The Value of Silage Effluent

To most farmers silage effluent is a necessary evil – and evil smelling evil at that. It’s an unwelcome by product of the silage making process that can land you in a heap of trouble with your partner, your neighbours and the law in short order. It’s a real problem to store and it’s a problem to get rid of.

So is there any “value” in silage effluent?

To see the value we need to understand what’s in it and that comes from how it’s made. Silage effluent is a combination of pure grass juices and the products of microbial actions in the fermentation process And particularly the acids produced by the bacterial fermentation. This makes silage effluent extremely corrosive as the pH is (hopefully) very low, and a very dangerous pollutant if it escapes into the aquatic environment. The low pH is obvious…

But why is silage effluent so dangerous in a watercourse?

The majority of the precious energy you have grown and harvested this forage for is, unfortunately, water soluble. This means the sugars contained in the crop can escape out into the effluent. These sugars are a great food source for a huge number of life forms, your livestock and the bugs in the AD tank, but also lots of aerobic bacteria found in the environment. In water with an unhealthy dose of silage effluent, these bacteria thrive and burn up all the dissolved oxygen in the water. This high BOD or Biological Oxygen Demand leaves none available for the vertebrates so causing fish and other aquatic life to die.  The only common farm material that can out do silage effluent in this manner (BOD) is milk.

As effluent contains a good level of the products we are trying to store – the sugars, now we can begin to see that it has some value. But it’s a tricky product to handle, it is corrosive as hell, it’s not stable when exposed to oxygen for any amount of time so….

How can you utilize silage effluent?

In the 70’s and 80’s some farmers fed relatively large volumes of fresh effluent to cattle. Trials in Canada using vertical tower silos made collecting and storing the effluent easy and the trial result were positive. Restricting livestock intakes proved difficult and there have been reports of tainted milk from cows taking a long drink at the effluent trough. In the UK clamp silos make collecting the effluent and keeping it fresh more challenging, so feeding to livestock is unpopular today.

Feeding effluent into an AD plant makes more sense but again there are issues regarding the freshness. If you feed the effluent as it is produced, you run the risk of unbalancing the ration with the resultant double dip in gas production as the bacteria adjust to both the start and the stop of the effluent content of the raion.

These issues led most farmers to abandon utilizing effluent as a feed and to exploit it as a fertilizer instead. There are considerable benefits to using effluent in this way, particularly in dry weather periods as it can give the crop a good liquid fertilizer. Due to the concentrated nature of the effluent, it is advisable to dilute if 1:1 with water to avoid scorching leaves. Don’t be tempted to use slurry as the diluent as it will still be too concentrated and, more importantly, mixed silage effluent and slurry can produce highly dangerous hydrogen sulphide gas that can be fatal.

Obviously you need to take great care not to get run off during spreading. You also need to be alert to the risks of spreading in very dry weather when effluent can run down though cracks in clay solid and on into the water courses.

So do we need to give up on the idea of feeding effluent?

No, there are loads of options that can utilize the feed value without the troublesome storage issues. What you need is a method of absorbing the effluent in the clamp and stopping it escaping in the first place. The most obvious solution is to leave it in the field before the chopper even goes near it – in other words, increase the dry matter at harvest. This is the most effective measure and the cheapest, but there are other things you can do.

The first attempts to absorb effluent involved placing a layer of small straw bales on the bottom of the clamp. Although this works to a limited extent, it’s just not practicable in today’s harvest systems. Chopped straw layers within the clamp offer a much better solution, speeding up clamping and ensuring a consistent feed ration across the whole depth of the clamp.

Recently pellets have become a more popular solution, made from a variety of materials such as straws and chaffs to sugar beet pulp and feed concentrates. These are more easily dosed into the clamp and can incorporate some of the concentrate element of a livestock ration at ensiling. This obviously has benefits as the silo can then contain a more complete ration. A word of caution however, using expensive materials as the absorbent product comes with its own risks as a poor fermentation risks losing both the forage and the concentrate so think very carefully about this option.

 If you want to discuss how to utilize the value of your silage effluent or any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com