When we took silage samples on the Footprint Farms last autumn, quality was poor in some cases. All farmers had good silage, but also had some lower quality silage on their farms. In an effort to tackle this quality issue, we have decided to take sugar and nitrate tests ahead of harvesting for silage. Taking these samples a few days before you intend to cut lets you know if the crop is ready, particularly for nitrate levels.

If nitrogen is too high in the grass, then harvest may need to be delayed as this can lead to poor fermentation.

We also have to consider the weather. If silage is almost ready to cut and a bad spell of weather is on the way, then realistically, if nitrate is slightly high, the grass will be cut anyway as the delay from and the effect of the weather could have a bigger impact on silage quality. But if weather is good and the contractor is willing to wait, then it should be considered where appropriate.

Testing nitrate levels

Testing for nitrates is important, as if nitrogen levels are high in grass when it is cut and ensiled, this can lead to poor-quality fermentation and silage.

In general, the rule is that grass uses two units of nitrogen per day. Some days it will use less and some more, but it generally balances out. So, if you spread 100 units of nitrogen per acre on your silage ground, you shouldn’t cut it until at least 50 days later. In a dry or cold year, nitrogen may not be taken up by the crop for a long time and then rain might come and a flush of nitrogen is released. This also needs to be considered. Testing for nitrates lets you know if levels are low enough to cut the crop.

What you need

  • Scissors.
  • Clean basin or bucket.
  • Portable blender.
  • Nitrate test strips.
  • 100ml beaker.
  • Deionised water.

    • Procedure

  • Take a number of samples of grass from across the field in a W shape to get a representative sample.
  • Cut the grass samples at the bottom with scissors or shears to resemble what the mower would do.
  • Mix the sample and weigh out 10g of grass using weighing scales.
  • Place the grass in a portable blender along with 100ml of deionised water. Blend the sample for 20 seconds. If you don’t have a beaker or jug to measure, you could use a new syringe with no needle. Pour the mixture into the beaker and place a nitrate strip into the juice and allow it to stand for 10 seconds.
  • Compare the colour on the nitrate strip to the different colours on the nitrates test strip packet or bottle.
  • To do a second test or a test on a different field, clean the beaker with deionised water (free of nitrates) to ensure you are happy with the reading. You might have deionised water for batteries or even for putting in your clothes iron – nitrates levels should be below 1,000 parts per million.

    • Testing for sugars

    What you need

  • Scissors.
  • Clean basin or bucket.
  • Garlic crusher.
  • Refractometer.
  • Deionised water.

    • Procedure

  • Take a small handful of grass from the same sample you took for the nitrates test.
  • Roll that sample into a ball and place it in the garlic crusher and squeeze down. Collect the grass liquid and place two to three drops on the refractometer. Read the brix number displayed on the refractometer. The sugar content should be 3% or higher.

    • Top tip

    Remember some local co-ops will test the sugars of your grass for free this season, or you can bring a sample to a lab to get tested. Just remember to take grass samples from across the field and cut the end of the grass with a scissors. Place it in a clean bag to transport to the lab.