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Nitrogen – your autumn advantage

Pasture-enhancing nitrogen can help you manage autumn’s juggling act.

In autumn, dairy farmers need to balance the desire to get just a bit more milk in the vat with the need to get more fat on the back. Good body condition scores going into winter are essential to set stock up well for mating, pregnancy and the following season. Drying off too late can make it hard to achieve target body condition scores and at the end of summer, your pasture may not be in the best shape, which adds to the challenge.

In late summer through early autumn, pasture can be very high in fibre and lacking in protein and essential nutrients. Drought exacerbates this issue and a short growing season can also affect the quality of hay or silage you may be using. It is hard for rumen microbes to break down fibre – essentially it is wasted energy at a time when you need to build stock condition or are trying to extend your milking.

The positive news is that autumn can be a great time to grow grass. Rainfall can still be a bit fickle, but soil temperatures are generally good – often warmer than early spring. Using nitrogen to boost grass growth can be an effective way to get the quality feed you need at this critical time.

Research indicates that you can apply nitrogen straight after the first drought-breaking rain.i This contrasts to the traditional advice, which was to wait until later, as the first rain is sometimes followed by a further dry period. Trials on drought-affected land in Hawke’s Bay and the Bay of Plenty showed that applying moderate rates of nitrogen fertiliser (25 or 50 kg N/ha) after the first rainfall produced useful pasture responses only a few weeks after application. First harvests yielded between four and 10 kilos of dry matter per kilo of N applied. Plus the effect of the applied N was not lost if another dry spell followed. The response carried on when more rain arrived.

The overall yield over consecutive cuts in the trial was 12 kg of dry matter per kilo of N applied. Whether you’re extending milking, improving condition scores or both, this extra quality feed would help considerably.

Product choice critical

Do not be tempted to interpret the post-drought response research results as a license to apply nitrogen in dry conditions. That all-important five to 10 millimeters of rain or irrigation is definitely required within eight to 10 hours of application to reduce nitrogen loss from ammonia volatilization. Getting the nitrogen into the soil is vital.

SustaiN and PhaSedN are great choices for autumn. Both have the advantage of Agrotain® nitrogen stabliser, a product that blocks the action of urease enzymes in the soil. This reduces the rate at which the urea converts to ammonium, which in turn reduces volatilisation. This gives you more flexibility in terms of the timing of application.

PhaSedN has the additional benefit of elemental sulphur. PhaSedN is a perfect autumn nitrogen option for dairy farms that don’t require phosphate but need to boost or maintain sulphur availability to maximise production. The sulphur in PhaSedN is in the elemental form rather than soluble sulphate. This means that if it is applied in autumn, it will remain in the soil over winter and slowly release to improve supply in spring when pasture starts growing again. It is a great way to make the most of autumn and set the farm up for spring.

Josh Verhoek
Science Extension Officer
Ballance Agri-Nutrients

“The effects on soil, herbage and dry matter responses to applied nitrogen after prolonged low soil moisture conditions,” Research report for Ballance Agri-Nutrients, 2008