Preharvest neutral detergent fiber concentration of alfalfa as influenced by stubble height
Regression equations can be used to estimate the preharvest neutral detergent fiber (NDF) concentration of alfalfa. In New York, where the stubble height of alfalfa varies due to terrain, predictive accuracy of existing equations may be reduced. The objectives of this experiment were to develop and evaluate alfalfa NDF equations that incorporate intended stubble height. Stands of first-cut alfalfa were sampled in producers' fields in New York in 2007, and cut into 5-cm segments. Predictive NDF equations were developed for each segment and for the whole plant. To develop whole-plant equations, it was necessary to develop and use equations describing the change, with alfalfa height, in the contribution of each segment to the overall dry matter (DM). The r2 values ranged from 0.90 to 0.93 for the individual segments and 0.93 for the whole-plant equations. The whole-plant equations performed comparably to existing models when evaluated using a dataset of 109 alfalfa samples cut at 10 cm, from 19 New York counties in 2004 and 2005. The derived equations were also fitted to samples collected at a range of stubble heights from New York and Minnesota in 2008. For the New York dataset, the r2 values for whole-plant equations ranged from 0.86 to 0.87, compared with 0.66 to 0.68 for existing equations, which were also biased. The r2 values for the Minnesota dataset were also high, but with some translational bias. The equations could be used by New York producers to obtain a more accurate estimate of preharvest NDF concentration.