Winter Annual Legumes for Use as Cover Crops in Row Crops in Northern Regions: II. Frost Resistance Study

Abstract

Several benefits, e.g., weed suppression, are achieved by including a cover crop in a cropping system. A requirement for developing cover crop systems in northern regions is to find species and cultivars which are adapted for the local climate. The basic objective of this study was to investigate the effects of freezing temperatures on subclover (Trifolium subterraneum L.) cultivars; however, because field experiments recently carried out in Norway have shown that subclover only has potential for winter survival near the southern coast, other winter annual legumes were also tested. To make an adequate freezing‐test program reflecting field conditions, a factorial experiment including cultivars, age of subclover plants, and daylength treaments was carried out. The study showed that frost resistance of subclover was increased by short‐day treatments both before and through the hardening periods. The effect of short‐day treatments was more pronounced for the early flowering cultivar Geraldton than for the later flowering cultivar Mount Barker. The freezing program developed for subclover may also be suitable for other winter annual legumes. The results of a winter annual legume experiment showed that hairy vetch (Vicia villosa Roth.) cultivars, especially cv. Hungvillosa, exhibited the best frost resistance, followed by yellow sweetclover [Melilotus officinalis (L.) Pall.], crimson clover (Trifolium incarnatum L.), black medic (Medicago lupulina L.), white clover (Trifolium repens L.), subclover, barrel medic (Medicago trunculata Gaertn.), and snail medic [Medicago scuttelata (L.) Mill.], which exhibited the poorest frost resistance. In terms of relative biomass, the hairy vetch cultivars Welta and Hungvillosa were significantly different at −9°C. In general, hairy vetch exhibited the best frost resistance in this study.