Fall Dormancy and Harvest Stage Impact on Alfalfa Persistence in a Subtropical Climate

Persistence of alfalfa (Medicago sativa L.) is a critical component of productivity and can be influenced by genetics and management; however the responses of fall dormancy (FD) level to harvest regimes are unclear. This study was conducted to investigate the effect of three FD categories and two phenologically based harvest regimes on stand persistence and characteristics of taproot and crown in a humid subtropical climate. Cultivars with FD ratings of 7.5 (less non‐dormant), 8.5 (non‐dormant), and 10.5 (very non‐dormant) were seeded in April 2005 at the experimental farm of Padova University in Legnaro, northeastern Italy. Plots were harvested at early bud or early flower for 3 yr and plant samples were collected in November 2005, April 2006, November 2006, April 2007, and November 2007. On each sampling date, stand density, mass of taproot (to a 15‐cm depth) and crown, water soluble carbohydrate (WSC) concentration of taproots and crowns, and taproot diameter at 3‐, 5‐, and 15‐cm depth were measured. Changing the cutting stage from early flower to early bud reduced the average stand density from 242 to 218 plants m−2, irrespective of FD category and date. In November, plants harvested at early bud had smaller taproots and crowns compared to those harvested at early flower but generally had higher concentrations of WSC. The implications of FD category appeared secondary in comparison to harvest regime to maintain alfalfa persistence in an environment characterized by temperate winters.