Forage Sorghum – The obvious forage alternative for marginal areas under current economic conditions

Bruce Paterson, agronomist Pannar Seed, KwaZulu-Natal and Cape

Adequate quantities of quality forage are a prerequisite for successful livestock production. Under the current conditions of very high input costs for fuel, fertiliser and some chemicals, there may be a benefit in turning from maize to forage sorghum in certain environments where soil types and temperatures are suitable. Lands that are marginal for maize cultivation can be used for successful forage sorghum production with reduced risk.

Forage sorghum is more drought tolerant than maize, is well adapted to heavier soil types, and seed costs for establishment are low. It is very versatile and can used as foggage, green chop, silage or grazing.

Theft is also not an issue around urban areas and lands can still produce up to 10 to 15 tons of silage on a dry matter basis.

Pannar Forage Sorghum Hybrids
Pannar hybrid forage sorghum is produced by crossing specially selected grain sorghum lines with Sudan grass. There are currently two proven hybrid options commercially available from the Pannar stable of crops. These are PAN 888 or PAN 868.

PAN 888 is an earlier maturing type flowering at 75-80 days if left, with the best regrowth capacity in the package. It is suited to frequent grazing’s or green chop if cut at the correct stage. Grazing should occur between 50cm and 100cm to allow for good regrowth. Early grazings should not be very heavy to allow some reserves for quick regrowth; 20-25cm of leaf should remain.

PAN 868 is the other later maturing option with improved leaf disease tolerance, flowering at about 130 days. This PAN 868 has been specially selected for high sugar or sucrose content (±15% brix). It is best suited to a single early grazing if needed or can then be left for silage or foggage. Plant heights can easily reach 2.8m. For silage, the late milk stage or early dough stage is the best time for cutting. This should have high sugars and protein and will make quality silage, with a dry matter content of close to 30% for best quality silage. To enhance the quality of the silage, either an inoculant or something like molasses powder can be added to increase value of the silage.

Sowing and fertiliser guide
Forage sorghum prefers warmer soil temperatures for germination. Ideally, soil temperatures should be greater than 18 degrees Celsius during the day. In the high-altitude cooler regions, it is advisable to wait until November before sowing to ensure soil temperatures are adequate.

Forage sorghum has similar soil requirements to maize and does not perform well on soils with acid saturations above 18-20% or very low pH (<5). Seed can be planted in rows or with an air seeder or can be broadcast and incorporated into the soil and rolled. Seeding rates are higher when broadcast (15-20 kg/ha), whilst when sowing in the row they may vary from 5 kg/ha to 14 kg/ha depending on the soil potential and planned fertiliser applications.

Fertilisation is very similar to maize; however, the nitrogen can be split and applied after each use (20 to 40 kg N/ha). Phosphorus levels should ideally be about 15 mg/l or greater with sufficient phosphorus applied for any crop removal. If silage is going to be made, some additional potassium should be applied to ensure levels in the soil remain the same. This could be broadcast before planting or applied with a topdressing of nitrogen.

Precautions
Farmers using any forage sorghum hybrid should be aware that under conditions where the plants are under stress from extreme cold, heat or drought, there may be the danger of either prussic acid poisoning or bloat. Sorghum and Sudan grass plants contain a compound called dhurrin, which can break down to release prussic acid (hydrogen cyanide, HCN). Dhurrin content is highest in young plants. Hence it is better to not graze or chop plants until they are about 50 cm tall. A lick supplement with sulphur can assist and reduce the risk of prussic acid poisoning and bloat.

Although plant roots take up nitrogen (N) as both ammonium (NH4+) and nitrate (NO3-) ions, under most soil conditions nitrate dominates. However, under exceptional circumstances (continual cloudy weather and a high nitrogen application), the rate of uptake exceeds the rate of nitrate reduction resulting in an accumulation of nitrate in the plants. Ruminant animals with high nitrate levels in their diets accumulate nitrite (NO2-). Nitrites may accumulate in the animals and in the blood combine with haemoglobin to form methaemoglobin. This is known as nitrate poisoning and is toxic to animals. Animals should be removed for a week or two until conditions return to normal and the crop should not be grazed for some time after topdressing. This should never exceed 70 kg N/ha to be safe.

For more information, please contact Bruce Paterson at 060 970 0717 or bruce.paterson@pannar.co.za or contact you nearest Pannar representative or www.pannar.com.