A common feature on farms is that historically rented or leased land has been reseeded and the home grazing platform has been excluded. In the coming years, reseeding needs to focus on the grazing platform.
All farming enterprises would like to have swards that last for as long as possible. All farmers in all enterprises need to identify their poorer performing pastures and phase in an action plan to improve their performance. This aspect of grassland management is as important to beef and sheep as it is to dairying.
The risk of poaching increases with the length of the grazing season, particularly during wet periods that often occur in early spring and autumn.
Recent research from Moorepark investigating both wetter and drier soils has shown that in a free-draining soil, dry matter (DM) yield was reduced by 30pc in badly poached paddocks after damage but cumulative DM yield was not altered between undamaged and badly poached areas (see Table 1).
In a heavy soil, annual DM yield was reduced by 14-49pc, depending on frequency of poaching and timing.
A predominantly perennial ryegrass (PRG) sward on a free-draining soil is resilient to heavy treading damage but a PRG sward on wet soil needs careful management to avoid significant losses in DM production after poaching damage.
With more variable weather patterns, the grazing management approach applied needs to be flexible.
The pie charts below show the main reseeding methods employed at farm level from a major grassland survey in the past couple of years.
Ploughing is still a popular method of reseeding. However, minimal cultivation techniques do have their advantages due to topography and stone issues on farms. When farmers were asked how they have sown grass seed, a lot of farmers replied that they did this part of the reseeding process themselves to keep contractor costs to a minimum. It is likely that minimal cultivation techniques will become even more popular in the future.
CONVENTIONAL RESEEDING (PLOUGHING)
Ploughing helps the drainage of the soil profile, but involves a lot more cultivation passes in the reseeding process. It provides the basis for a sound seedbed and a more level surface.
Deep ploughing is only wasted time, diesel and parts, as too many important soil nutrients are buried too deep. As with all methods, after ploughing the objective is to develop a fine, firm and level seedbed. If the tilt is too rough, grass seed will be lost too deep into the soil and will not be able to germinate.
Most minimal cultivation techniques involve spraying the existing vegetation. The seedbed is then prepared using shallow cultivation equipment.
Soil disturbance is minimised so the more fertile soil remains at ground level for use by the young seedlings as well as giving better support for machinery and animals at the early stages of pasture establishment.
This is a fast and simple method of reseeding. If minimum cultivation techniques are to be used it is important that the sward is grazed tightly pre-cultivation.
This method does not bury surface trash, and the remaining dead organic matter releases organic acids as it decays.
This can inhibit seed germination. Applying about 2t/ac of lime before cultivation will help neutralise this effect. More weeds also appear with minimum cultivations, which makes the use of post-emergence spray even more critical.
A number of reseeding methods were compared in Moorepark. These included: a control plot of permanent pasture; ploughing, levelling and one-pass; one-pass; direct-drill; disking and one-pass.
All swards, except the control, were initially sprayed with glyphosate (such as Round-up) in mid-April. Cultivation of the areas took place on May 7 and the initial grazing on July 2.
DM production was measured throughout the year before the plots were sprayed off and after cultivation to calculate the cumulative DM production for the year.
Grass DM production for the treatments are presented in Table 2, right.
These results clearly show that although the reseeded areas were out of production for almost three months their annual dry matter production was similar, if not greater than the control area which was accessible for the entire year.
In the year following reseeding the difference in grass DM production ranged from 13 to 27pc greater, depending on the reseeding methods.
The target turnaround time in which to get a reseed back into production should be less than 60 days.
Generally, farmers are slow to reseed pastures because they 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 the old grass off. In contrast, too many farmers wait too long after spray off.
The best time to control docks and all other weeds is after reseeding. Using a post-emergence spray, seedling weeds can be destroyed before they properly develop and establish root stocks.
Established weeds can seriously reduce the yield potential and economic lifetime of the reseeded sward.
To ensure that a post-emergence spray can be applied, reseeding should be targeted for the spring when establishment conditions are much more suitable and the opportunity for weed control is guaranteed.
The post-emergence spray should be applied approximately five-to-six weeks after establishment but before the first grazing takes place. Ideally, this is when the grass is at the two-leaf stage.
GRAZING MANAGEMENT OF RESEEDED SWARDS
Care needs to be taken when grazing newly reseeded swards. The sward should be grazed as soon as the new grass plants' roots are strong enough to stay anchored in the ground when pulled during grazing.
Early grazing is important to allow light to the base of the plant to encourage tillering. Light grazing by animals such as calves, weanlings or sheep is preferred as ground conditions may still be somewhat fragile, depending on the establishment method used.
Grazing new reseeds with larger animals can create high levels of tiller pulling. The first grazing of a new reseed can be completed at pre-grazing yields of 600-1,000kg DM/ha.
Frequent grazing of the reseeds at 1,400kg DM/ha over the first year will have a beneficial effect on the sward. The aim is to produce a uniform, well-tillered sward.
Particular care is needed during periods of wet weather as damage to newly established swards can have long-term detrimental consequences as it gives weed grasses an opportunity to invade.
If possible, newly reseeded swards should not be closed for silage in their first year of production as the shading effect of heavy covers of grass will inhibit tillering of the new grass plants.
Michael O'Donovan is a Teagasc researcher in the grassland science department in Moorepark, Fermoy, Co Cork