Maximising grassland yields: 3 stages to great grass

Currently only 7% of the land area on specialist dairy farms in Ireland is reseeded annually (2.5% nationally if we look at the entire grassland area).

Why consider reseeding this spring?

Increasing the proportion of the farm reseeded increases total and seasonal dry matter (DM) production. When accompanied by an increased stocking rate, it leads to increased herbage utilisation and has positive effects on profitability.

Economically, a low proportion of perennial ryegrass in the sward is costing dairy farmers up to €300/ha in lost grass production during the growing season.

Reseeding pasture should be looked at as a long-term investment, with newly reseeded swards typically lasting for at least 8-10 years. The ultimate aim is to reseed 10% of the milking platform annually, resulting in a completely renewed platform every 10 years.

Current grassland management figures highlight that every extra tonne of grass utilised is worth an additional €173 to the farm.

Re-seeding this spring will result in:

Improved sward quality (DMD);
Increased animal performance;
Increased DM yield;
Higher spring and autumn growth;
Rapid regrowth in April;
Improved response to nitrogen (N) fertiliser;
Increased farm profitability.

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.

Soil fertility

Target turnaround time to get a reseed back into production should be 60 days.

Generally, decisions around reseeding are negative due to the view that paddocks are out of production for too long. The time that the sward is out of production can be minimised by cultivating seven to 10 days after spraying off the old grass – a major failing at farm level is to wait too long after spray off.

When spraying off paddocks for stitching in – let the grass cover grow to 400-500-600kg DM/ha before spraying off. This is due to avoiding old grass coming back into the sward.

The paddock/field for reseeding should be sprayed off with a high-quality glyphosate product in order to kill off any existing vegetation present.

Where ploughing, without spraying off it is common for weed grasses to regrow quickly and are then very hard to control. Where minimum cultivation is being practiced the vegetation needs to be either grazed off or topped to allow a cleaner surface with little trash as possible.

2. Re-seeding

Target turnaround time to get a reseed back into production should be 60 days.

There are two main methods of reseeding; conventional and minimum cultivation. Conventional is using a plough and minimum cultivation techniques are carried out without a plough, most commonly direct drilling and power harrowing.

Ploughing

Once the vegetation has died off about seven to 10 days after spraying the field is ready for ploughing; during ploughing any trash on the surface is buried. After ploughing it is time to spread lime and fertiliser based on the soil sample results;
Surface is then power harrowed to produce a fine, firm and level seed bed which will give the optimal conditions for sowing;
In order to achieve a firm seed bed the field should be rolled before sowing;
Avoid having a fluffy seed bed as this will cause the grass seed to go too deep into the soil and lead to poor germination/establishment;
Weather permitting the reseed should be rolled again in an opposite direction to compress the seedbed and increase seed/soil contact.

Direct drilling

An existing sward needs to be sprayed off as well as grazed tightly or topped after being sprayed off;
Some direct drills place seeds in a slit 2-5cm apart; others rotavate a 4cm slot and place in both seed and fertiliser. Both work very well but it is recommended to do an additional run over the field in a diagonal direction.

Power Harrow

Involves using a power harrow to cultivate soil surface to a depth of 2-3in;
Ideally, the field should be harrowed three times in different directions to ensure a fine tilt and to break up old sods sufficiently;
After harrowing, the field should be rolled before seeding to ensure seedbed is firm;
Seeding should then take place with the seed being placed on the soil rather than deep in the soil;
The field should then be rolled again in the opposite direction to optimise soil/seed contact.

3. Post-emergence

It takes about 11 months for a new sward to fully establish; therefore, the management of the reseed in this period is important.

Graze the new reseed as soon as the plants do not pull out of the ground (pulling test), at a cover of approximately 700–1,000kg DM/ha;
Historically, first grazing does were completed by youngstock/calves; however, where ground conditions allow, graze with the main grazing herd to move through the cover more rapidly;
For the next few grazings, frequent light grazings (≤1,400kg DM/ha) are advisable;
Avoid cutting for silage in the first year of establishment.

Weed control

Post emergence spray should be applied five to eight weeks after reseeding

Teagasc research indicates that a paddock capable of producing 10t DM/ha, with a 1t infestation of docks, will reduce yields of grass DM by 10%.

Therefore, a typical paddock growing 10t DM/ha/year with a 40% infestation of docks, will grow 6t DM/ha and 4t DM/ha of docks – resulting in a 40% reduction on the grass DM yield potential of that paddock.

Use appropriate spray, clover safe or non clover safe.

You can browse the 2020 Grass and Forage Seed Brochure here