Any ryegrass species may be available in either tetraploid or diploid varieties. The ‘ploidy’ characteristics arise because tetraploid plants have four sets of chromosomes, while diploid plants have two. As a result, tetraploid plants have larger cells, a higher ratio of soluble carbohydrates (sugars) to cell wall (fibre) and a higher water content. Diploid plants have thinner leaves, are more densely tillered and have smaller seeds than tetraploids. This means they can be sown at a lower rate per hectare to achieve the same plant density as tetraploids.
Diploids can be grazed hard and recover quickly from hard grazing. They can be allowed to grow past 15cm and will be less likely to lodge than tetraploids. This makes diploids a good choice for farms where there is less focus on precise grazing management.
Tetraploids have a higher water soluble carbohydrates (sugars) in their leaves which means that livestock will prefer tetraploids, particularly in winter and early spring. They should not be grazed lower than 5cm in height as their larger leaves take longer to recover. The heavier leaves also increase the tendency to lodge, so if grazed, they should not be allowed to grow higher than 15cm. Once tetraploids go to head they lose their forage quality quicker than diploids due to the extra fibre needed in stems to hold up the heavier seed.
Choose diploids for hay
At heading, diploids maintain their forage quality better than a tetraploid. This is because they need less fibre in the stem to hold up the lighter seed. This makes diploids the best choice for hay.
Choose tetraploids for silage
The higher sugar content makes tetraploids ideal for silage, which requires larger amounts of sugars for fermentation.