Abstract:

The ratio of seeding rates in mixed sowings of legumes and grasses is a key factor affecting the yield and quality of mixed grassland. This research investigated the optimal ratio of mixed sowing seeding rates for oat and common vetch in the Ningxia Yellow River Irrigation Area. Six treatments were set up： Four ratios of oat and common vetch ［A₅V₅ （5∶5）， A₆V₄ （6∶4）， A₇V₃ （7∶3） and A₈V₂ （8∶2）］ together with oat and common vetch monocultures， to investigate the production， interspecific competition and nutritional value of the two monocultures and their combinations. It was found that the annual hay yield of the mixed treatments ranged from 14.84 to 17.62 t·ha^-1， which was 4.53% to 24.10% higher than that of oats sown alone and 64.03% to 94.75% higher than that of common vetch sown alone. The A₈V₂ treatment had the highest annual hay yield （17.62 t·ha^-1）， which was significantly higher than that of the single sown and A₅V₅ treatments. The treatment A₆V₄ had the second highest trial yield of 16.61 t·ha^-1. The land equivalent ratio of all mixtures was greater than 1， indicating that the mixtures improved land use efficiency. Interspecies disturbance was less than intraspecies disturbance， and oat and common vetch showed a synergistic relationship， whereby the highest land equivalent ratio of 1.30 was found in the A₈V₂ treatment， indicating that this treatment had the greatest benefit in terms of increased yield. The relative yields of oat were all greater than those of common vetch in the mixed treatments. The aggression intensity of oat was greater than 0 and the competition ratio of oat was greater than that of common vetch， indicating that the aggression of oats was greater than that of common vetch and that oat had a competitive advantage. Regarding the nutritional quality of the forage， there was no significant difference between the mixed treatments. However， A₅V₅ had the numerically highest nutritional quality and A₆V₄ had the numerically highest crude protein yield （1.90 t·ha^-1）. Overall， mixed cropped oat and common vetch had the highest yield， land equivalent ratio， system productivity index （8.94） and net annual income （16418 yuan·ha^-1） with the A₈V₂ mixture. Therefore， it is recommended that oat and common vetch mixtures planted at a ratio of 8∶2 should be promoted in the Ningxia Yellow River Irrigation Area.

Key words: oat, common vetch, mixed grassland, production performance, interspecific competition