Managing spring fertiliser and slurry applications in a wet spring

Nitrogen and sulphur levels will likely be lower than expected this spring

Nitrogen and sulphur levels should be the first consideration when planning spring fertiliser.

Typically 70 - 80% of all root mass in a grass sward is in the top 7.5cm. In reasonable winters you would expect that some nitrate and sulphate would remain in this surface root zone, but with over a third more rain having fallen during autumn and winter it’s reasonable to expect that very little nitrate and sulphate remains.

On intensive grazing farms, apply up to 25-30 kg/ha (20-25 units/acre) of nitrogen as a 1st application. Any more than this is a waste, as daily grass growth rates in early spring will still very low (<5 kg/ha DM).

Nitrogen should always be applied together with sulphur, particularly in early spring when sulphur levels will be low following winter leaching and reduced mineralisation in cold soils.  YaraBela Axan (27% N+3.6% S) or YaraBela Nutri-Booster (25% N + 2% S and Se) are both compound nitrogen plus sulphur fertilisers which spread evenly and have the correct nitrogen to sulphur ratio for grass. Keep an eye on soil temperature’s and if soil temperatures are at 5°C or above and soil conditions are dry enough, not frozen and heavy rain is not forecasted then it’s safe to spread.

Paddocks with low soil K indices will benefit most from slurry applications

Scope to apply slurry rather than fertiliser nitrogen on paddocks with the lowest grass covers. Avoid slurry on heavier covers until after 1st grazing. Remember that ammonia (nitrogen) losses from slurry double for every 5°C rise in air temperature, so spring applications are encouraged. The waterier the slurry the lower the ammonia loss, as this type of slurry infiltrates the soil more quickly trapping the ammonia in the soil.

Prioritise slurry for low potassium soil index grazing paddocks (especially ones which had bales removed last year) and silage fields. Reduce the fertiliser nitrogen application rates on paddocks that have received slurry. Allow for 6 units/N per 1,000 gallons with splash plate and 9 units/N with trailing shoe. Leave 5-7 days between fertiliser and slurry applications or vice versa.

Keep an eye on slurry application rates, as heavier application rates on fields closer to the yard will play havoc with the farms fertility balance. For instance, if the target application rate is supposed to be 1,500 gallons/acre and in paddocks closer to the yard it’s 2,000 and further from the yard it’s 1,000, this means that the extra 500 gallons that the paddocks closer to the yard receive is equal to the annual potassium maintenance requirements for grazing. So, if you’re trying to build potassium fertility on certain paddocks you might wonder why they’re not rising.

Target low soil P paddocks with compound NPKS fertiliser

Target paddocks with a phosphorus (P) index of 1 or 2, with a compound fertiliser, such as YaraMila Super Booster (25-2.2-4.2+2% SO₃+Se) as soon as conditions allow, to kick-start and maintain grass growth this spring.

Remember, cold and wetter spring conditions exacerbate the effect that low soil P has on phosphorus availability and grass growth, with phosphate availability significantly reduced in saturated fields. These conditions increase the solubility of soil iron and aluminium which in turn affect the availability of soil phosphate. Generally, even in drier years there is more than a 20% growth response from combining sulphur, phosphate and nitrogen in early spring applications, so be sure to use a compound NPKS fertiliser to get your grass off to the best possible start

Find more information on grassland nutrition