Fertilising second-cut grass silage
Specialist on the Teagasc Signpost Programme, Mark Plunkett shares key fertiliser advice for farmers planning a second cut of silage.
Second-cut silage will be a valuable crop on many farms to replenish and build silage reserves for the coming winter. This crop tends to be lower yielding compared to first cut silage.
Where first cut has been cut, it is important to ensure that second-cut crops are fertilised adequately to ensure a good yield of grass at harvest time.
The value of cattle slurry
Where cattle slurry is available, it will be a valuable source of phosphorus (P) and potassium (K) especially to replenish soil reserves and possibly supply P and K depending on soil fertility levels. Aim to apply cattle slurry after first-cut silage and empty slurry tanks before the winter period.
Where a second cut of silage is planned, consult with table 1 below to see what level of nitrogen (N) cattle slurry can supply depending on application techniques. Low emission slurry spreading (LESS) increases the recovery of N by 3 units / 1,000 gals and reduces N losses as ammonia. LESS delivers slurry nutrients more precisely across the spread width giving a more targeted nutrient placement.
Table 1: Available N, P and K values for cattle and pig slurry (units/1,000 gals)
| Manure type | Application method | N | P | K |
|---|---|---|---|---|
| Cattle slurry (6% DM) | Low emission | 6 | 5 | 32 |
| Pig slurry (4% DM) | Low emission | 19 | 7 | 20 |
What fertiliser to apply?
Fertilise second-cut grass silage based on crop yield potential. Table 2 below shows the fertiliser requirements based on a grass dry matter yield of 2 to 4t DM /ha (4 to 8t fresh grass/ac). Suggested fertiliser programmes are shown with and without cattle slurry at various rates depending on grass yield. Don’t forget sulphur as it has a key role in increasing grass dry matter (DM) yield, fertiliser N efficiency and reducing N leaching. For second-cut grass silage crops, apply 8-15kg S/ha (6-12 units/ac) per cut.
Table 2: Second-cut silage N, P and K and S requirements (off-takes)2,3,4,5,6 based on grass yield (DM) and fertiliser programme
|
Grass yield (ton DM/ha)3,4 |
N kg/ha (units/ac) |
P kg/ha (units/ac) |
K kg/ha (units/ac) |
S kg/ha (units/ac) |
Fertiliser options1 | |
|---|---|---|---|---|---|---|
|
|
|
|
|
|
No slurry1 |
Cattle slurry gal/ac2,6 |
|
2 (4t/ac fresh grass)5,6 |
50 (40) |
8 (6) |
50 (40) |
8 (6) |
2 bags/ac 15-3-20+S 0.2 bag/ac ProUrea |
1,500gals/ac 0.8bags/ac ProUrea + S |
|
3 (6t/ac fresh grass)5,6 |
75 (60) |
12 (10) |
75 (60) |
12 (10) |
3 bags/ac 15-3-20+S 0.3 bag/ac ProUrea |
2,000gals/ac 1.25 bags/ac ProUrea + S |
|
4 (8t/ac fresh grass)5,6 |
100 (80) |
16 (13) |
100 (80) |
15 (12) |
4 bags/ac 15-30-20+S 0.4 bag/ac ProUrea |
2,500gals/ac 1.7 bags/ac ProUrea + S |
1Protected Urea (46%), 2Protected + S (Urea 38% + 7.5% + NBPT). 3Apply 4kg P & 25kg K per tonne of grass dry matter
(DM). 4N, P & K advice for crop off takes based on grass DM yield at harvest time. 5Apply additional P & K for soil
fertility build up after grass harvest refer to Teagasc Green Book for specific rates. 6Fresh grass @ 20% DM. 6Slurry
applied with low emission applicator (6-5-32).
The above was first published as part of the Future Beef eNewsletter for May. For more tips and advice from the Future Beef Programme, visit here.
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