Growing grass silage with both good quality and good yield is a key component of the overall feeding budget for the farm. Making enough silage is important so that you have sufficient feed for the winter (or summer! … given our recent weather patterns!). But having that silage of as high a quality as possible is also important to maintain good animal nutrition and performance without having to spend excessively on more expensive concentrate feeds.
Growing good silage requires having a good soil nutrient programme in place to feed the silage sward. Here, we briefly develop 2 components of this.
1) Soil pH, phosphorus and potassium levels to drive yield
Silage crops remove much more P and K from fields than grazing does. When cows graze, they leave a lot of the P and K that is in the grass behind them in the field in their dung and urine. However, silage cutting takes all of this P and K out of the field in trailers. A good first cut crop of silage will take up to 20 units/acre of phosphorus (P) and up to 100 units per acre of potassium (K) out of the soil. Over the year, this needs to be replaced or soil fertility will be pulled down and will limit the field in future years. Slurry is the best way to get these nutrients back to the field if possible. If not, PK fertiliser such as 0-7-30 or equivalent should be applied. Also, soils low in P or K should receive additional applications of fertiliser to build them up. Applying lime or soil conditioner to keep soil pH close to the target of 6.3 is also very important.
2) Nitrogen, Sulphur and Protein
Applying Nitrogen (N) for silage is essential to drive grass growth, as it is a key component of protein. However, Sulphur (S) is also a key nutrient and is important to balance the nitrogen. Every 12 units of N used by the crop will require 1 unit of S to balance it for optimum protein production in the grass. Nitrogen can also be a factor when ensiling grass where free nitrate levels in the grass remain high close to cutting. This increases free ammonia in the preserved silage and reduces protein quality and palatability. N-PROCESS and Nutri-SYSTEM fertilisers can help to reduce the impact of free nitrate and give more flexibility with cutting date, particularly in difficult harvesting conditions.
Example NPK programmes for silage
These programmes will suit a good soil fertility situation (Index 3). Low P fields should get extra 10-20 units/acre of P, in spring if possible. Low K fields should get extra 25-50 units/acre of K, in late summer / autumn if possible. If slurry or 0-7-30 is not applied before closing silage ground, it should be applied after cutting to maintain long-term soil fertility levels. Avoid applying high rates (more than 70 units/acre) of K in spring. Apply the balance after cutting.
AUTHORS: Chris Corrie and Stan Lalor; GRASSLAND AGRO