant.

"Even though the growing point is about an inch above the soil surface and plants recover, this frost damage causes a significant growth check," says Mr Keane.

Normally, plastic is laid and punctured by the drill as plants are drilled directly through it. For the covered crop a conventional maize drill and plastic layer were modified to drill the crop and lay plastic over the top.

"This machine is less complex than current plastic laying/drill combinations, making it potentially cheaper," says Mr Keane.

A more flexible plastic has to be used, laid with more slack in it, to allow the plant to grow without causing damage to the stem.

Mr Keane says: "Costs for maize growing in Ireland are about £240/acre from drilling to the clamp. Polythene prices vary according to grade and degradability but it is available in Eire for £75/ acre.

"There is also an extra £5 contractor cost for drilling with plastic."

Total cover costs a further £8 because plastic must be split using tractor-mounted discs when the crop reaches a certain growth stage. Correct timing of plastic ripping is essential – a few days out and the crop could be ruined," he says.

"Plastic must be ripped at seventh leaf stage. This is before plants get too large to prevent permanent damage to the stems as the plant is bent over and when the danger of frost is over.

"Tractor-mounted spiked discs were used to break the plastic and damage to plants was minimal, partly because the plastic had more slack in it than conventional holed plastic," he adds. &#42

Jonathan Riley

Frost attack can damage maize plants grown under conventional holed plastic. Total plastic cover improves crop quality and could cut costs, recent research suggests.