Entry x environment interactions for alfalfa forage quality

Alfalfa (Medicago saliva L.) cultivars are available that produce high-quality forage; however, information is lacking on the consistency of cultivar forage quality over environments and the influence of stand age on quality. Our objectives were to evaluate alfalfa cultivars for consistency of forage quality over time and environments and to test the validity of sampling seeding-year stands for forage quality. We sampled eight alfalfa entries (seven cultivars and one experimental germplasm) at bud and flower maturity stages in the seeding year (one harvest) and first production year (two harvests) in six states (Indiana, Kentucky, Minnesota, New York, Washington, and Wisconsin). ANOVA and orthogonal contrast analyses were conducted to assess entry x environment interactions for forage quality. First-cut forage in the first production year had lower forage quality than thirdcut forage, and differences between entries were more pronounced at the first cutting. Including seeding-year data in the ANOVA produced a complex location x entry x stand age interaction, indicating that seeding-year data alone were insufficient to characterize alfalfa entries for forage quality. 'Cimarron VR', 'Arrow', and '5432' had the greatest stability for forage quality and could serve as high, medium, and low forage-quality checks, respectively, in forage quality testing trials. 'WL 322 HQ' and 'Pacesetter' often had high quality, but were not stable for forage quality over environments. Correlations between crude protein, acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro digestible dry matter were consistent across locations, entries, cuttings, and maturities. The high correlation between NDF and ADF (r ≥ 0.97, P ≤ 0.05) suggests that it may not be necessary to use both procedures to predict entry differences in forage quality.