Supplemental Irrigation and Fall Dormancy Effects on Alfalfa Productivity in a Semiarid, Subtropical Climate with a Bimodal Precipitation Pattern

Abstract

Alfalfa (Medicago sativa L.) is an important hay crop produced under rain‐fed conditions or various levels of irrigation in the southern Great Plains of the USA. The objective of this study was to determine the role of fall dormancy (FD) on productivity and forage nutritive value of alfalfa in rain‐fed and supplemental irrigation systems in a semiarid, subtropical climate with a bimodal pattern of precipitation. Cultivars with FD ratings of 1 to 3 (dormant), 4 to 6 (moderately dormant), and 7 to 8 (nondormant) were planted in November 2001 on a Miles fine sandy loam (fine‐loamy, mixed, Thermic Udic Paleustalfs) near Vernon, Texas in two adjacent, randomized, complete‐block experiments representing rain‐fed and supplemental irrigation systems. In the supplemental irrigation system, water was supplied during April to October to meet the long‐term average monthly precipitation. During 2002–2005, plants were defoliated to 5 cm height at 5 to 15% bloom in all cultivars. In the rain‐fed system, FD had no effect on productivity (5.6–6.0 Mg ha−1). Nondormant cultivars produced higher dry matter yield (20.2 Mg ha−1) than dormant cultivars (15.9 Mg ha−1) under supplemental irrigation. Moderately dormant cultivars were intermediate (18.6 Mg ha−1). Forage nutritive value was greater in the spring (rain‐fed) or spring and autumn (supplemental irrigation) than in the summer. Weather patterns and harvest time interacted with FD in determining forage nutritive value under supplemental irrigation. Cultivars with FD ratings of 5 to 8 may be used in similar environments of the southern Great Plains to maximize productivity of alfalfa.