Fall Dormancy and Harvest Stage Effects on Alfalfa Nutritive Value in a Subtropical Climate

Alfalfa (Medicago sativa L.) annual yield is not strongly related to fall dormancy (FD) rating in regions with mild winters, but nutritive value might be, especially when accounting for harvest management. The objective of this study was to compare the forage quality of alfalfa having three FD ratings, all within the nondormant group, under the effect of two phenologically based harvest regimes in a humid subtropical climate. Cultivars with FD ratings of 7.5 (less nondormant), 8.5 (nondormant), and 10.5 (very nondormant) 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 from 2005 to 2007 and were subsampled at each harvest for nutritive value analyses. Differences were observed between FD ratings for weighted annual average (weighted by yield) neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), crude protein (CP), ash, and ether extract (EE). For example, less nondormant cultivars had higher CP (193 g kg(-1)) than nondormant cultivars (190 g kg(-1)), and very nondormant cultivars (187 g kg(-1)) Harvesting more frequently improved forage nutritive value regardless of the FD rating used. Alfalfa harvested at early flower had NDF concentrations 18 g kg(-1) higher than when harvested at early bud. All the chemical components studied were better correlated to the height of canopy than to the leaf to stem ratio (LSR). Results suggest that forage nutritive value was more impacted by stage of maturity than by FD rating or LSR.