2 February 1996

when going gets tough its time to reduce seed rates

UNLIKE all other crops, seed rates for maize should be reduced in poorer growing conditions and increased on warm fertile sites.

"While higher rates will probably increase overall forage quantity, higher populations increase competition between plants," says MGA agronomist Simon Draper. Extra competition will suppress cob quality – which determines forage dry matter content and its digestibility. "Maturity will also be delayed and the risk of lodging increased," he says.

"Seed is normally supplied in acre packs which suit most situations. But seed rates should be adjusted downwards where the crop is being grown at altitudes above 400ft, on northerly sites. On poor seed-beds or in higher yielding areas seed rate should be increased," he says.

If quality is the prime consideration and where previous crops have failed to reach 30% DM at harvest, seed rates should be reduced. But rates must still be sufficient to give the required population anticipating some seed loss.

"A seed loss of 10% can normally be expected. Under poorer growing and seed-bed conditions this could be up to 12 to 15%. Where there are high levels of slugs and wireworms losses will increase still further," he says.

He advises target plant populations of about 80,000 to 100,000/ha (32,000/acre to 40,500/acre) which can be increased or decreased depending on the site.

"Where 90,000 plants/ha (36,250/acre) are required the rate should be about 102,000/ha (41,000/acre). &#42


TABLE 1: Seeding rates and plant population table

Favourable conditionsUnfavourable conditions*

TargetSuggestedTargetSuggested

populationseed ratepopulationseed rate

35,000/acre40,000/acre33,000/acre38,000/acre

86,500/ha98,800/ha81,500/ha93,900/ha

*Higher altitudes, cold soils, areas exposed to wind, areas of low rainfall, and late sowing.

Source: HUNTSEEDS

TABLE2: Seeding rates and plant population

How many seeds should be sown and at what distance?

Seeds to be (/ha)80,00090,000100,000110,000

sown per given area(/acre)32,40036,40040,40044,500

Seed spacing in

row in cms with

7.5cm row spacing16.714.813.312.1

Seed/m of row length

with 7.5cm row spacing6.06.87.68.3

Source: HUNTSEEDS

Seed rates for maize should be reduced in poor growing conditions.