Electrical resistance of high-moisture chopped alfalfa

The goal of this study was to characterize the relationship between electrical resistance (R-F) of fresh or partially dried chopped alfalfa and its moisture content. Crop temperature, pressure applied against the forage, and time-dependency were also assessed. Freshly chopped alfalfa was dried in ambient air to obtain moisture content (M) at ten levels in the range of 49% to 82%. After freezing, a six-month storage period, and thawing, alfalfa was conditioned at three levels of temperature (T), approximately 5 degrees C, 20 degrees C, and 35 degrees C. Three samples at each M and T were placed in a test cell where five pressure levels between 3 and 28 kPa were gradually applied. The electrical resistance between two electrodes spaced 55 mm apart was measured by generating a 10 VDC potential during 60 s after a previous 60 s stabilization period at each pressure level. In the experimental range, log(RF) decreased by 1.5% on average for each 1% unit increase of moisture content. Meanwhile, log(R-F) decreased by 0.35% on average for each 1 degrees C increase in temperature. The best prediction model had an R-2 = 95.7% and was based on measurements taken 0.5 s after the application of voltage and for a pressure level of 21.6 kPa against the forage. Resistance increased between 0.5 and 5 s after application of voltage, especially for low water concentrations (< 300 kg water m(-3)). Resistance was stable over the entire time (0.5 to 60 s) for high water concentrations.