Abstract: We examined the effects of intercropping on crop stability under different ratios of nitrogen forms with a wheat (Tricum aestivum) and faba bean (Vicia faba) intercropping system. A pot experiment was designed under treatments with different ratios of nitrate and ammonium nitrogen including nitrate nitrogen alone (N1), nitrate∶ammonium=1∶3 (N2), nitrate:ammonium=2∶2 (N3), nitrate∶ammonium=3∶1 (N4), and ammonium nitrogen alone (N5). We analyzed crop yield increase (OY), aggressivity (A_WF), relative interaction intensity (RII), interspecific compatibility (RYT) and productivity stability of intercropping system by measuring crop biomass under different cropping conditions. The results showed that wheat biomass was increased under intercropping compared with monocropping. Intercropping wheat biomass was increased by 86.0% than monocropping under N2 treatment (P<0.05). A_WF of wheat was greater than 0 and RYT was greater than 1 under different nitrate and ammonium nitrogen ratios. The maximum values of A_WF and RYT were reached under N2 treatment. Compared with monoculture, there was a significant difference in the temporal stability of intercropping wheat and faba beans under N1, N2, and N3 treatments. Under N1 and N2 treatments, there was a significant difference in structural stability between intercropped wheat and faba bean. The RII and A_WF of wheat were positively correlated with the temporal stability of aboveground biomass in the intercropping system, while the RII of faba bean was negatively correlated with the temporal stability of the intercropping system. In conclusion, intercropping has both competitive and synergistic effects on productivity stability, with the most obvious effect under the N2 treatment.

Key words: nitrate nitrogen, ammonium nitrogen, intercropping, competition, stability