Alfalfa Yield and Morphology of Three Fall-Dormancy Categories Harvested at Two Phenological Stages in a Subtropical Climate

Alfalfa (Medicago sativa L.) is the most important hay crop used in the dairy industry of the Po Valley, Italy, characterized by a subtropical climate with hot, humid summers and cool winters. Information is lacking as to selecting fall dormancy (FD) varieties adapted to the region and their response to intense harvest regimes. A 3-yr study was conducted to investigate the effect of two harvest regimes based on phenological stage (early bud and early flower) and three FD categories on productivity, canopy height, and leaf to stem proportion. 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, Italy. The experimental design was a randomized complete block in a split-plot arrangement. Canopy height and dry matter (DM) yield were measured at each harvest. Subsamples were collected to determine leaf area index (LAI), stem silhouette area index (SAI), and leaf dry matter to stem dry matter ratios (LSR). Nondormant cultivars had higher DM yield (18.2 Mg ha−1) than less nondormant (17.1 Mg ha−1) and very nondormant cultivars (16.9 Mg ha−1). Harvesting at early bud decreased DM yield by 11% compared to early flower. The FD categories had no effect on LAI/SAI and LSR ratios, however harvesting at early bud increased both ratios by 12.0 to 12.5%. Producers in subtropical climates may obtain alfalfa hay with a high portion of leaves at a reasonable yield from the three tested FD categories by cutting alfalfa at early bud stage.