Farm Ireland
Independent.ie

Thursday 22 February 2018

Meeting the drought challenge

Mary Kinston

More farms have succumbed to drought after another week of warm weather and a weekend of scorching temperatures. This article sets out the management practices required for such conditions.

Soils have become progressively drier and pasture growth rates are falling, with more farmers now recording growth rates of less than 20kgDM/ha/day.

It seems clear that this phase of dry weather will now have a widespread impact on farms and will take time to resolve even when the rain finally arrives.

Farmers need to review their situation at least once a week as the length of this dry period will determine the magnitude of the changes required.

* Extend rotation

As soon as it is obvious that pasture growth rates are declining, the solution is to extend the rotation length from around 20 days (1/20th of the farm) to 30 days (1/30th) to reduce the amount of area grazed each day by the herd.

Lengthening the rotation to 30 days has two positive effects. By reducing the amount of pasture eaten on a daily basis, the limited supply of grass is extended. Secondly, it allows each paddock more time for recovery and re-growth.

* Fertiliser

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A number of farmers have questioned the use of nitrogen fertiliser in dry conditions. While the application of nitrogen is important in summer to promote high quality pasture, tillering and ryegrass persistence, it needs to be applied before the soil moisture is limiting grass growth.

Remember that water, which is involved in plant transpiration, provides soil nutrients in solution.

When water deficit reaches a critical stage, transpiration is reduced and, accordingly, grass growth slows.

As a result, soil nutrient uptake is restricted and application of fertiliser does not alleviate the nutrient shortfall since there is little moisture other than dew to wash in the fertiliser and hold nutrients in soil solution.

Therefore, when the farm is too dry there's no point applying fertiliser until 25mm of rain has fallen.

It's interesting to note that 1t/ha of grass dry matter requires 200-250t/ha of water absorbed by the roots and transpired through the grass foliage into the atmosphere.

This corresponds to a depth of water of 25mm/ha whether taken up from soil reserves or falling as rainfall.

However, once the 25mm or greater has fallen, although there is a considerable pool of nitrogen already in the soil, land will respond to nitrogen fertiliser.

Applying 30-40units of nitrogen fertiliser after rain, will give pasture plants immediate access to some N, while the soil processes recover with improved moisture levels.

Continue to hold a grazing rotation of greater than 21 days and ideally 26-30 days once rain is received.

* Supplements

Pasture quality will decline due to an increase in fibre content in a hot dry summer. As a result, both pasture quantity and quality will limit intake and milk production.

However, to get high responses to supplement, it's firstly imperative that the available pasture is eaten and not wasted. Leaving poor grazing residuals of more than 4cm will only reduce pasture quality further, and will rot away once rain is received.

It is easy to underestimate the amount of pasture dry matter available, as there is more dry matter at the same height than at other times of the year.

Secondly, a high response to supplement will only be achieved on cows that do not have to be dried off and can be milked to the end of lactation (eg, greater than 260 days in milk).

Be clear that feeding supplements to cows that will be culled because they are empty, lame or have a high SCC is not the wisest of moves.

Use your records and consider an early scan to determine which cows need to be culled or dried off early (eg, first lactation).

This will allow you to provide more grass and supplement to the cows that can milk for the remainder of the season.

As one farmer said to me recently: "2013 is a year to tidy up the herd; no passengers allowed."

When choosing a supplement, it needs to be primarily high energy content and secondly 16pc crude protein to support mid-lactation.

If high levels of concentrate feeding is required consider the use of a nut over a coarse mix, and provide the cows with ample water.

* Animal health

Hot conditions will reduce milk production, with Holstein Friesian cows being more sensitive than crossbreds or Jersey cows.

When air temperature exceeds 23C and relative humidity hits more than 80pc, cows begin to experience heat-induced depression of feed intake and lower productivity.

Cows are at risk of heat stress and out of their comfort zone when day time temperatures exceed 27C and night time exceeds 15C. To reduce the impact of hot conditions on cows:

* Provide plenty of water. Lactating cows require more than 100litres/day and drink between two and six times at day;

* Provide supplementary feed in the form of silage at night to reduce impact of heat produced by rumen fermentation;

* Use paddocks with shade in really hot conditions;

* Reduce walking distances and time spent in holding yards and handling, and milk later in the afternoon when it's cooler.

Mary Kinston is a discussion group facilitator and consultant, and farms with her husband in Co Kerry. She can be contacted at mary.kinston@gmail.com

Irish Independent