The effects of moisture concentration and type on quality characteristics of alfalfa hay baled under two density regimes in a model system

Alfalfa (Medicago sativa L.) hay was packaged in laboratory-scale bales at nine moisture concentrations (250 to 358 g kg−1). Five concentrations were obtained from the field during initial dehydration, and four were obtained during the accumulation of dew at night. In the first study, bale density was increased as bale moisture increased (floating density; FD), thereby mimicking the confounded nature of these variables commonly observed with field-scale equipment. In the other study, this confounding was eliminated by maintaining a constant (400 kg/m3) dry matter bale density (constant density; CD), regardless of moisture content. Initial bale moisture was an excellent linear predictor of storage characteristics and changes in quality and was consistent for both the CD and FD studies. Moisture type (residual hydration or dew) had no effect on any response variable. Heating indices (degree days>30°C, degree days>ambient, mean heat generation rate, maximum temperature, and average temperature) were all effective in describing changes in artifact nitrogen concentration as linear functions during storage (r2>0.838). However, regression lines for FD and CD studies were dissimilar (different slope, intercept, or both) for all predictor variables except average temperature. The mechanisms that regulate heat damage to forage nitrogen during bale storage are complex. Although input factors such as moisture content, spontaneous heating, and bale density clearly impact final artifact nitrogen concentrations, their interactions are not understood fully.