Silage quality is made up of not just the nutritional quality of the crop when it is cut, but also the fermentation and hygienic quality. Managing air is a critical step in reducing damage and losses in silage caused by these ‘bad bugs’ or spoilage organisms that thrive on air.
Getting rid of the air
The bacteria that efficiently ferment fresh forage into silage grow in the absence of air. Those that need air to grow are spoilage organisms which we don’t want. It is therefore important to exclude air from the stack or pit through good compaction. The crop dry matter should be high enough to avoid silage liquor leaching out but not so dry that it is hard to compact. For drier crops, a shorter chop length can help with compaction. The crop should be spread in thin layers as the stack is built or the pit filled, and each layer compacted well with a suitable heavy vehicle.
Keeping the air out
Once the stack or pit is finished it needs to be sealed well to keep the air out and starve spoilage organisms of oxygen. The sooner this is done the better. If a conventional plastic cover is used (eg black and white cover), this should be well sealed along the edges and covered all over with touching tyres to hold the cover down against the silage. Some air will still pass through a conventional cover, often resulting in a layer of top spoilage.
Alternatively, an oxygen barrier sheet, e.g. Silostop®, which has been tested and proven can be used to greatly reduce the movement of air into the silage. One layer of SiloStop® is the equivalent to 60 black and white covers based on the amount of oxygen it lets through. Oxygen barrier sheets need to be covered by either a conventional black and white cover or a green UV cover to protect them from UV light and damage caused by birds and rodents. They need to be very well sealed around the edges but don’t require touching tyres.
Managing the silage face at feed out
The stack face should be kept tight and tidy, with minimum loose spilt material at the base, so spoilage organisms can’t grow, wasting energy and producing heat. Any visible spoilage on the top or sides should be cut out and put in a compost heap.
Watch for heating
Thermal camera images often show significant heating in the surface layers of silage stacks and especially in loose material at the front. Heating is energy lost and is a clear sign of significant spoilage. A five degree increase in silage temperature (compared to the base of the stack) can result in 1.2% dry matter loss per day1. If the top meter of a 15m x 50m stack2 is exposed to too much air and is heating >5 ̊C more than the base of the stack this could equate to over $400 worth of silage lost per day. Significant nutrient value is lost if silage is heating above 35 ̊C.
Get in contact with the team at Nutritech who have tools and resources to help minimise air and losses from heating in your silage.
1. Lallemand LalSil Technical Survey Guide
2. 750m2 assuming a density of 180kgDM/m3 and silage is valued at 25c/kgDM
This article was originally published in the Green to Gold feature of the NZ Rural Contractor & Large Scale Farmer magazine in September 2020.