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28 September 2017

Boosting spring pasture growth will support your summer milking goals.

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Grazed pasture is the most economic form of feed. Provided all the conditions for growth are in place, nitrogen (N) – a growth booster – can increase pasture dry matter at a time of peak demand.

In general, spring pasture response rates will lie somewhere between 10:1 and 20:1. That is, every kilogram of applied nitrogen will grow between 10 and 20 kilograms of dry matter (kg DM) within three to eight weeks of application, says Ballance Science Extension Officer, Josh Verhoek. SustaiN is a good option if between five and 10 millimetres (mm) of rain is unlikely to fall within eight hours of application, as it will help to reduce nitrogen losses from ammonia volatilisation. If a lack of sulphur is likely to limit the effectiveness of nitrogen application, SustaiN Ammo or PhaSedN Quick Start are good alternatives.

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As well as boosting pasture growth, Nitrogen can improve pasture resilience by encouraging tillering. “The more tillers pasture has going into summer, the better its chances of enduring summer grazing, weed invasion and drought, and the quicker it will recover for the next season,” says Josh. Field trials have shown nitrogen application as late as December/January improved shoot numbers by 37 percent – more than double the response achieved using irrigation.1

Nitrogen can also be used to encourage pasture growth beyond immediate demands so it can be harvested as conserved feed to meet a feed deficit later in the season. As long as conditions are good for growth, applying nitrogen before you shut up the hay or silage paddock will improve yield. Applying nitrogen after harvest will improve yield from a second cut or reduce the amount of time the paddock is out of rotation. “Clovers will have been shaded out by the long grass grown for hay or silage, so plants will need an alternative source of nitrogen until the clover recovers and starts fixing atmospheric nitrogen again,” says Josh. “Once again, if the required amount of rain is not on the radar, then SustaiN is preferable to urea. SustaiN K is a good post-harvest option for hay and silage paddocks as it replaces some of the potassium removed in the harvest.”

Supplying potassium at the post-harvest point improves the quality of the recovering pasture. “Compared to grasses, clovers are poor at scavenging nutrients from the soil and are easily out-competed if any nutrient is in short supply. In a post-harvest situation, potassium can easily limit clover growth, which has consequences for your pasture quality and nitrogen needs down the line,” says Josh.

After the final harvest it is important to replace the nutrients used by your hay/silage crop(s). Every tonne (t) of dry matter removes around 5 kilograms (kg) of phosphate, 3 kg of sulphur, 2 kg of magnesium and a massive 15 or 20 kg of potassium for hay and silage, respectively.

If hay or silage is fed out on the paddock from which it was cut, some of the nutrient content will be returned to the soil in dung or urine. However, if it is fed out elsewhere on the farm, its nutrient value goes with it. Either way, if the nutrients are not replaced, pasture quality will eventually suffer.

Replacing potassium after the final harvest is advisable. Split the applications if winter leaching is a risk, or if large amounts of potassium are required to achieve the desired soil test range. Growing plants will take up excess potassium without converting it into extra growth. This luxury consumption can elevate potassium levels in your conserved feed and/or re-growing pasture, which may contribute to metabolic issues in stock if not taken into account.

“Post-harvest fertiliser does not replace normal maintenance fertiliser. It is an extra application that takes care of the nutrients removed by the harvest alone. You can either apply replacement fertiliser separately after harvest or combine it with maintenance fertiliser, ensuring a heavier rate goes on your hay and silage paddocks,” concludes Josh.

1 DairyNZ Farm Fact 7-16 ‘Nitrogen use going into summer’, DairyNZ 2012

For more advice, talk to your Ballance Nutrient Specialist or your local Fonterra Farm Source team.

Article supplied by Ballance Agri-Nutrients