Maize is one of the most important crops in Switzerland. Variety selection and site adaptation play a crucial role in maize cultivation in a changing climate. Heat-supply maps created by Agroscope help in the choice of suitable varieties.
Maize is one of the most important annual crops. In Switzerland, silage-maize and green-maize cultivation account for around 17% of arable-land use; grain maize accounts for a further 6%. Because of its subtropical origin, Maize requires a relatively warm climate for its development, with temperature requirements differing depending on variety. Knowledge of both the average available accumulated temperatures over several years at a site as well as their variability from year to year can support the choice of varieties and the assessment of the risk of incomplete maturation.
Mapping the Accumulated Temperatures
Accumulated temperature maps for early, mid-early and mid-late maturing silage and grain maize were created based on the gridded data of the Swiss Federal Office for Meteorology and Climatology for the years 2000–2019. For the calculation, 1st May was assumed as an average sowing date and temperatures were cumulated from this date until 15th October. The accumulated temperatures calculated over this period were compared with the demands of various maturity categories. This enabled the designation of favourable acreage in current farmland for the cultivation of early, mid-early and mid-late maturing silage- and grain maize.
The results show that silage maize can be cultivated on around 70% (mid-late maturing varieties) up to around 90% (early-maturing varieties) of current farmland. For grain maize, the percentages of favourable acreage are lower: 30% of current farmland for mid-late maturing varieties, and around 60% for early-maturing varieties. The maps show that Ticino, Central and Lower Valais, the Lake Geneva Region up to the Bernese Seeland, Basel-Country, the Rhine Valley from Chur downwards and the Lake Constance Region as well as the riverscapes in the Aare, Reuss and Limmat triangle are favourable areas for the cultivation of grain maize in terms of temperature.
Variability of Accumulated Temperatures and Future Development
A similar analysis was also conducted based on daily data from 14 weather stations. All of the stations were located at altitudes under 600 m.a.s.l., and were chosen so as to cover all of the farmland. With few exceptions – Aadorf/Tänikon in Eastern Switzerland and Fahy in the Ajoie – the results show that all sites are suitable for the cultivation of silage maize, even mid-late maturing varieties. However, at around half of the sites, temperatures are unfavourable for the cultivation of mid-early and mid-late maturing grain-maize varieties in more than one year in three. With climate change, temperatures are expected to continue rising. Maize cultivation could benefit from this in two respects: one the one hand, from a bigger window for sowing because of the rise in spring temperatures; on the other, from more opportunities for the cultivation of late-maturing varieties. Climate change does not only entail advantages, however; previous Agroscope studies concluded that increasing heat and drought stress could have adverse effects on maize cultivation in the medium-term.
- Maps of accumulated temperatures offer an easily interpretable basis for the choice of varieties in maize cultivation. Information provided in this manner can usefully supplement the Lists of Recommended Maize Varieties.
- The accumulated-temperature evaluations for 2000–2019 show that with current climate conditions, mid-late maturing silage maize and grain maize can be cultivated on 70% and 30% of farmland, respectively, without major risk of incomplete maturation.
- The maps highlight the climatically highly favourable sites in Ticino, the Valais, Western Switzerland and the flood plains of the Aare, Reuss, Limmat and Rhine, where mid-late maturing varieties of grain maize can also be cultivated.