SOWING DATE

Stage TWO: RE-SEEDING

Choosing The Correct Seed Mixture

No single grass variety has all the desired agronomic traits and a grass seed mix can address this. When it comes to selecting the correct seed mixture, the Pasture Profit Index (PPI) is essential to reference specific characteristics and values within the pasture.

• Diploid: Tetraploid proportion; • For grazing: 50% diploid: 50% tetraploid (reduce tetraploid % on difficult soils); • For silage: 60% diploid: 40% tetraploid (narrow range in heading dates are advised); • Clover inclusions should also be considered (now a requirement for derogation farms considering reseeding).

Diploids Vs. Tetraploids

The main difference between diploids and tetraploids is the number of chromosomes per cell in the grass plant. Diploids have two sets of chromosomes per cell while tetraploids have four.

Diploids have tended to dominate mixtures in Ireland in recent years but tetraploid varieties are a key component of modern grass seed mixtures.

Because of the extra chromosomes, tetraploids have a bigger cell size and have a higher ratio of cell contents (soluble carbohydrates) to cell wall (fibre), indicating that they have a higher water content per cell. Diploids have more tillers per plant and, due to the lower water content per cell, have a higher DM/kg of feed and more energy than tetraploid plants. Both varieties have similar protein levels.

Tetraploids are more palatable to livestock, leading to higher intake, and are more drought tolerant. However, their higher water content goes hand in hand with a lower DM compared to diploids.

On heavy soils subject to poaching, the persistence of tetraploids may suffer, while seeding rates for tetraploid grasses will need to be higher because of the larger seed size.

Ideally, seed mixtures should have less than a seven days’ range in heading dates between cultivars. In a silage mix, high overall DM production and density are the key targets.

Silage mixes should not be used where swards are used mainly for grazing. A small range in heading dates (e.g. seven to 10 days) is preferable to shortening the heading period. All varieties will head, however, some have a greater tendency to head and continue to re-head, which is not desirable in a grazing sward.

HEADING DATES

EARLYS

Head out during the first half of May

INTERMEDIATES Head out during the second half of May

LATES

Head out during the first half of June

Benefits of mixed grass / white clover swards

Animal

• Increased dry matter intake

+ 1.5kg DM/cow/day

• Increased milk solids production

+ 30kg MS/cow/year

Sward

• Increased dry matter production

+ 800kg DM/ha

• Potential to reduce nitrogen fertiliser

with white clover contents >25%

• Increase farm profit by €150/ha

• Dry matter intake • Feed quality • Animal performance • Total grass growth

Economics

• Nitrogen use