Estimation of alfalfa fall dormancy using spaced plant and sward trials across multiple environments

Background:Alfalfa is a globally important forage crop.Cultivars are characterized by fall dormancy(FD).FD affects biomass yield and winter survival and is used to identify appropriate growing regions of cultivars.It has historically been assessed by measuring the natural height of regrowth in autumn of spaced plants in the field.Because commercial alfalfa is normally grown as a solid planted sward,FD could be different if plants were grown under real production conditions.The objective of this experiment was to assess whether FD ratings obtained from swards were similar to those obtained on spaced plants.Methods:We evaluated 20 alfalfa cultivars in field trials established in 2015 at five locations in the United States.We harvested the trials in early autumn and measured regrowth plant height approximately 3 weeks later in 2015 and 2016.Results:Autumn plant height responded as expected for the established check cultivars in all locations.Fall dormancy ratings for cultivars under both management systems were highly correlated.Conclusions:Estimating FD from spaced plant height measurements in autumn is very robust,and using height data from sward plots gives equivalent results to that measured in spaced plant nurseries.This finding has many practical advantages.