Effect of root contact on interspecific competition and N transfer between wheat and fababean using direct and indirect 15N techniques

Pot experiments were carried out to investigate the complementary N use between intercropped fababean (Vicia faba L. cv. Linxia Dacandou) and wheat (Triticum aestivum L cv. 8354). These pots were separated into two compartments, either by a solid barrier to prevent root contact and N movement, by a nylon mesh (30 μm) to prevent root contact, but allow N exchange, or no root barrier between the compartments to allow root intermingling. Root contact enhanced 15N acquisition of wheat but decreased that of fababean. Nitrogen derived from fertilizer (Ndff) by wheat was 73, 91 and 130 mg pot−1 in the treatment with solid barrier, with mesh barrier and without barrier, respectively. For fababean, these values were 38, 25 and 8 mg pot−1, respectively. Accordingly, increased competition from wheat roots resulted in a decrease in soil and fertilizer N uptake by fababean, and correspondingly, higher percentage of N derived from atmosphere N2 (%Ndfa). The %Ndfa of fababean was 58%, 80%, and 91% in the treatment with solid barrier, with mesh barrier and without barrier, respectively. Nitrogen transfer from fababean to wheat was estimated by the indirect 15N isotope dilution technique and by direct plant labeling via petiole injection of a 15N solution. With the indirect method, N transferred from fababean to the associated wheat was 2 mg with a mesh barrier and 6 mg without barrier. Using direct labeling method, N transferred from fababean to companion wheat was 7 mg, equal to 15% of total N in wheat.