Maize for Silage
Technical
Insight 314

MICROWAVE DRYMATTER TESTING OF MAIZE SILAGE

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EQUIPMENT REQUIRED

  • Accurate scales.
  • Glass of water.
  • Microwave safe plate or paper plate.
  • Table fork.
  • Pen & paper for recording.
  • Calculator.

Steps

  1. To obtain a representative sample, take several plants from different places that are more than 20 rows from the edge of the crop. These plants should be chopped into 15 mm pieces. If the material is already stacked, take 10 handfuls of silage from a part of the face that has just been exposed. Mix the handfuls thoroughly so that a good subsample may be taken. To obtain an accurate sub-sampling of the material it is recommended the quartering method be used. To do this, place the material that is to be sub-sampled on a flat surface in a circle. Use a ruler divide the sample into four, and discard two of the sections. Mix the remaining two portions together and repeat procedure until you have the desired amount of sample (100 - 200 g) remaining.
  1. Weigh a microwave safe plate or a paper plate to obtain a “tare” weight, remembering to ensure the paper plate is “dry” by leaving it in the microwave for short periods to remove moisture from the plate. Check weight of plate after each period in the microwave until there is no change in the weight of the paper plate.
  1. Weigh between 100 - 200 grams of the sample on a small accurate scale. This is the wet weight.
  1. Place the sample on a shallow plate that is suitable for use in a microwave oven.  Spread in a thin layer.
  1. Put a half full glass of water in the back corner of the microwave oven. Keep the water level constant during microwave use.
  1. Place the sample in the microwave oven for 3 - 4 minutes. If the forage feels almost dry, weigh it and record the weight. Stir the sample using a fork, rotate the plate and then put the sample back into the oven for 1 minute.
  1. Continue procedure no. 6 reducing the time to 30 seconds until drying does not reduce the weight more than 2 grams or the sample begins to char. If charring occurs, use the previous weight for calculating moisture content. Dry weight is the last recorded weight after which the sample does not decrease more than 2 grams and charring has not occurred.
  1. To calculate the percentage drymatter, divide dry weight by wet weight.  Multiply this by 100.

Example
Wet weight                                                                                      = 200 grams

Dried for 4 minutes – weight                                                       = 70 grams

Dried for an additional 30 seconds – weight                            = 64 grams

Dried for an additional 30 seconds – weight                            = 63 grams

                           

Wet weight = 200 grams

Dry weight = 64 grams

Drymatter = (64 grams divided by 200 grams) X 100 = 32%

 

Please note: Microwave oven power varies greatly from unit to unit and for this reason there may be variation in drying times. With practice, the procedure can be quickly and accurately established.

 

 



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Revised: June 2015
Expires: June 2018