Quantifying winter survival of alfalfa [Medicago sativa (L.)]

Winter injury of alfalfa [Medicago sativa (L.)] in the northern United States decreases its economic and ecosystem benefits. Therefore, continued improvement in alfalfa cultivar winter survival (WS) is crucial for sustaining the productivity of this perennial crop. The North American Alfalfa Improvement Conference (NAAIC) standard test for WS recommends measuring the WS of spaced plants established in rows the previous spring. Measurement of WS of alfalfa grown in sward plots used by plant breeders would increase data collection and better reflect the potential for WS when grown in production fields. We conducted trials at seven location-year environments spanning from Wisconsin to South Dakota in the northern United States. These trials involved six check cultivars and followed protocols from the NAAIC standard test. The objectives were to determine (1) if WS and biomass yield assessment from sward plots were similar to those from the standard spaced planted row ratings and (2) if location-dependent environmental conditions affected the usefulness of alternative approaches for measuring WS. Estimation of WS using spaced plants and sward measurements was highly correlated, while correlations between the WS of the spaced planted rows and biomass yields were less. The number of locations required for spaced and sward plantings to determine cultivar differences was at least two, with four replications per location. Measuring WS from swards can enhance data collection and its relevance to on-farm alfalfa production, as sward plots serve a dual purpose by allowing both WS testing and evaluation of yield, making them a practical choice in comparison to the exclusive use of spaced plants in rows for WS testing. Availability of sward-plot WS descriptions of alfalfa cultivars will enhance decision making by producers.