Restoring ecosystems in the southeastern United States by interseeding alfalfa in existing cool-season grass pastures

The introduction of legumes such as alfalfa (Medicago sativa L.) into forage systems is a sustainable alternative to pasture restoration by adding biologically fixed N and contributing to the biodiversity of the system. Also, crabgrass (Digitaria sanguinalis L.; [CG]) is known as a grass weed but has the potential to maintain forage mass (FM) during the summer contributing to restoration. Different experiments were carried out in Spring Hill, TN for 2 years each in tall fescue (Schedonorus arundinaceus [Schreb.] Dumort; [TF]) or orchardgrass (Dactylis glomerata L. [OG]), with the addition of alfalfa and CG. For each grass sward, two separate pastures were selected, and treatments were established in different years, totaling four different experiments [two Establishments (EST 1 and EST 2) for TF and OG]. The treatments imposed were (1) control (C), (2) synthetic N fertilization (SNF), (3) fall seeding of alfalfa (FA), (4) spring seeding of alfalfa (SA), (5) fall seeding of alfalfa + CG (FA + CG) and (6) spring seeding of alfalfa + CG (SA + CG). Each experiment had four replications totaling 24 plots each, and measurements included botanical composition and FM. In the TF pastures, there was no presence of alfalfa documented (0%), and little CG was detected, due to its high competitiveness; meanwhile, FM was only increased when N fertilization was used in EST 2, 3391 kg DM/ha. The average FM for all treatments in EST 1 was 2476 kg DM/ha. The OG pastures showed the presence of both alfalfa and CG in their botanical composition, with N fertilization also showing higher FM (EST 1, 2705 kg DM/ha; EST 2, 2390 kg DM/ha). Thus, alfalfa and CG have the potential to improve OG swards, but more research is needed to assess different establishment methods of alfalfa into TF swards.