INTERCROPPED OAT AND FABABEAN IN ALASKA - DRY-MATTER PRODUCTION, DINITROGEN FIXATION, NITROGEN TRANSFER, AND NITROGEN-FERTILIZER RESPONSE

There are conflicting reports on the amount of N transferred from legu mes to intercropped nonlegumes and on the need for N fertilizer to obt ain high total dry matter yields on soil with low N availability. This study evaluates (i) the ability of fababean (Vicia faba L.) to meet i ts M requirements from biological Ni fixation: (ii) the amount of N tr ansferred to intercropped oat (Avena sativa L.); and (iii) N fertilize r management to maximize dry matter production and N-2 fixation in a c old soil. A randomized complete block experimental design with four re plications was used with two rows of fababean alternating with two row s of oat. Urea was applied in bands between fababean or oat rows at 90 kg N ha(-1) to get the following treatments: (i) oat with added N (+N ), fababean +N, inoculated with Rhizobium leguminosarum by. viceae (+I ); (ii) oat +N, fababean without added N, inoculated (-N,+I); (iii) oa t -N, fababean -N,+I; (iv) oat -N, fababean +N,-I; and (v) oat -N, fah abean -N,+I. A second study compared uptake of N-15-depleted fertilize r by oat and fababean, where the fertilizer was broadcast over the plo t or band-applied between row of oat and fababean planted in alternate rows. Less than 1% of the uninoculated fababean plants nodulated in e ither experiment; thus, they were a good check for estimating N-2 fixa tion using the difference method. Nitrogen fertilizer increased dry ma tter production of fababean in some years, but did not increase N upta ke. There was little evidence of N transfer from fababean to oat. Oat depended on N fertilizer for maximum dry matter production 3 of the 4 yr. Maximum total dry matter production was achieved by fertilizing th e oat and not the fababean in 3 of the 4 yr. The amount of N-2 fixed b y fababean averaged 50 kg N ha(-1). Fababean plants obtained >50% of t heir N from broadcast urea, but <10% when urea was banded between oat and fababean rows. Configuring a commercial drill to band fertilizer b etween pairs of oat rows alternating with fababean is a practical way to maximize both N-2 fixation and total dry matter production.