Delivering enough nutrients to silage ground

Published 11 April 14

In the next week or two many dairy farms with sheep will be closing out fields for a silage cut in late May or early June, says Chris Duller, independent grassland and soils consultant.  If you want to maximise quality and yield it is vital that the crop receives enough nutrients.

The table below indicates the levels of phosphate (P) and potash (K) needed at different soil indexes. Where potash indexes are low (0 and 1) the application needs to be split between spring and autumn.

If a field has been mucked since last year then you need to take account of that P and K which is still going to feed this year’s crop. Spreading 2,000 gallons/acre (22.5m³/ha) of slurry (4% dry matter) will have given around 8 units P, and 46 units K - 5t of FYM/acre will have given 20 units P and 72 K.

Not supplying adequate P and K will mean the crop won’t respond as well to nitrogen so won’t produce the leaf area or the levels of protein and sugars required to make high quality silage. Oversupplying nutrients will mean higher nutrient losses, both a financial and environmental concern, and can also negatively affect crop quality.

  P&k big

Nitrogen applications need to be driven by the level of intensity of your system and youryield and quality targets. The old adage of 2 units/day isn’t far away from what a crop requires – meaning around 80-100 units/acre for a 6-7 week shut. Certainly aim for the higher end with Italians or new leys, where response will be high. 

If you applied nitrogen in March for early grazing you will get a carry-over of about half of that nitrogen. Take account of that and also the nitrogen from muck, about 15 units N from 2,000 gallons (22.5m³/ha) of spring applied slurry and 9 units from 5t/acre (6.25t/ha) of FYM.