Neil Griffiths
Technical Specialist Pasture Production
NSW DPI
Making spring silage will depend on seasonal conditions that enable a genuine surplus of forage to grow or a major problem in cropping areas such as drought, late frost or hail where silage may be a salvage exercise. Choice of silage method will depend on machinery and contractors available and relative cost. While bulk chopped silage may be a cheap option, wrapped bales will always incur the cost of plastic and therefore must be of premium feed quality to be profitable.
Early thinking about spring silage should include maintenance of machinery, storage areas and tracks, sourcing plastic, twine or net wrap and inoculants. Growers making early and regular contact with contractors or vice-versa will help reduce problems when everyone is busy.
Choice of which paddocks to cut will consider the obvious topography, access and feedout issues with some people preferring to cut convenient paddocks while others will graze close paddocks and cut further away to reduce stock walking.
Soil fertility and weed management are major considerations when we start getting into detail on paddock selection and management.
Silage removes large amounts of nutrients including nitrogen (N), phosphorous (P), potassium (K) and sulphur (S) which must be allowed for and monitored using soil tests. It can be a great way to reduce nutrient build up in effluent disposal areas provided withholding periods are observed to minimise animal health risks. In preparing for spring silage nitrogen and potassium will be need to be managed to ensure good growth and yield as well as feed quality and high quality silage. Deficiencies will limit yield but excess can also be a problem.
If potassium is needed, and it often is if silage or hay is regularly taken from a paddock, then split applications early in spring to allow growth and again after silage harvest to replace nutrients will reduce the risk of luxury uptake. This is where the plant absorbs more K than it needs meaning you lose fertiliser while the silage has excess K with possible associated feed quality issues.
Nitrogen also needs to be applied sensibly. Topdressing early in spring to ensure good growth is usually essential but excess nitrogen can interfere with silage fermentation and nitrate poisoning is a risk. Both are unusual in Australian silage but should be considered.
Topdressing rates for ryegrass will depend on if you take a grazing management priority and harvest at three leaves or want to optimise your yield of high quality silage and harvest at the boot or early head emergence stage of growth. One guide to how much fertiliser should be applied after the grazing prior to silage harvest is to allow for the nutrients removed in the silage which would be 30kgN/tDM if the silage was 19% crude protein with about 25kgK/tDM. We often under estimate how much N and K is removed in silage and hay.
Weed management is also a major consideration in paddock selection both from a silage quality and weed control perspective. Using silage for weed control is highly effective and becoming more important as increasing herbicide resistance issues affect more farmers. Silage will help reduce weeds in two ways. Early harvest compared to hay means that often the weed seed is not fully developed and also the silage fermentation process will significantly reduce weed seed viability if there is any mature seed harvested.
From a silage quality perspective grass weeds may not be a big issue but broadleaf weeds can affect silage quality. Many broad leaf weeds such as Capeweed have a high buffering capacity and low WSC levels making it hard to get a good fermentation. Weeds such as Fireweed and Patersons Curse also contain pyrrolizidine alkaloids which cause liver damage. While silage fermentation may reduce the risk of nitrate or prussic acid poisoning it does not reduce the risk from these alkaloids. When choosing which paddocks to cut for silage either control weeds early or avoid very bad weed infestations or if the paddock is patchy then it can be baled to clean up the paddock and discard bales from the worst weed patches.
Note that these comments on weeds and poisoning apply to bulk silage. Drier baled silage or haylage has less fermentation and hence less affect on weeds.
Another question which sometimes influences paddock selection is disease or insect damage. This especially applies to rust where the general advice is to make a decision early and avoid badly infested crops because the rust on leaves is dead material which could have a negative affect on fermentation and feed quality similar to any dead matter that is mixed in with silage. Having said that the winner of the 2010 NSW Hay and Silage Feed Quality Awards was a silage made from a stripe rust infested wheat crop from Forbes where the decision was made early and the crop cut for silage in the boot stage, testing 11.0 MJME/kgDM and 19.0 % crude protein.
Finally when paddocks for silage are identified make sure you remove hazards such as irrigation pipes, electric fence posts and pasture harrows and mark rocks or stumps early while you can see them.