vital to drill at right time for later health
Correct timing and depth of sowing into the right seedbed are key factors in establishing a healthy maize crop. Jonathan Riley reports
SOIL temperature is the key factor in deciding when to plant maize.
The crop has a relatively high minimum temperature requirement for growth and fails to germinate until the soil temperature is 8C.
Data from Maize Growers Association trials, at four sites across the country, have shown that starch content of the harvested plant is related to an optimum window for drilling dates. Both drilling too early as well as too late left lower starch yields. Highest starch yields were recorded in crops drilled between April 13 and May 1.
"Late drilling will delay the final maturity of the crops and reduce dry matter yields. Drilling too early exposes seeds to colder temperatures or causes losses through the seed rotting in the soil before germination has occurred," says MGA agronomist Simon Draper.
Generally the required temperature will be reached during the last 10 days of April and the first week of May.
In south facing fields, or in fields that have been ploughed or received slurry applications, warming will occur more quickly.
"Maize needs a minimum soil temperature of 10C to germinate," says Mr Draper. "As soon as 8C is measured drilling should start.
"But, bear the date in mind. If it is early April then it may be best to wait for three to four consecutive days at 8C. If it gets to mid-April, drill as soon as 8C is reached," he says.
Mr Draper advises measuring temperatures using a garden thermometer at a depth of about 100mm (1.5in). Also ensure soil is sealed around the thermometer when it is replaced or subsequent temperature readings may be affected, he adds.
"On heavier soils there is a greater risk of seeds rotting before germination so it may be advisable to drill when soil temperatures are sustained at 8C for three consecutive days. On lighter soils 8C is sufficient as the risk of seed rotting is minimal while the soil temperature climbs from 8C to 10C at 100mm depth," says Mr Draper.
Advised drilling depths range from 2.5cm to 12.5cm (1in to 5in) depending mainly on soil moisture availability.
Depths should be at the minimum level required to get good germination – normal depth suggested is 5cm to 7.5cm (2in to 3in).
"Heavy soils hold moisture well and drilling at about 1in to 2in is acceptable," says Mr Draper.
At a cold site, the nearer the surface, the quicker germination will occur. But on lighter soils where the soil surface is prone to drying out, deeper planting is necessary so that the germinating seed has enough moisture.
Deeper drilling is also necessary where bird damage is particularly prevalent.
"Crops can be drilled at depths of 5in but this will delay crop emergence, weakening the plant and reducing germination rates," says Mr Draper. *
MGA agronomist Simon Draper: "Late drilling delays crop maturity."