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 mum) to prevent root contact, but allow N exchange, or no root barrier between the compartments to allow root intermingling. Root contact enhanced N-15 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 N-2 (%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 N-15 isotope dilution technique and by direct plant labeling via petiole injection of a N-15 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.