Dry Matter Yield and Stem Nutritive Value of Six Alfalfa Cultivars Under Two Irrigation Conditions In Southern High Plains, U.S.A.

Alfalfa is the main legume for forage production in the U.S.A. The objective of this study was to determine if alfalfa selection for drought tolerance has an impact in stem nutritive value. Three alfalfas selected for drought tolerance and three commercial were planted in 2009 at two irrigation conditions, normal irrigation (NI) and limit irrigation (LI) under a randomized complete block design. In 2010, NI and LI were harvested five times. From the first three harvests a 100-g subsample was taken from each entry and separated into leaf and stem. Stem samples were analyzed for crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and NDF digestibility (NDFD). Whole plant dry matter (DM) yield was not different among entries on neither NI nor LI (P > 0.05), except NI at first harvest (P < 0.05). When averaged across three cuts, DM yield under NI condition was numerically higher in NM312 (4.06 Mg/ha/cut), while under LI Pioneer 56S82 had greater DM yield (3.60 Mg/ha/cut). There were no differences (P > 0.05) in stem quality parameters among alfalfa entries in NI, but there were in LI (P < 0.05) in two of the three cuts. Averaging across three cuts in LI, CP concentration was greater in Ameristand802 (120.3 g/kg), Pioneer 56S82 (119.7 g/kg), and WL-535 (118.4 g/kg) than in Dona Ana (116.7 g/kg), NM307 (114.6 g/kg), and NM312 (109.4 g/kg). In contrast, NDF and ADF concentrations were greater in NM312 (598 g/kg and 476 g/kg, respectively) and NM307 (593 g/kg and 468 g/kg, respectively) than Dona Ana and the three commercial entries. The NDF digestibility was not different among entries in either irrigation condition (P > 0.05). Results indicate that stem nutritive value in two of the drought tolerant germplasms was affected under LI conditions.