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Effect of Inoculum Rate on Competitive Nodulation of Glycine max L. Merrill. II. Field Studies 1
Author(s) -
Weaver R. W.,
Frederick L. R.
Publication year - 1974
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1974.00021962006600020015x
Subject(s) - rhizobia , biology , bradyrhizobium japonicum , agronomy , inoculation , microbial inoculant , soil water , rhizobium , population , nitrogen fixation , rhizobiaceae , horticulture , symbiosis , bacteria , ecology , demography , sociology , genetics
To provide a scientific basis for predicting successful competitive nodulation of soybeans ( Glycine max L. Merr.) by Rhizobium japonicum , the quantitative relationship between soil and inoculum rhizobia, in nodule formation, was determined in the field. Soybean seeds were planted at a rate of 1 seed/2.5 cm of row and were inoculated with up to 3.3 ✕ 10 3 8 R. japonicum cells/2.5 cm of row. Field plots were grown on six soils in Iowa having a range of soil rhizobia populations of 1.2 ✕ 10 1 to 2.3 ✕ 10 5 /g of soil. Numbers of nodules on tap and lateral roots of soybeans grown on soils containing fewer than 12 rhizobia/g were increased when inoculation rates exceeded 3.3 ✕ 10 4 cells/seed. Neither numbers of nodules nor total nodule mass was increased by inoculation of soybeans grown on soils containing more than 1 ✕ 10 3 rhizobia/g. When an inoculation rate of 3.3 ✕ 10 6 rhizobia/seed was used on soybeans grown in soils with fewer than 12 rhizobia/g and in soils with approximately 1 ✕ 10 3 rhizobia/g, the inoculum strain produced, respectively, 65% and 35% of the nodules. From our results it may be predicted that if the inoculum rhizobia are to form 50% or more of the nodules an inoculum rate of at least 1,000 times the soil population (per g soil) must be used. Commercial inoculants in the United States probably are not supplying adequate numbers of rhizobia for successful competitive nodulation of soybeans grown on land previously cropped to soybeans.