Fertilising second-cut silage: What’s needed?

Many farmers took advantage of the good spell of weather over recent weeks to save first-cut silage.

However, as feed reserves are tight on many farms after a difficult spring, the attention must now turn to growing the best crop of second-cut silage possible.

When it comes to supplying adequate nutrients for second cut, farmers should aim to make the best use of slurry; application rates of 2,500-3,000 gallons per acre are advised.

1,000 gallons of cattle slurry (7% dry matter) typically contain: 18 units of nitrogen (N) – 6-7 units of which are available to the grass plant; 5 units of phosphorous (P); and 30 units of K.

Pig slurry may also have a role to play at farm level and, if obtainable, it could be used to provide valuable nutrients to a grass crop. Teagasc work suggests that 1,000 gallons of pig slurry (4% dry matter) should contain 21 units of N, 7 units of P and 20 units of K.

Where slurry is used to bolster nutrients, a time lag of five-to-seven days should be applied between slurry and artificial fertiliser applications to reduce the risk of nutrient losses.

If slurry has been applied, farmers must then work up to 70 un/ac of N on old permanent pasture or 80 un/ac on recently reseeded ground or swards containing a high proportion of perennial ryegrass.

fertiliser
Image source: Shane Casey

Teagasc offers the following recommendations for P and K allowances for second-cut silage:
  • Index 1 soils: 24 un/ac (30kg/ha) of P and 56 un/ac (70kg/ha) of K;
  • Index 2 soils: 16 un/ac (20kg/ha) of P and 40 un/ac (50kg/ha) of K;
  • Index 3 soils: 8 un/ac (10kg/ha) of P and 28 un/ac (35kg/ha) of K;
  • Index 4 soils: 0 un/ac (0kg/ha) of P and 0 un/ac (0kg/ha) of K.

In addition, grass silage crops have a requirement of 20kg/ha of sulphur (S). The application of S to soils where it is required will improve grass dry matter yields and quality; it helps to maintain an optimum N:S ratio and allows N to be used more efficiently.