To make good silage from summer annuals such as sorghum, sudangrass, and pearl millet, the dry matter concentration should be between about 30% to 40% (moisture contents of 60 to 70%). Silage made wetter can seep which causes a loss of nutrients and potential environmental damage if the seepage gets into surface water (fish kill). Silage made drier will not pack adequately and may heat during storage. In some situations, heat generation can be great enough to start a fire within the silage mass. The drier the silage, the greater the risk for a silo fire. In addition to DM, chopping length of particle size of the chopped forage affects heating risk. Coarsely chopped silage does not pack as well as finely chopped silage, but silage chopped too finely can cause rumen upsets when fed to cattle. Choppers differ but setting the theoretical length of cut (TLC) at about 3/8 to ½ of inch will usually produce the correct particle size. Chop length needs to be reduced as the DM at chopping increases.
Measuring Dry Matter
1. Obtain a good sample. The dry matter of leaves will be much greater than that of the stems and the lower portion of the stem will be wetter than the top. The sample must include the total plant that will be chopped. Go into the field (not outside rows) and hand cut 5 to 10 plants at the same height that the crop will be mowed. Chop all the plants using a wood chipper, forage chopper, or by hand.
2. Mixed the chopped sample well.
3. Measure dry matter using one of the methods below.
Koster Tester (Koster Inc., Brunswick OH)
Follow manufacturer directions, but basically you need to accurately weigh out about 200 grams (0.5 lbs.) into the drying container. Record the weight. Dry for about 20 minutes and re-weigh and record the weight. Dry another 5 minutes and weigh again. If weight is the same as the 20 minute weight, the sample is dry. If not, repeat drying in 2 or 3 minute intervals until weight is constant. Calculate DM% as (Starting weight – Ending weight)/Starting weight x100. Moisture = 100 - DM%.
Accurately weigh about 100 grams (0.2 lbs) of chopped forage on a paper plate. Record the weight. Spread it out thinly. Fill a microwave safe mug about half full with water. Put plate and mug into a microwave. Heat on full power for 2 minutes, remove plate, weigh, record the weight and stir the forage. Heat for another 30 seconds, remove, weigh, stir, and record weight. Repeat the 30 second cycle until weight stabilizes. Watch carefully because it can catch fire. It usually takes about 4-6 minutes. Calculate DM% as (Starting weight – Ending weight)/Starting weight x100. Moisture = 100 – DM%.