Seed production and seed survival under grazing of annual medics (Medicago spp.) in north Syria

Abstract

SummaryThree experiments which measured seed production and seed survival of annual medics (Medicago spp.) were conducted at Tel Hadya in north Syria. In Expts 1 and 2, conducted in consecutive years, the effects of rate and date of sowing on seed yield and its components were measured, while in Expt 3, the residual seed under summer grazing was monitored. In all three experiments seed permeability was observed at frequent intervals in summer and autumn. Selected ecotypes of three native medics (Medicago rigidula (L.) All., M. rotata Boiss. and M. noeana Boiss.) were compared with cultivars of M. truncatula Gaertn. and M. polymorpha (L.).Seed production was greatest at sowing rates of 20–40 kg/ha. The native species produced more seed (up to 1000 kg/ha) than the cultivars (less than 500 kg/ha), although not significantly so in the case of the late-flowering ecotype of M. noeana. Seed yields of 500–1000 kg/ha were considered to be sufficient to perpetuate the pastures, but even higher seed yields are desirable.Seed yield was closely related to number of pods in all ecotypes and, in Expt 2, up to 95% of flowers failed to produce mature pods. Flowers were more likely to mature at high sowing rate (256 kg/ha), in striking contrast to flower production itself which was greatest at sowing rates of less than 30 kg/ha. Flowers produced early in the season (before mid-April) were far more likely to give mature pods than late-produced flowers.In late October, seeds of the native species were less permeable (10%) than those of the cultivars (30%), although their permeability was similar to that of the cultivars in Australia. In the three experiments the seasonal pattern of permeability varied, although there was a tendency for seeds to gain permeability in autumn. In Expt 1 there was a strong suggestion that the change from impermeability to permeability was reversible.Ewes grazing mature pods gained weight, apparently as long as pod availability exceeded 10 kg/ha. It was clear that the condition of ewes was not a good guide to appropriate stocking rate for persistence of pastures, and that farmers will have to use other methods to assist them in grazing management.