A Simple Method for Estimating Alfalfa Fiber Content in the Field

Predictive equations for alfalfa (Medicago sativa L.) quality (PEAQ) based on length of the longest stem and maturity stage of the most mature stem in a sample were developed and validated for estimating neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations in alfalfa. The objective of this research was to validate PEAQ with a simplified maturity scale when estimating fiber content. Alfalfa samples varying in height and maturity were collected throughout the growing season from fields across six states in USA. Observed NDF and ADF values (determined via wet chemistry) were regressed on estimated values. The estimated values were calculated with PEAQ using the Kalu and Fick maturity scale (stages 2 to 6) and using a modified 3-stage scale consisting of vegetative stage (Kalu and Fick stage 2.0), bud stage (stage 3.5, i.e. averaged Kalu and Fick bud stages 3 and 4), and flower stage (stage 5.5, i.e. averaged Kalu and Fick flower stages 5 and 6). Regression equations for NDF and ADF were slightly biased (b 1.0 and/or y-intercept 0) for two of the three datasets regardless of the staging scale used. Prediction errors were similar regardless of the staging scale, ranging from 16.8 to 25.4 g kg-1 for NDF and 14.3 to 19.3 g kg-1 for ADF. We conclude that the 3-stage maturity scale can be used effectively in these equations for estimating alfalfa fiber content based on a combination of stem length and maturity