7 April 2000


MAIZE should be drilled as early as possible once soil temperatures are suitable and a good seed-bed has been prepared.

MGA agronomist Simon Draper says that new maize varieties seem to have better cold tolerance, so soil temperature is not as important as it once was.

But its pointless drilling seed until soil temperature is high enough for a rapid germination. He advises continuing to follow the 8C soil temperature rule.

Then, if ground conditions are right, drill. "Drilling early will produce benefits in terms of higher yields and early maturity. But there is a risk of frost damage upsetting final yield."

A frost will have the same effect as a later drilling. "A very harsh frost is needed to kill maize."

Maize will require some nitrogen to get off to a good start, says Mr Draper. But each field situation varies, meaning requirements for bagged fertiliser range from 0-150kg N/ha (0-120 units/acre).

Factors affecting requirements include farm yard manure and slurry applications, variety grown, sub-soiling practice, soil type, weather pattern and previous cropping and mucking history.

"Applying too much N will delay crop maturity. You end up with green leaf and maturity suffers, with poor cob formation reducing starch yield," says Mr Draper.

"Too little N and the crop will grow slowly in spring, producing small leaves and a small plant. You can lose 20-40% of potential yield."

But agronomist Martin Froment of ADAS Bridgets, Hants, says that maizes response to N applications has been poor in a number of trials. "On a low fertility site with a shallow or sandy soil my recommendation would be not to exceed 120kg N/ha."

Young plants require a small amount of nitrogen, but are more dependent on phosphate.

Responses to starter P fertiliser have been achieved in research at ADAS Bridgets even when soil P index is three, he says.

However, trials showed no benefit of applying more than 32kg of phosphate/ha (26 units/acre). Its possible that less could be used, he says. "This was the lowest rate tested, but only 1kg to 2kg/ha of extra phosphate was taken up by the maize during early growth."

Phosphate is normally applied as mono-ammonium phosphate. But on chalk soils, the lime it contains can react with fertiliser, releasing ammonia which can damage roots, so its best to use triple-super phosphate.

But there are concerns over using high rates of starter fertiliser, when manure is also being applied for continuous maize crops, he warns.

In this situation, the P surplus is building rapidly and its best to rotate maize with cereals or grass after three or four years to reduce P loading and cash in on soil fertility.

When manure is used it usually meets maizes potash requirements, even though they are high at 160 to 180kg/ha (130 to 144 units/acre) for a 12t/ha (5t/acre) crop, he adds.

For good early growth, maize also needs to have little competition from weeds, adds Mr Draper.

"Pre-emergence atrazine is still a popular choice for weed control in maize, because of its low price. But only use it on relatively clean fields, because it doesnt persist long enough," he says.

Where there are more weeds, he advises selecting products to use depending on the weeds present. &#42


&#8226 Drill by soil temperature.

&#8226 Consider starter P.

&#8226 Control weeds.

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