This section provides a guide on how location and management factors
are accounted for when choosing forage maize varieties.
Ontario
Heat Units (OHU)
This is a standard system of assessing growing conditions
by accumulating maximum and minimum air temperatures of above 10ºC in the daytime and 5ºC at night,
from 1 May to 31 October.
Harvest year |
OHU 1 May - 31 Oct |
Trial sites |
|
2001
|
2393
|
Maryland
|
|
2002
|
2100
|
Maryland
|
|
2003
|
2338
|
Maryland & Comber
|
|
2004
|
2385
|
Gransha & Comber
|
|
2005
|
2303
|
Gransha & Comber
|
|
2006
|
2632
|
Gransha & Comber
|
|
10yr Mean
|
2359
|
Average of 1997-2006
|
Varieties
differ in the amount of heat energy they require to reach 30% Dry Matter (DM), but around 2300-2400
OHU is normally
required for an average-maturing variety grown in the open system. If a plastic mulch is used, this
requirement falls to around 2100 OHU, due to the heating effects of the plastic. These trial sites are
broadly of ‘average to good’ for maize growing. (Gransha & Maryland are trial sites close to the
Plant Testing Station,
Crossnacreevy)
Key characteristics
Growing
maize successfully in Northern Ireland involves selecting varieties with the correct balance between
the ability to fully mature under conditions that are seldom ideal and yet not over sacrificing performance
potential. Clearly, only varieties with sufficient stress tolerance are able to deliver good yield,
quality and energy outputs under these conditions, but the varieties that are least demanding of growing
conditions are generally among the lower yielding varieties.
Finding the
correctly balanced variety to meet each growers needs, depends on how generally suitable is the growing
area and how good are the specific fields to be used, on whether or not plastic cover is being used
and whether starch content or total energy output is the more important factor.
General
principles
The dry matter content of the harvested crop should not
be less than 25% as, below this level, effluent problems become an increasing risk. While it must always
be realised that years can differ dramatically, if previous crops have failed to achieve this 25% target
level, then earlier maturing varieties than before, should be selected.
Conversely,
maturing a crop beyond 35% dry matter and certainly over 40% is not advised, as there are no apparent
animal performance benefits and utilization and ensiling problems can occur. If previous crops have
either become too dry or have had to be harvested too early in the autumn, and this pattern has been
repeated for several years, then selecting a later maturing variety should provide higher yields from
a crop that is still between the 25-35% DM range.
Specific
requirements
- If plastic cover is being used this will advance
the maturity of the crop and will allow later silking, higher yielding varieties to be used than would
be possible if growing an open established crop. Therefore, the key characteristics for selecting varieties
under plastic are their starch; ME and total dry matter yield potentials.
- If growing
maize in open establishment, then the crop has no protection from the ambient conditions and unless
in a very favourable growing area, dry matter content (DM%) ranking is an important characteristic as
this identifies the risk of not getting a fully matured crop under restricted growing conditions, particularly
if it proves to be a poor season.
- If high starch content is an important criteria
for the winter diets, then any variety compromises should be made in favour of earlier maturity and
higher DM%, as this will represent less risk of getting a disappointing starch content if growing conditions
are unseasonably poor.
- If high total energy (ME) content is an important criteria
for the winter diets, then any variety compromises should be made in favour of later maturity and higher
total yield. The key limitation is ensuring that the variety chosen is still capable of achieving the
25% DM threshold within the constraints of the location and management system involved.
In
general, the earliest maturing, lowest yielding varieties normally require the least energy and will
be ready for harvest first. They may also tolerate poor growing seasons better, but will not have as
high a yield potential as the later maturing varieties.
Expert
guidance on variety decisions is available to growers from the Department of Agriculture and Rural Development
(DARD), Agricultural Development Centres.
Merchants and plant breeders
requiring more specific scientific
and technical information should contact Trevor Gilliland, AFBI-Crossnacreevy at:
info@afbini.gov.uk
