23. Warm-weather Crops: Forage Maize
DH Lister and S Subak

Total area of forage maize in the UK

Specific Indicator
Maize produces more forage than ryegrass in warm, dry conditions and so may be grown more widely in England & Wales if warm, dry summers become more common. The specific indicator for this potential change is the area of forage maize grown in the UK.
[ Source: Ministry of Agriculture, Fisheries and Food, Foss House, Peaseholm Green, York YO1 2PX]

Relevance
Forage maize is already an important crop, providing about 1.6 million tonnes of dry matter to supplement livestock rations over winter. Silage produced from forage maize is normally grown by individual farm enterprises for 'home' or local consumption, and usually for cattle feed.

Sensitivity to climatic and other factors
Maize has a different mechanism of photosynthesis from all other major crops in the UK (C4 rather than C3) which is most effective at warm temperatures. In an average growing season in the UK, despite rapid advances in plant breeding, maize only just receives sufficient degree-days and solar radiation to produce viable yields. Although the crop is grown commercially on a small scale in many parts of northern England and parts of Scotland, the more favourable growing areas are limited to the warm lowland parts of southern and central England and coastal Wales. The crop is vulnerable to adverse weather conditions in its establishment stages.
The area of maize grown obviously depends on trends in livestock production and the profitability of competing crops as well as climate.

Change over time
Although stable in area throughout the 1980s, the area of forage maize roughly quadrupled through the 1990s. This large expansion is due to a combination of factors, including the introduction of new varieties which are better adapted to UK conditions, perceptions of a warming climate, recent experience of warmer weather and the introduction in 1993 of an arable payment scheme under the Common Agricultural Policy.

The area of maize stabilized in the late 1990s at around 110,000 ha. However, a sudden jump in 2001 took the area to over 120,000 ha and, despite a small reduction in 2002, the area is still above this threshold. In future, the area under production might be expected to increase in a warmer climate, tempered by reduced payments for new producers if the ceiling on area payments is not raised. However, elevated temperatures will favour higher maize yields only so long as there is sufficient soil moisture. A reduction in precipitation of 10% accompanying higher temperatures resulted in lower yields in south and south-east England in simulation experiments. The value of the crop tends to be too low to warrant investment in irrigation. Therefore expansion in production area may be concentrated in the western and northern regions of the UK, which receive higher rainfall but are currently too cool for maize production.