Abstract: This research investigated the aboveground growth efficiency, together with belowground root morphological characteristics and spatial configuration for mixed plantings of the forages Avena sativa (As) and Vicia sativa (Vs), in trays of area 70 cm×45 cm, and 30 cm depth. The aim was to assess the competitive dynamics and the relative contribution of aboveground and belowground traits of the two species to the mixed cropping advantage in different plant spacings, and the nitrogen fixation, and nitrogen transfer and utilization efficiency of the different mixed cropping planting configurations, in order to clarify the inter-specific competition process. Four planting configurations with two monoculture controls were included in the experiment: As+Vs mixed within rows at 15 cm row spacing (T₁₅); As+Vs in alternate rows at 15 cm row spacing (Y₁₅); As+Vs in alternate rows at 15 cm spacing with a root barrier between (YZ₁₅); As+Vs in alternate rows at 30 cm row spacing (Y₃₀); monoculture As (CK₁); and monoculture Vs (CK₂). The results indicated that: 1) Forage yield was approximately 60% higher (P<0.05) for the T₁₅ and Y₁₅ planting configurations than for YZ₁₅ and Y₃₀, and this yield gain was reflected in higher land equivalent ratios (1.5, 1.4, 1.0 and 1.2 for T₁₅, Y₁₅, YZ₁₅ and Y₃₀, respectively). The aggressivity of As was substantially greater than that of Vs in all planting configurations. 2) The mixed cropping advantage of T₁₅ and Y₁₅ could be attributed partly to improved light utilization aboveground and partly to enhanced N fixation belowground and capture of legume-derived N by the more aggressive As. The relative contribution of aboveground and underground factors to the mixed-cropping advantage was about 22% and 78%, respectively. 3) Forage yield was positively correlated with the initial fluorescence efficiency (F) of the forage leaves and the capture of light energy per unit area (TR_o/CS_o) values (P<0.05). There was a significant positive correlation between forage yield and root morphological parameters and root configuration (P<0.01). 4) Because oats are strong competitors, they are also the main contributor to the advantages of mixed sowing. Therefore, in an environment of strong competition and high nutrient utilization efficiency, the T₁₅ and Y₁₅ planting configurations exhibited strong mixed planting advantages over CK₁ and CK₂, and LER ratios near 1.5.

Key words: mixed cropping, intercropping, growth efficiency, aboveground competitive patterns, root morphological and architecture characteristics, nitrogen use efficiency