Making silage in a cold dry spring
If you farm in the UK you are generally in a fortunate position! Forget for just a moment the issues of Brexit, Covid-19, TB and fly tipping, compared with many of the worlds farmers, UK and Western European growers enjoy a relatively warm and wet climate to assist with the day job. The spring of 2021 might have just given us a taste of what much of the world has to face, cold dry conditions. For anyone trying to produce forage crops it’s a challenge we are not that familiar with.
Coping with the cold
The problem for crop growth in the cold is very similar to drought stress. Get both together and the plants really suffer. The additional problem many growers face is that we didn’t expect these conditions and so applied fertilizers expecting a “normal” spring. This fertilizer, in particular the nitrogen element, has not been taken up by the plants during the cold, droughty conditions. As soon as we get some rainfall – such as that over much of the UK in early May, and the temperatures begin to rise, then the plants hit the “all you can eat buffet”.
Problems in silage with high nitrate levels
This nitrogen uptake will eventually be turned into proteins but in the interim it is still soluble within the crop. High nitrate levels – above 1000 parts per million, or 0.1% - in grass fed to animals will reduce intakes, reduced milk yields with weight loss and diarrhoea. In silage high nitrate levels can cause all of the above whilst also producing very poor fermentations. This type of silage that’s low in sugar will take a long time to get to a stable pH. During this time proteins will be converted to ammonia by bacterial actions and nitric acid can also be produced. The resultant silage will not only be mildly toxic to the livestock, but it will also have lost much of its feed value. At very high nitrate levels (6000 parts per million) this silage can even be fatal to humans if toxic nitrogen dioxide gas is allowed to form.
How do you know when silage is safe to cut?
The time taken to convert the nitrates in proteins will depend on temperature, light levels, growth stage and variety so it’s hard to predict. In a “standard” growing season it’s possible to predict with some safety margin but in the conditions that much of the UK has experienced in 2021, it’s almost impossible. It is also far too risky to just guess and hope for the best. The only solution is to test and, luckily, it is easy, quick and cheap, and something you can do in the field by using a strip test kit.
Making silage from low sugar crops
If nitrate levels are safe, below 1000 ppm, then it’s possible to make good silage with low sugar content forage. At sugar levels below 12% dry matter the bacteria are going to struggle to find enough sugar to make lactic acid fast enough and get the pH stable in a short time. This sort of silage is going to need some help to prevent excessive losses – and you have a couple of options. Today most farmers will look to a silage additive to help with “difficult” silage crops and that might be the best solution. Not all additives are the same or even work in the same matter. Many are bacterial inoculants that give the silage a huge hit of friendly bacteria that will generally be sufficient to ensure a good fermentation. The thinking is that little or no sugar will be wasted by unhelpful bacteria if the dining room is full of good guys making lactic acid. However in this case making sure it’s mostly good guys at the table is only part of the issue, the main problem is that the table doesn’t have much on it!
Stepping back to the 60’s
In the old days, one of the jobs for the boys was to walk over the silage clamp with a watering can full of brown sticky stuff as each layer of grass was spread. The adding of molasses was to give a sugar boost to the bacteria in the form of an energy drink. In low sugar forage this is still the best solution for bacteria that need to be “given some wings”. An alternative is to use an additive that contains enzymes that break down cellulose and convert it into available sugars. The down side here is that the forage is already below par and you are really just using feed value to get a good fermentation. Molasses might be a messy product to add but at least you are adding to the silage and not taking away!
Dry matter matters
The dry matter of your silage is always important – it’s especially so with low sugar crops. Increasing the dry matter by wilting a bit longer will concentrate the sugars and the resultant silage will require less lactic acid to reach a stable pH. The temptation may be to ensile a more bulky crop with lower dry matter as the pile looks a bit bigger, but all you have done is bring home water that dilutes the acid the bacteria are busy producing. In all other respects, making silage in cold, dry conditions is just a case of doing things right. Don’t be tempted to cut too low as you risk increasing contamination and reducing re-growth – just continue following good practice. The first cut is only the start of the season!
If you want to discuss any of the aspects of silage making covered in this series – contact Jeremy Nash at Jeremy@silageconsultant.co.uk
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