In terms of extending rotation length and building farm cover, decisions taken now will have a major impact on grass supply to the end of this year and into next spring.

The Teagasc PastureBaseIreland grassland database has recorded an average national grass growth rate of 75kg DM/ha/day on dairy farms around the country during the last week. Good growth has been based on high soil temperatures (18° to 20°C), adequate soil moisture and increased soil N availability.

On many farms, winter feed stocks are extremely tight and so the unseasonably high current growth rates provide an ideal opportunity to make additional winter feed.

While growth rates are exceptionally high on many farms this week and surpluses will be harvested, this should not be achieved at the expense of autumn farm cover targets which are critical to extending the grazing season and reducing winter feed requirements.

So what are the

rotation length and

farm cover targets?

Successfully extending the grazing season requires that every farm creates and sticks closely to an autumn grassland plan based on the feed demand (overall stocking rate) and growth capacity of the farm.

Figure 1 outlines the target average farm cover targets for the low (below 2.5 cows/ha) and high (3.3 cows/ha) stocked farmlets within the Curtins stocking rate experiment from now to the end of the year.

At normal stocking rates (2.5 cows/ha), rotation length should be extended by two days per week from mid-August to reach a peak farm cover of 1,150 to 1,200kg DM in early October and the closing farm cover of 550kg DM/ha at housing in late November.

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At higher stocking rates, rotation length should be extended from the beginning of August to reach a peak farm cover of 1,250 to 1,300kg DM in early October and a closing farm cover of 650kg DM/ha at housing in mid to late November.

Between 15% and 20% of annual grass DM production occurs between September and mid-November, regardless of sward type and location. Where farm cover is below target, increased fertilizer application rates during September can efficiently increase grass growth on farms below target cover.

As average farm cover increases, autumn pre-grazing herbage mass will increase but should be maintained below 2,000kg DM/ha until mid-September to ensure maximum grass utilisation and herbage quality.

Swards should be tightly grazed to 3.5cm to ensure that sward quality is not unduly compromised during the longer autumn rotations. Grazing swards tightly during autumn will ensure that light can penetrate to the base of the sward to promote new tiller development.

What if the farm

cover is exceeding the targets for August?

Given that current growth rates are high, it is likely that average farm covers will exceed target levels over the next 10 days.

While August is generally considered too late to harvest heavy silage crops, this year many farmers will make second cut silage in August to reduce winter feed deficits.

In this situation, surpluses should be removed quickly while the base of the sward remains green to maximise regrowth rates.

In as much as possible, farmers should avoid making silage after mid-August as regrowth rates on this area will be dramatically reduced, making the build-up of overall farm cover during September difficult to achieve.

The current high soil temperatures will allow increased autumn nitrogen mineralisation and so lower stocked farms, where sufficient winter feed has already been harvested, should take advantage of the excellent growing conditions and reduce August fertilizer application rates and on-farm costs.

LESSONS FROM JULY DROUGHT

Drought management is not commonplace in Ireland and so it’s important to learn lessons from our experiences of the recent drought during July.

At Curtins farm, all dairy cows were supplemented with 48kg DM of silage and 65kg DM of concentrate over an 11-day period to extend rotation length to 45 days during the drought.

With the benefits of hindsight and from a financial perspective, it would have been preferable to maintain rotation length at 21 days during a period of drought and reduce overall farm cover to below 400kg DM per hectare before supplementation begins.

On many farms, supplementation increased quickly in response to low pasture growth rates, and grazing pressure and pasture utilisation were dramatically and unnecessarily reduced.

It would have been preferable and more financially sensible to begin supplementation to extend rotation length quickly after all remaining pasture had been fully utilised or after the rain had arrived.