FORAGE YIELDS AND QUALITY OF COMMON VETCH AND OAT SOWN AT VARYING SEEDING RATIOS AND SEEDING RATES OF VETCH

In the Mediterranean area, most annual legumes, such as common vetch ( Vicia sativa L.) that have a scrambling habit, are sown with oat (Aven a sativa L.) to improve growing conditions and forage harvesting. Alth ough some studies have examined the effects of varying seeding ratios, the optimum seeding rates for those combinations are not well-defined . The objective of this study was to compare the yields from mixed sta nds of vetch (principal species) and oat (secondary species) obtained when several seeding rates of vetch were combined with various seeding ratios of the two species. A field study was conducted at two locatio ns near Madrid in the 1981-82 and 1982-83 growing seasons. Both specie s were planted as monocrops and in mixtures. Ratios of the number of v etch to oat seed were 100:0; 90:10; 80:20; 70:30 and 60:40. Within eac h mixture, seeding rates of vetch were 60, 80, 100 and 120 kg ha-1. Th e oat monocrop was seeded at 140 kg ha-1. Plants were harvested at the pod-setting stage of vetch. Relative yield total (RYT) calculated as the sum of the relative dry matter yields of both species was used as the criterion for mixed stand advantage. Mixtures produced 34% more dr y matter than the monocrop of vetch, but 57% less than the oat monocro p. Dry matter yields of mixtures were not affected by seeding ratio or seeding rate of vetch but proportions of vetch dry matter decreased l inearly as the percentage of oat seed in the mixture increased. The ne t effect of oat in the mixture was a linear increase in competition as oat density increased. Relative yield totals of mixtures with 90:10 o r 80:20 ratios of vetch:oat seed exceeded unity.