On the frost resistance of red clover with special attention to seed production

Authors

• Arvi Valmari Agricultural Research Centre, Frost Research Station, Pelsonsuo
• Irja Valmari Agricultural Research Centre, Frost Research Station, Pelsonsuo

DOI: https://doi.org/10.23986/afsci.71650

Abstract

The frost-resistance of Finnish red clover has been studied by means of experiments in a cold cabinet and on the basis of samples taken from the field. In the cold cabinet experiments the frost injury of the clover plant’s vegetative parts has reached considerable magnitude when the temperature was about 4° C. Also the unripe heads which did not die immediately could suffer so that the development of the seed stopped. Definitive death of the plants began to occur in the treatment at 5° C, though only when the soil was frozen. The plants recovered after treatment at 10° C if the soil was not frozen. In the field little frost injury of the vegetative parts occurred even with a frost of 6 to 7° C, but the unripe seeds suffered injury in that case. The germination percentage is distinctly dependent on the seed size in absence of frost. The stage of development at which more than 70 % of the corollae are light brown constituted an intermediate phase where the variation in germinative ability was great and covered, when the samples subjected to slight natural frost (–6.6° C) were taken into account, practically the entire per cent range (0—99 %). After the corollae of the heads had turned dark brown, at which time the seed had reached full weight, the seed suffered no injury from –6 to –7° C frost, and even more severe frosts could at the most cause a very slight lowering of germination percentage. Frost seems to injure the seed mainly by stopping the development of the unripe seeds. No lowering of germination from the level corresponding to the seed size has been observed in all cases nor was there any complete loss of germinative ability such as occurs with cereals. The commercial value of frost-injured red clover seed can be considerably increased by sorting. The number of hard seeds is highest in large, early harvested seed. Frost evidently causes »softening» of germinative seeds. The risk implied by frost is less in clover seed cultivation than in the cultivation of spring cereals and potatoes.