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Intercropped Oat and Fababean in Alaska: Dry Matter Production, Dinitrogen Fixation, Nitrogen Transfer, and Nitrogen Fertilizer Response

USDA-ARS, Northern Plains Soil & Water Res. Ctr., P.O. Box 1109, Sidney, MT 59270
USDA-ARS, 309 O'Neill Bldg., Univ. of Alaska Fairbanks, Fairbanks, P.O. Box 757200, Fairbanks, AK 99775-720

^* Corresponding author (Email: !a031csidney@attmail.com).

There are conflicting reports on the amount of N transferred from legumes to intercropped nonlegumes and on the need for N fertilizer to obtain high total dry matter yields on soil with low N availability. This study evaluates (i) the ability of fababean (Vicia faba L.) to meet its N requirements from biological N₂ fixation: (ii) the amount of N transferred to intercropped oat (Avena sativa L.); and (iii) N fertilizer management to maximize dry matter production and N₂ fixation in a cold soil. A randomized complete block experimental design with four replications was used with two rows of fababean alternating with two rows 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) oat –N, fababean –N,+I; (iv) oat –N, fababean +N,–I; and (v) oat –N, fababean –N, + I. A second study compared uptake of ¹⁵N-depleted fertilizer by oat and fababean, where the fertilizer was broadcast over the plot or band-applied between rows of oat and fababean planted in alternate rows. Less than 1% of the uninoculated fababean plants nodulated in either experiment; thus, they were a good check for estimating N₂ fixation using the difference method. Nitrogen fertilizer increased dry matter production of fababean in some years, but did not increase N uptake. 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 the oat and not the fababean in 3 of the 4 yr. The amount of N₂ fixed by fababean averaged 50 kg N ha^–1. Fababean plants obtained >50% of their N from broadcast urea, but < 10% when urea was banded between oat and fababean rows. Configuring a commercial drill to band fertilizer between pairs of oat rows alternating with fababean is a practical way to maximize both N₂ fixation and total dry matter production.

Received for publication March 31, 1994.