Fertiliser use after first cut

Published 24 May 13

Fertiliser after first cut

Elaine Jewkes, grassland specialist at GrowHow, talks about fertiliser usage after first cut

It's worth spending a little time considering nutrient inputs for after first cut, so that the grass has the best chance to get moving again and produce quality forage, whether for grazing or a further cut.

If the field is going on for a second cut, it is a good time to make use of slurry. Be sure to account for the nutrients it supplies - both for cost effectiveness and also to avoid building P and K indices to high levels. In most cases, a modest dressing of slurry will provide all of the required phosphate and much of the potash for second cut, meaning that an NKS fertiliser will be ideal to supply the remainder of the nutrient requirement.

While it seems very unlikely that there won't be sufficient rain between now and second cut to wash slurry spread by splashplate from the grass leaves, the best option is to use a low-trajectory spreader such as a trailing shoe or an injector. This will ensure that as much as possible of the available nitrogen will be used by the plant rather than being lost to the atmosphere. These techniques also minimise sward contamination.

If slurry is not used or the soil indices are low, an NPKS fertiliser should be used. If sufficient slurry is applied such that no fertiliser phosphorus or potash is needed, use an NS product to ensure the grass gets the necessary sulphur boost. Late spring onwards is when the best response to sulphur is usually seen, so do make sure the grass has everything it needs for yield and quality. Because deposition of sulphur from the atmosphere is now so small, the recommended rate for sulphur is 40kg SO3/ha per cut.

Apply fertiliser within a week of cutting to get the best yield response. Nitrogen rates for second cut should normally be around 90-100kg N/ha, including the available N in any slurry applied. A note of caution is needed - it's best not to apply slurry and fertiliser too rapidly one after the other, as the combination of moisture, carbon and nutrient source can provide excellent conditions for denitrification. Leave a gap of a few days between the two, so that any temporary surface waterlogging from the slurry can dissipate. 

Where grass is going back into grazing, potash is needed, unless the soil indices are three or above, as cutting will deplete levels. Up to 30kg/ha of potash should be applied for one or two grazings. This can be supplied by an NKS compound, with the advantage that some all-important sulphur will be supplied as well. If insufficient phosphorus was applied for first cut, using an NPKS compound instead will ensure that the grass is not deficient. This should ensure quality grazing going through the summer.