Effects of intercropping ratio on autumn-sowing oats/common vetch system on the Loess Plateau

Autumn sowed oats were intercropped with common vetch at different ratios in the rain-fed Loess Plateau, so that the effects on yield, leaf area index (LAI), light interception and soil nitrate content could be evaluated. Intercropping of oats with common vetch was carried out at ratios of 1∶0, 4∶1, 2∶1, 1∶1, 1∶2, 1∶4 and 0∶1. Results indicate that the ideal cutting time is between flowering and harvesting, and that the best mixture rate is 2∶1 or 1∶1. At vetch flowering, The highest yield of 3 264 kg·ha-1 occurring at a mixture rate of 2∶1, followed by 2 828 kg·ha-1 at a mixture rate of 1∶1, producing 30% and 13% more yield than monocultured oat respectively. The highest yields at harvesting were 5 942 kg·ha-1 under mixture rate of 1∶1 and 4 980 kg·ha-1 under mixture rate of 2∶1, which respectively produced 50% and 30% more yield than monocultured vetch. The highest relative total yield at flowering was 1.39 (2∶1 mixture rate), followed by 1.24 (1∶1), which indicates that the land use efficiency under this intercropping program was improved by 24%~69% when compared with monocultured oats. There was no significant difference observed in canopy leaf area index, light interception and soil nitrate content between intercropping mixture rates, which suggests that there was no competition for light and that the nitrogen fixation ability of legumes was not demonstrated during the intercropping experiment. This result may be related to “nitrogen repression” caused by a large amount of fertilizer applied at sowing.