Dairy notes March 2008

With the price of fertiliser having almost doubled from last year you may well be wondering how you can keep costs/usage down.  Can you use more straight nitrogen?  Can you cut the amount of fertiliser applied?  

Soil analysis results will help identify fields where straight nitrogen can be used along with slurry.  On fields with high phosphate (P) and potash (K) indices of 2 or higher an application of over 17m³ / hectare of cattle slurry will meet the P and K requirements for first cut of silage – straight nitrogen can be used to provide the rest of the nitrogen requirements.

If the P index is 1 or lower slurry will not provide all the P required, so a compound fertiliser should be used (for example 27.6.6 or 25.5.5).  Where P index is satisfactory at 2 or above but the K index is low (0 or 1) a zero P compound such as 27.0.6 should be used along with slurry.  

An allowance can be made for the significant contribution to nitrogen supply from February/March applied slurry.  34m³ / hectare a of cattle slurry will provide approximately 35 KG of nitrogen/ hectare – a saving of about 2½  bags of high nitrogen fertiliser/ hectare or 1 bag/ acre .

A significant amount of slurry was applied during a dry mild spell in mid-December.  Little allowance should be made for the nitrogen contribution from this slurry, but the P&K will still be available.

With the possible exception of reseeds, there is no yield benefit in applying a total of more than 120 KGs nitrogen/ hectare (96 units/ acre) for silage production.  Allowing for the nitrogen in 34m³/hectare of slurry, this would mean applying 85 KGs nitrogen/ hectare – the equivalent of  6 – 6.5 bags of high nitrogen fertiliser/hectare.  If silage ground is grazed before closing off for silage, make allowance for the carry over of 50 percent of the nitrogen from the urea applied in February to the silage crop.

The current high price of cereals makes it more economic to combine winter wheat for cereals to feed as a concentrate rather than to put the crop in the silo.  Growers in suitable areas could consider renting extra land now to grow forage maize and leaving their wheat crop for grain production.  

For producers currently over the 170 KGs of organic nitrogen per hectare limit under the Nitrates Action Plan, taking the extra ground for maize could save having to proceed with the derogation application. Given the higher yield potential of maize compared to wheat, the ensiled crop can be produced as competitively as whole-crop wheat despite the higher growing costs per hectare.  

In 2007 there was a problem with poor fertilisation in a number of later sown maize crops.  It is believed that a period of wet, windy weather at pollination time was responsible, washing the pollen off the silks.  To reduce the risk of this occurring you could consider planting two varieties in the field in alternate double rows.  In poor weather conditions one variety could compensate for the other, as pollen would be produced over a longer period.  

The two varieties need to be chosen carefully – varieties which mature within 10 days of each other would be ideal.  Dr Trevor Gilliland from AFBI, Crossnacreevy suggests that under plastic, Justina and PR39G12 are a compatible high yielding, late maturing pair for use on the best sites.  Goldcob and Nescio are an earlier maturing pairing suited to marginal areas.   For growing in the open in early growing areas Crescendo and Ruler could be used.