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Dinitrogen Fixation Measurements in Alfalfa‐Ryegrass Swards Using Nitrogen‐15 and Influence of the Reference Crop
Author(s) -
Hardarson G.,
Zapata F.,
Danso S. K. A.
Publication year - 1988
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1988.0011183x002800010022x
Subject(s) - lolium perenne , agronomy , legume , biology , nitrogen fixation , seeding , medicago sativa , crop , nitrogen , field experiment , poaceae , zoology , chemistry , genetics , organic chemistry , bacteria
The accuracy of 15 N estimates of N 2 fixation may be influenced by the choice of the reference crop, especially in mixed legume‐grass swards, where transfer of fixed N 2 from the legume to the reference crop may occur. To investigate this, a 2‐yr field experiment was conducted in a Typic Eutrocrepts soil in Austria to measure N 2 fixed in alfalfa ( Medicago sativa L.) grown alone or in two seeding ratios with ryegrass ( Lolium perenne L.), using pure or mixed sward ryegrass as the reference crop. Alfalfa, on the average, derived over 80% of its N from fixation over the 2‐yr period, equivalent to about 415 kg N/ha. Compared to N 2 fixation in pure alfalfa sward, the % N derived from atmospheric N 2 (% Ndfa) in alfalfa increased significantly in the mixed sward and even more by increasing the seeding ratio of ryegrass in the mixture. Except for the first harvest, the atom % 15 N excess in mixed ryegrass was slightly lower than in the pure grass. These differences in 15 SN enrichment were insignificant, suggesting that the possible release of N from alfalfa and subsequent uptake by ryegrass may have been small. The highest proportion of ryegrass N that could have been derived from the legume was estimated to be 16% in the second harvest, equivalent to only 4 kg N/ ha and <10 kg N/ha over the 2 yr. These differences in 15 SN enrichments of pure and mixed ryegrass reference plants did not significantly affect the estimates of % Ndfa in alfalfa.