Suitable both as food for humans and as livestock feed, sorghum thrives even in an increasingly dry climate. Agroscope has developed maps showing the potential growing areas for silage- and grain sorghum.
Sorghum bicolor (L.) Moench, also called ‘great millet’, originated in Africa. Nowadays it is cultivated throughout the world, with about 95% of production stemming from Africa, America and Asia. In Europe, France and Italy in particular are important producer countries. In Switzerland, however, the total area devoted to sorghum cultivation is less than 350 ha – this despite the potential cultivation areas being disproportionately larger. With a view to the possible expansion of sorghum cultivation, we looked at which areas of Swiss arable land would be suitable for growing silage sorghum or grain sorghum, based on the plant’s heat requirements.
Different warmth requirements for silage and grain sorghum
We derived the necessary key figures regarding the thermal requirements of silage- and grain sorghum from information in the literature and Agroscope’s trials at its Reckenholz site. The experiments with grain sorghum took place from 2009 to 2011, those with silage sorghum from 2018 to 2022. The results of the trials show that with an early-May sowing and the choice of a base temperature of 8 °C, silage sorghum requires an accumulated temperature of around 1150 °C to ripen, whilst grain sorghum requires an accumulated temperature of around 1350 °C.
Silage sorghum could be grown on all of the arable land
The regional evaluation of accumulated temperatures based on grid data of the Federal Office for Meteorology and Climatology for 2001–2020 showed that practically all of the arable land available today is suitable for growing silage sorghum (Fig. 1). According to our estimates, maturity would occur almost every year between mid-August and late September, with a delay of about one week in the case of a later mid-May sowing.
Favourable land for cultivating grain sorghum is limited
For grain sorghum, however, the probability of maturity being reached before the end of October rapidly decreases with increasing altitude. Very-favourable-to-favourable areas are limited to locations below about 550 m.a.s.l.
- Accumulated-temperature maps show that the thermal requirements for the cultivation of silage sorghum are already met on most of the arable land in Switzerland.
- Favourable areas for the growth of grain sorghum can be found in low-lying regions along the Lake Geneva–Lake Constance axis, as well as in the Valais, the Rhine Valley and south of the Alps.
- With a late sowing, there is an increased risk of grain sorghum only achieving maturity towards the end of the year, if at all.
- The breeding and introduction of early-maturing sorghum varieties can support the cultivation of grain sorghum in Switzerland.