8 September 1995

Drought conditions make it harder to decide when to go

By Jonathan Riley

DECIDING when to harvest forage maize will be harder this year as drought conditions in some regions have caused uneven ripening within crops, says Maize Growers Association agronomist Simon Draper.

Harvesting date will be affected by a sites location, altitude, its aspect and the level of drought stress.

"Maturity of drought-hit crops stood still until it rained," he says. "Now the crops have begun to grow again but are picking up where they left off in terms of maturity. Crop condition will vary in a single field, making it difficult to work out when to harvest."

Maize silage dry matter should be about 30% at harvest and there are a number of tests to establish the dry matter content.

Thumbnail test

"Use the "Thumbnail" test," he says. "Grains at the top of the cob should have a soft cheese consistency and at the bottom be like hard cheese. Grains in the middle of the cob should just be able to take the imprint of a thumbnail.

"At this stage the cob would be about 50% DM and the resulting crop about 30% DM."

As a back-up to the thumbnail test the "milkline" test can be carried out by breaking a cob in half and looking for a white/cream line in the kernel.

"When the line is one- to two-thirds down the kernel the plant should be between 30% to 35% DM," says Mr Draper.

"The most accurate test is the oven test and is most useful in more marginal areas, where the harvest time can be more critical.

"Roughly chop three whole plants taken at random from different areas of the crop. Then mix them, take a 1kg sample of fresh material and put it in a tin in the bottom of an Aga or conventional oven at 100C overnight.

"Re-weigh the dried sample and divide the weight by 10 to give the DM%. To ensure all of the moisture has been removed put the material back in the oven and later calculate the DM again," he says.

This year he predicts cutting heights will be kept as low as possible in order to increase the bulk of the crop.

"But to improve starch percentage and DM cut plants just before the first node because there is no nutritive value in the bottom 10cm of the plant," he says.


&#8226 Harvest the crop at about 30% DM.

&#8226 Assess plant DM using thumbnail, milkline and/or oven test.

&#8226 To improve starch percentage and DM cut plant just before first node.

Use the thumbnail test to determine harvest date. Grains at the top of the cob should have a soft cheese consistency and at the bottom be like hard cheese.