Spring Nitrogen management to promote grass growth

The same principles apply whether its grass for grazing or silage. We know that applying a N source (as slurry or fertiliser) when soil conditions and temperatures are at 5-6^oC and rising and with a favourable weather forecast will increase the supply of grass over the subsequent 6 weeks compared to holding off until later in the spring when growing conditions are more favourable.

N has the effect of stimulating growth earlier than it would otherwise be. The response to this early N will be greatest for more productive ryegrass swards. The exact timing of this initial application will vary across the UK, for the south of England and Wales it is probably early February but for Scotland it may well be a month later.

For silage, tack grazing should have finished in December, as over grazing and grazing into the new year is going to slow grass growth and is shown to reduce 1^st cut silage yields. Slurry is a valuable source of nutrients for first cut silage and often tanks have to be emptied in January, but if applications can be delayed till the soil conditions outlined in the second paragraph exist then slurry N utilisation will increase.

As a guide, if slurry is applied in January, then any nitrogen, phosphate, potash or sulphur fertiliser that is required should be applied by the end of February/early March. For later slurry applications, then the fertiliser should be applied no later than 6 weeks from the planned cutting date. These first cut silage crops need a sulphur containing fertiliser as there is not enough sulphur in slurry alone.

For grazing, we would recommend applying 80 kg/ha of Nutri Booster when the soil reaches the conditions outlined in the second paragraph and then a second application of 160 kg/ha of Nutri Booster 4-5 weeks later when growing conditions are hopefully improving. In terms of herbage growth, N response and N use efficiency, a recent study by Teagasc, Moorepark demonstrated that the most effective strategy for early spring N applications was to apply total of 60 kg/ha of N by early April, split 20/40 for the first and second application.

Finally, don’t leave it till the last minute to buy fertiliser as delivery might not be as prompt as you might like. Not having the fertiliser could cost you more if you’re later applying it. You will end up with less grass, making costly fertiliser even more expensive.