 |
ProCrop |
Frost Tolerance of
Ten Seedling Legume Species at Four Growth Stages
D. W. Meyer* and M. Badaruddin
Published in Crop Science: 41:1838-1842 (2001)
Abstract: Spring frost in cooler regions periodically kills seedling legumes and makes replanting necessary. Experiments were conducted in the growth chamber to determine freezing tolerance of 10 legume species at four growth stages and to determine the freezing temperatures that kill 50% of seedlings (LT50) for each species under temperature more commonly found in the field. Four temperatures (-2, -4, -6, and -8�C), four seedlings ages (1,2,3,and 4 wk after planting), and 10 legume species [alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), sweetclover (Melilotus officinalis Lam.), alsike clover (T. hybridium L.), white clover (T. repens L.), sainfoin (Onobrychis viciifolia Scop.), pinto bean (Phaseolus vulgaris L.), navy bean (Phaseolus spp.), soybean (Glycine max (L.) Merr.), and field pea (Pisum sativum L.)] were included. Hardened (vernalized) seedlings were placed in a programmable freezing chamber at 3�C and the temperature decreased or increased 1�C h-1 to or from a minimum-freezing temperature. Pinot and navy beans were the least tolerant, soybean and field pea were moderate, and forage legumes were the most tolerant to freezing temperatures. The LT50 was -3.25 to 3.5�C for dry beans, -4.5�C for soybean and field pea, and -6.3 to -7.4�C for forage legumes. One-week-old seedlings had the highest tolerance to freezing temperature when close to the LT50 compared with older seedlings. However, this tolerance at 1 wk of age disappeared when temperature was lower than the LT50 of the species. The prediction equation LT50 for each species have potential for predicting seedling stand loss after a spring frost, realizing that field validation of these is impossible.
The importance of Legumes as forage, grain, and oil crops in the northern Great Plains is well known. In addition to their cash value, legumes can be used to improve soil fertility and increase subsequent cereal crop productivity (Badaruddin and Meyer, 1990, 1994). One hazard in producing these crops is stand loss from spring frost, Frost in early spring periodically kills stands of legumes in cooler areas of USA and Canada (Brown and Blackburn, 1987). In 1998, dry edible bean was killed by frost on over 1200 ha in McLean County, North Dakota (Annu Res. Rep. No. 16,1998). A significant area of spring-seeded alfalfa, other forage legumes, soybean, and dry bean may be subjected to spring frost in this region.
Tolerance to freezing temperatures varies with multiple factors, and it is difficult to determine how much freezing damage is the result of temperature alone. A crop species may have tolerance varying with different growth stage, duration of freezing temperature, soil moisture, acclimation/declamation cycles, and other associated factors. Frost may cause damage at any age of the plant. For example, yield reductions from frost occurred from 0-R7 growth stages for two early maturing soybean cultivars in Canada (Saliba et al., 1982). Hume and Jackson (1981) evaluated 30 soybean geno-types of different sources and maturity groups at -2, -2.5, and -3�C at the cotyledon, unifoliolate, and first trifoliolate leaf stages. Prefreezing growth temperatures in the greenhouse were 15/9, 20/14, and 25/19�C (day/night). They found that the greatest soybean mortality occurred at the unifoliolate stage at -3�C when growth temperature in the greenhouse was 25/19�C compared with the lower growth temperatures. With exceptions, temperature drop in the spring does not occur abruptly in the northern Great Plains but over a 2- or 3-d period. The seedlings were not hardened in Hume and Jackson's (1981) experiments, temperature was dropped sequentially from the prefreezing to freezing over a 9.5-h period. but dropping the temperature from 9, 14, or 19�C at night to a freezing temperature within a 9.5 h generally does not happen in the northern Great Plains. A weather front could drop the temperature abruptly, but rarely does a freezing temperature occur the first night, which allows some seedling acclimation prior to freezing.
In another report, Hicks (1978) indicated that soybean was more tolerant to freezing temperature at the unifoliolate than at the third-trifoliolate leaf stage. However, plants from both stages could resume growth with 2 h after freezing at -3.8�C.
Seedling age is important for tolerance to low temperature. Calder et al. (1965) reported that legume seedlings were more susceptible to frost injury in the vegetative stage (up to 48d) compared with later stages. However, Peltier and Tisdal (1932) and Tisdal and Pieters (1934) reported that 2-wk and older seedlings were more tolerant to freezing than younger seedlings. None of these reports showed uniform survival rate of the seedlings at a particular temperature.
Many previous experiments (Megee, 1935, Steinmetz, 1926, Jung and Smith, 1961; Calder et al., 1966) have evaluated factors related to overwintering of forage legumes. Very few have evaluated spring-seeded seedling tolerance to freezing temperture. Arakeri and Shmid (1949) grew alfalfa, sweetclover, red clover, alsike clover, and white clover in the greenhouse at 20�C. Seedlings of different growth stages were hardened at 4�C for 15 d and then again at 10�C for 2 d in the growth chamber. Seedlings were held in the freezing chamber at -10�C for 8 h before transferring them to the greenhouse for 2 wk to obtain survival counts. Across the legume species, prefreezing growth stages represented by 1, 2, and 3 wk in the greenhouse (hypocotyl arch through 3- to 4-leaf stages) were more tolerant to freezing temperature than were older seedlings. However, survival percentage was more by the fourth week for alfalfa, and after the fifth week for alsike, red, and white clovers. Sweetclover seedlings younger than 9 wk did not survive the freeze. Their data suggested that the species and seedling age before influenced frost tolerance. However, the long hardening period used did not reflect typical northern Great Plain conditions where hardening period during the spring rarely exceeds 3 d, and rarely does the duration of minimum temperatures last for more than 1 to 4 h.
Calder et al. (1965) hardened alfalfa seedlings at 2�C for 48 h. They found that unhardened alfalfa seedlings were killed at -4.5�C temperature and did not regrow within two weeks. However, Tisdal and Pieters (1934) reported that about 90% of unhardened alfalfa and red clover seedlings survived at -4.1�C and no seedling death occurred with the hardened seedlings. In these experiments, they found that tolerance to seedlings to freezing temperature increased with hardening.
The threat of spring frost delays planting in many species. Delayed planting of dry bean may cause greater economic losses than does frost through the reduction of yield and quality seed (Blaylock, 1995). Delayed planting may also cause crop failure because of early fall frost. Although the risk of fall frost may be reduced by planting early in May, the risk of a killing spring frost is increased (Halvorson et al., 1995). Sims et al. (1989) reported that dry bean should be seeded as early as machinery can safely be used in the field in Montana. Each day of delay in seeding from 1 June to 7 June resulted in 29 kg ha-1 decrease in yield across four cultivars of pinto bean. They also suggested that even for warm-season beans, seeding should not be delayed beyond the first week of June for the crop to mature before the first killing frost in fall.
The limited studies evaluating freezing temperature tolerance of seedling legumes were conducted under hardening and temperature duration conditions usually atypical of that prevailing in the northern Great Plains during the spring. Therefore, our objectives were to determine freezing temperature tolerance of 10 legume species at four seedling ages simulating conditions more often prevailing in the field and to determine the 50% killing temperature (LT50) for each legume species.
Back to Spring Frost -
Environmental Damage Menu
Back to Environmental Damage Menu
Back to Main ProCrop Index
