• Which form of nitrogen is best for grain varieties, and which for silage varieties?
  • What row spacing is best for sowing sorghum? How deep?
  • Sorghum has significantly lower water requirements than corn. There is still potential to increase the area under this crop. 

Much lower water requirements than corn

At the RAGT Field Days and Corn event in Bolesław, in the south of Opole Voivodeship, considerable attention was devoted to sorghum cultivation. This crop’s area in our country is still negligible. Its area exceeds 14 thousand hectares by a little, which is only 0,7 - 0,8 percent of the corn area in Poland. Nevertheless, it has the major advantage of having significantly lower water requirements. Experts sometimes say that 30 - 40 percent of the water corn would need is enough for sorghum. Even under less optimistic assumptions, 50 percent of the amount of water required for corn meets sorghum’s needs. 

Sorghum in three forms

Sorghum is available in three forms. The tallest varieties are those intended for biogas and silage. These forms can reach a height of up to 3 - 4 m. The next type of sorghum is an intermediate form—varieties intended strictly for silage. These varieties reach a height of approximately 2 - 2,5 m. Grain sorghum is the shortest, with plants reaching approximately 1,2 m. 

- The shortest grain sorghum has three dwarfing genes. If a few individual taller plants appear, this is a disruption of one of the genes. There may be various causes—for example, cold or a reaction to herbicides - explained Robert Grzyb of RAGT.  He pointed out that sorghum is an answer to the changing climate, drought and poor growing conditions, and that the sorghum market in Europe is growing.

What yield per hectare? Which form of nitrogen should be chosen for sorghum?

- Of course, sorghum can be sown on better soils. Some farmers decide to do so. They achieve a grain yield of 8 - 10 t / ha there. But let’s be realistic: if sorghum is planted on class 5 - 6 soil, then a yield of 5 -7 t /ha is already very good - the expert emphasized.

- For silage varieties, nitrogen fertilization requirements are higher because the plant has to produce more biomass. But this is roughly half of what is applied to maize. Nitrogen can certainly also be applied in forms such as farmyard manure or slurry. A good form of nitrogen for sorghum is calcium ammonium nitrate, or alternatively UAN. Let’s try to avoid urea. Of course, it is permitted, but mainly for silage crops. When fertilizing sorghum for grain, it can delay vegetation and ripening - he explained.

Sowing sorghum. When and at what spacing?

In Poland, we start sowing between 10 and 15 May, so that emerging plants can avoid the so-called Cold Zośka. Frosts of around -2 C can damage seedlings.

- In Poland, you need to sow the earliest varieties possible - Robert Grzyb pointed out. - We sow at a depth of 2-3 cm. Sowing with precision seed drills at a row spacing of 45 cm is quite common. We do not have very many herbicides for sorghum, and it is important for the plants to thicken up and cover the soil as quickly as possible. In the USA, sowing is often done at a spacing of 75 cm, but there are more herbicides for weed control in sorghum there.

- Sowing works with beet plates. A beet plate has 36 holes, while plates specifically for sorghum have 72 holes. But you can also sow with grain drills, added the speaker from RAGT. It is very important to maintain a uniform sowing depth. The recommended sorghum plant population is 280 -300 thousand seeds / ha.

What about weeds in sorghum?

For weed control, we can use pendimethalin, dicamba, and glyphosate. No other active substance is registered for herbicidal protection of sorghum in Poland. Soil-applied treatments are the most effective. Unfortunately, s-metolachlor is no longer available for weed control (it was not registered in Poland, but there were European registrations). Trials indicate that combinations incorporating, among others, clomazone or mesotrione are effective for weed control in sorghum. The most troublesome weed in sorghum is barnyardgrass, and controlling it is considered a priority in herbicidal protection. Insecticides are usually not needed, and fungicides are not applied either. 

Under Polish conditions, sorghum does not dry down to a moisture level that would make drying unnecessary. However, harvesting can begin at a moisture level of around 20 percent. Because the grain is denser, reducing its moisture takes slightly longer than in the case of maize.