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Mobilization of 15 N from Soybean Leaves as Influenced by Rhizobial Strains 1
Author(s) -
Morris Dolen R.,
Weaver W.
Publication year - 1983
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/cropsci1983.0011183x002300060021x
Subject(s) - point of delivery , rhizobia , biology , rhizobium , nitrogen fixation , horticulture , inoculation , petiole (insect anatomy) , strain (injury) , yield (engineering) , botany , agronomy , bacteria , hymenoptera , genetics , anatomy , materials science , metallurgy
Nitrogen nutrition of soybeans [ Glycine max (L.) Merr.] during pod development is important in determining seed yield. Soybeans utilize leaf N to meet the N needs of developing fruit which may reduce yield potential. A field experiment was undertaken using 15 N to test the hypothesis that high N 2 ‐fixing rhizobia would delay mobilization of N from leaves to developing pods. Three strains of Rhizobium japonicum , USDA strains 110, 31, and an ineffective mutant of strain 8‐0, varying in N 2 ‐fixation effectiveness were used as inoculum to determine their influence on the utilization and translocation of N during pod fill. Foliarly applied 15 N urea was sprayed onto leaves five times prior to pod formation to label vegetative N. Total application of N was approximately 3 kg/ha. During the first 17 days of pod development approximately 25% of the incorporated 15 N was mobilized to the pods regardless of the rhizobial strain. During the final stages of pod development, mobilization of labelled N continued at nearly a linear rate for all rhizobial treatments. for USDA strain 110, there was an insignificant net loss in leaf and petiole N during the first 17 days of pod development which indicated there was an exchange between N 2 recently fixed and N previously incorporated into leaves. The rate of N 2 ‐fixation by both effective strains of rhizobia increased during pod development. Even though strain 110 fixed more total N than strain 31 the final seed yield for both treatments was similar due to differential partitioning of N. Future research is needed to elucidate the partitioning of N 2 fixed during pod development and to determine why the better N status of plants inoculated by strain 110 did not result in increased yields.