One of the most important steps to make good silage is to cut it at the proper moisture level. The optimum moisture range for cutting corn and making silage is between 60-70% moisture (30-40% dry matter). Given the genetics of today’s corn varieties, utilization of the old relationship between the milk line and plant moisture content may not always be accurate.
An easy, quick and relatively inexpensive method to determine the actual moisture content of the whole corn plant is using a microwave oven. One additional advantage is that it takes typically less than 20 minutes to run the test.
So what equipment will you need to facilitate the moisture test?
- Microwave, with a turntable (preferably). Your wife or significant other will appreciate you NOT using the kitchen microwave or doing this in the house kitchen, as it does produce an unpleasant odor. It is thus recommend to have a microwave in the shop or barn to run the moisture test.
- Scale, one that weighs in grams is best.
- Container, something that is microwave safe such as paper plate, paper boat, or a glass or plastic dish.
- Water – 8 oz glass to protect the microwave oven
- Paper & Pencil to record weights
Next you need to collect a sample. Collect at random 10-20 plants throughout the field. You will need to chop these plants and this can be done by either shredding them in a brush chopper/branch shredder or by running them through your chopper. Please keep in mind that this can be a very dangerous process and care should be taken when doing this. The other option is to chop test areas in your field. Then take random grab samples from the green chopped silage. You should have about 2 gallons worth of product to mix and collect your test sample from. Once you have collected a representative sample you can start the process to run the moisture test.
Follow these steps to determine the moisture content of your corn silage or forage. Please note that this method can also be used to determine moisture content in any other forage.
Microwave Moisture Testing of Forages
- Take your gram scale and weigh the container you will use to hold the sample. This weight is known as Value A.
- Mix your sample and place about 100 grams in the container. Collect the total weight of the container and wet sample, record the weight as Value B.
- Put an 8oz. glass of water in the corner of the oven.
- Put the container with the sample in the microwave oven. Using a medium to high heat setting start drying the sample, starting with approximately 3-4 minutes if you suspect the sample is above 35% moisture.
- Remove the container and sample, weigh them, and record the weight. It should weigh less than the Value B that you initially recorded.
- Gently stir the sample and place back in the microwave.
- Reheat the sample again for another 30 seconds. Remove, reweight, and record the weight. You should continue this process, recording the weight every time. (You will need to be careful not to char or burn the sample. If you do, then either start over or take the previous recorded weight prior to charring the sample. You do not want your sample to be charred, so a hint is to go in time increments of less than 30 seconds once you feel your sample is getting close to dry.)
- Once you have two continuous weights that are equal, the sample is considered dry. Record this final weight as Value C.
Lastly you will need to calculate the percent moisture using the following formula:
- Value A = weight of container
- Value B = weight of container + initial wet sample weight
- Value C = weight of container + dry sample weight
Producers need to remember that if the silage is too wet there is a risk of butyric acid forming and nutrients being lost due to seepage. Silage that is over 70% moisture should not be harvested and should stand in the field for a few more days. On the other hand if it is too dry it will not ferment or pack adequately resulting in mold development. You may then need to add water to get an adequate pack and fermentation process. Therefore, having an accurate determination of what your corn silage moisture is running is critical in putting up good silage in a timely manner.