Getting Silage Dry Matter Right

If you have been reading any of the other blogs in this series, you will have been constantly hearing about how important the dry matter, or DM, of silage is. In this issue I will attempt to explain why it’s important, how to measure silage DM and what the consequences of not hitting your target dry matter levels can mean.

So what is silage dry matter?

 In essence, it’s the bit of the crop that isn’t water. Just like humans, most crops are more water than anything else and forage crops are no different. The dry matter percentage of the crop changes as it grows and matures. For maize and wholecrop cereals it’s really easy to see the crop turning from lush green to golden brown as the water percentage drops. For grass it’s not so visible but the dry matter increases as the plant matures and the stem becomes more “woody”. The rise in dry matter will depend on the weather, the crop nutrition and the species (diploid crops having higher DM than tetraploids). At maturity silage crops will be between 15% and 40% dry matter. Grass will be in the 15% to 20% range and whole crops and maize being 25% to 40%. This means that the bit of the crop you want, the energy, the proteins and the fibre are the dry matter part of the crop; the rest is just water.

 If you just think about that for a moment, a lovely 16t trailer load of grass silage heading into the clamp has over 13t of water on board and less than 3t of actual dry matter! Or to put it another way, for every ten trailer loads at the clamp, eight of them are just water and only two have any silage in them! – or do they?

 Perhaps that’s a bit simplistic, in truth most of the “feed” elements in the crop are water-soluble - even hay only reaches around 85% dry matter. And therein lies the problem, if the silage is really wet, a lot of these valuable feed products will escape with the effluent and seep away. On the other hand, were you to produce a product at 100% dry matter it would be pretty unpalatable to livestock and AD bugs alike – just imagine instant coffee without water…

So the water element is important, but we want silage that’s not too wet and not too dry.

 How do I get silage DM just right?

 Cutting at the right time is vital – as the old adage should go “make silage while the sun is shining”. You can’t control the dry matter levels in the crop, but you can control the dry matter level of the silage coming in to the clamp by choosing the cutting day. Obviously in the real world we all get caught out by the weather occasionally, but the aim should be to control the DM levels at harvest as far as possible by harvesting in good weather. Dry weather will mean you don’t bring in any additional water and will give you a better chance to increase DM by wilting the mown silage.

So for grass silage you should be aiming for 20% to 28% dry matter for the incoming crop and for maize and you want 28% to 35% dry matter. Whole crop silage will be higher still with dry matter at about 40%.

How do I test silage Dry Matter %?

You may be skilled in wringing crops by hand and judging the juices as they squeeze through your fingers. This is how I was first taught to measure silage dry matter, but this was before the days of a microwave oven. The best solution is to make use of the kitchen equipment (maybe whilst no one is looking!) or perhaps you have a suitably set up farm office. Take some fresh crop sample and weigh out exactly 100g into a plastic or glass container. Microwave it for 3 minutes; take it out and weigh again. Record the weight and give it another 1-minute blast in the microwave then weigh again. Keep doing this until the weight doesn’t change anymore. You will now just be left with dry matter as you have boiled off all the water in the microwave. If you started with exactly 100g, the weight you are now reading will also be the dry matter percentage without any additional mathematics.

So what happens if the dry matter is too low?

If your silage dry matter is too low, you will be causing all sorts of issues. Firstly your guys have been harvesting and hauling tonnes of unnecessary water wasting time and diesel. But that’s only the small matter; the big losses will be the energy and proteins lost in the clamp. The sugars will be leaking out in effluent and the proteins will be broken down by prolonged fermentation and excessively low pH in the silage. Extremely low pH form wet silage will also increase acid attack on the walls, floor, effluent channels and apron of your clamp. So not only are you losing feed value, you are destroying your building assets as well. Silage of too low dry matter percentage will be costing you a lot of money.

So what happens if the dry matter is too high?

Having silage with a really high dry matter can lead to greater in-field losses. Leaves are the most vulnerable bit of dry maize and grass crops as headers and rakes can easily cause leaf shatter losing this part of the crop entirely. Losses in the blow can also be quite significant, especially in windy weather when a dry crop struggles to all make it from the spout to the trailer. Back at the clamp, silage that too dry is difficult to compact, leading to a poor consolidation and poor fermentation. This also gives increased risk of unwanted blooms of yeasts and moulds along with surface and edge losses.

So just like Goldilocks’ porridge, it is really important that the DM of your silage is “just right”. If you want to discuss how to target and achieve the ideal silage DM percentage or to discuss any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com