THE COMBINED EFFECTS OF RHIZOBIAL NODULATION AND NITROGEN-FERTILIZATION ON GROWTH AND COLD-ACCLIMATION OF ALFALFA (MEDICAGO-SATIVA CV SARANAC)

The combined effects of nitrogen fertilization and rhizobial nodulation on cold-tolerance of alfalfa were investigated. Inoculated and non-inoculated alfalfa plants were grown under different nitrogen fertilization regimes equivalent to 0, 25, 50 and 75 kg N ha-1. They were hardened at 2 °C for 4 weeks and submitted to a freezing-test consisting of 16 h at -1 °C followed by 3 °C decrement steps. In all nitrogen treatments, inoculated plants grew better than non-inoculated plants. There was no difference in nitrogen distribution within the plants among treatments. Nitrogen levels, but not nodulation, affected the capacity of the plants to harden. However, even the plants which were nitrogen-starved hardened, and mean differences between the more- and the less-hardened plants never exceed 1.1 °C. © 1991 Annals of Botany Company.