On-Farm Moisture Testing of Corn Silage
determining corn whole plant moisture is important when harvesting for
corn silage. Harvesting corn for silage too early (high moisture content)
or too late (low moisture content) can affect forage yield, quality and
plant moisture content typically changes by 0.5 units per day and in dry
conditions can change by up to 1.0 unit per day. In the past, growers have
used benchmark stages of kernel maturity (black-layer development or
kernel milkline position) to estimate when to harvest corn for silage.
Because of the variability associated with these methods, growers have
been encouraged to periodically check actual whole plant moisture of
plants from various fields on their farm. The success of this strategy is
dependent on obtaining an accurate moisture content measurement in a
Focus on Forage article discusses the accuracy of several on-farm
moisture measurement techniques based on a study conducted by the UW Soil
& Forage Analysis Lab at Marshfield.
affect moisture content of corn plants and the rate at which they dry down
in the field.
What factors affect
measurement of whole plant moisture content?
measuring corn whole plant moisture the following factors can affect the
accuracy of the test.
What moisture measurement methods were compared?
What did the study show?
In a lab setting, approximately 2% residual moisture content was found in samples after using the microwave or Koster drying methods. Another study conducted on-farm using several different operators, showed that residual moisture content ranged from 3% to greater than 6% (Ballweg and Rankin, 1998; Figure 1). Error levels of this magnitude are unacceptable for growers needing to make a corn silage harvest decision.
All methods require an additional laboratory step to determine residual moisture content of a sample for complete accuracy. This can be accomplished using either a NIRS-based moisture determination or a standard high temperature (135oC) lab oven method.
Fineness of Chop
Sample grind and fineness of chop is important in determining sample moisture content. This is particularly important when using the microwave drying method. The variability among samples was higher for coarsely chopped samples when compared to those ground to a smaller particle size. In addition, the moisture remaining after drying was greater for coarsely chopped samples versus using a fine grind (Figure 2).
drying method affected the variability of moisture determination.
Specifically, the microwave method was more variable than the Koster
drying method was, while the laboratory oven method was least variable
Effect of drying method and number of
operators on residual moisture content of corn silage samples.
Effect of drying method and grind type on
residual moisture content of corn silage samples.
Accurately determining the moisture content of corn silage on the farm is a difficult process. One of the limitations to on-farm testing is the availability of an accurate scale (+/- 1 gram). In addition, operators need to maintain a consistent protocol when drying samples so that the residual moisture content is consistently in a range of 2-5%. Finally they need to have a laboratory determine the average residual moisture content of dried samples.
If the on-farm test would consistently result in 2-3% residual moisture when calibrated with a laboratory result, the operator could then make reasonable management decisions about when to harvest corn for silage.
A better option is to submit samples to a laboratory for dry matter analysis. Using a laboratory greatly reduces sample-to-sample variability and results in a more accurate number.
Ballweg, M. and M. Rankin. 1998. Verification of On Farm Moisture Determination.