Maize yield will fall by 22kg of dry matter per hectare for every 1mm of soil moisture deficit.
That was the message from Allister Holmes when he spoke of the drivers for maize yield at the CROPS 2014 expo last week.
Maize had deep roots, up to 1.8m, but inadequate moisture at any growth stage could reduce the yield, said Mr Holmes, who is research and extension team leader for the Foundation for Arable Research in Waikato.
Too much moisture was also a problem.
''Maize doesn't like wet feet. If there is water pooling early in the season, it won't recover.''
Waterlogged soils could reduce the plant's ability to take up nutrients, and create a toxic soil environment. Prolonged waterlogging could cause large reductions in maize yields.
The highest maize yields were achieved in northern New Zealand, because of the high radiation and long growing season.
In Gisborne, the seeding rate for maize could be 75,000 seeds per hectare, but the crop at the FAR's Chertsey site was sown at 105,000 seeds per hectare and up to 120,000 seeds per hectare. Final populations would be about 5% lower.
Hybrid maize had changed a lot, Mr Holmes said. Twenty years ago the hybrids were North American but today many came from Europe and were better and more vigorous in cool seasons.
Severe weed infestation could greatly reduce maize yield, make harvest difficult and contaminate silage, and pests such as the Argentine stem weevil, greasy cutworm and black beetle could be a problem.
Birds could do much damage by killing maize seedlings while digging for the seed.