The winterhardiness of alfalfa species and cultivars.
The winterhardiness of 134 alfalfa cultivars from 20 different countries was investigated in 4 field trials at Jõgeva Plant Breeding Institute (58°45' north latitude, 26°24' east longitude, the yearly average air temperature 4.4°C, precipitation 655 mm) during 1982-1990. The investigation included 63 cultivars of the species Medicago sativa L.
, 68 of Medicago media Pers.
, 2 of Medicago falcata L.
and 1 of Medicago borealis L.
The vast majority of the cultivars' seeds originated from the gene bank of VIR. Research was carried out in spaced-plant plantation (90×90 cm), the winterhardiness of cultivars was assessed on the basis of plants' survival.
Minimal air temperature and the sum of mean diurnal negative air temperatures (in the presence of sufficient snow cover) were not the reasons for bad winter survival during the conducting of the trials. A lot of alfalfa plants were lost winters with sudden and large temperature fluctuations. Heat waves occurred in December and January during these years when the air temperature rose to 4-6°C and it was raining. The shallow soil layer thawed, saturated with melted snow and ice, and later on an ice crust formed.
The winter survival of red clover in tame hay swards (assessed with suffusion) and that of alfalfa were not always similar in Jõgeva. The winters occurred when red clover had satisfactory winter survival in Estonia and alfalfa overwintered well in Jõgeva and vice versa.
As was also the case in several previously published research papers in Estonia we had to experience the unreliability M. sativa L. cultivars of southern origin in Estonian climatic conditions. Only in very favourable wintering conditions during the first hibernation did their sward maintain the necessary density for considerable yield capacity.
Cultivars of M. media Pers. had better winter survival than those of M. sativa L. in the trials. There were 19 foreign cultivars among the former ones (18 originating Commonwealth of Independent States (CIS), 1 of Canadian origin), winterhardiness of which turned out to be good (60-80% of the plants survived until the end of the growing season of the third year of use) or excellent (80-100% of the plants survived until the end of the growing season of the third year of use) in Estonian conditions. On the basis of the trial results so far, the economic traits of the following M. media Pers. cultivars should be checked in state testing: 'Kamalinskaya 930' (86.7% of the plants survived the autumn of the third year of use in Jõgeva), 'Marusinskaya 425' (84.2%), 'Barnaulskaya 171' (83.8%), 'Kamalinskaya 530' (80.0%), 'Taezhnaya' (79.2%), 'Zabaikalka' (79.2%), 'Omskaya 8893' (77.1%), 'Biiskaya 3' (75.4%), 'Oranzhevaya 115' (74.2%), 'Zheltogibridnaya 99' (70.0%), 'Kazanskaya 64/95' (69.6%), 'Iskra' (67.5%), 'Karatshinskaya' (67.5%) and 'Kazanskaya 36' (66.7%).
The tested cultivars of M. falcata L. and M. borealis L. revealed good or excellent winterhardiness but their yield capacity is lower than that of M. media Pers. cultivars.
Considering that Estonian soils are sporadically very stony and that machinery and energy have become several times more expensive, it would be reasonable to test the cultivars of variegated and yellow-flowered M. media Pers., M. falcata L. and M. borealis L. separately in state testing. The State Variety List can be kept in a respective way. The current testing order, after which the yield of the three years of use is determined, does not expose the advantages of these species (hybrids) arising from their different longevity.