Agronomy Journal Journal of Natural Resources and Life Sciences Education
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Published online 1 May 1981
Published in Agron J 73:505-508 (1981)
© 1981 American Society of Agronomy
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Effect of Rhizobium japonicum Inoculant Rates on Soybean Nodulation in a Tropical Soil1

R. S. Smith, M. A. Ellis and R. E. Smith2

Soybean [Glycine max (L.) Merr.] research and production is expanding in tropical areas. Successful soybean nodulation in a soil free of Rhizobium japonicum is dependent totally upon viable rhizobia from the inoculant. This study examined soybean nodulation as influenced by the rate of applied R. japonicum in a tropical soil without indigenous R. japonicum.

Rates of R. japonicum were evaluated with soybeans grown in a field experiment on a Puerto Rican Coto clay (Typic Haplorthox, clayey, kaolinitic, isohyperthermic) lacking indigenous R. japonicum. Eight rates of liquid inoculation were added to the seed furrow at planting and supplied number of R. japonicum from log 2.59 cells/cm row with 10 fold increases through log 9.59 cells/cm row. R. japonicum rates of log 239 and 3.59 cells/cm row were not successful in establishing nodulation. Nodule numbers increased with increasing rates of applied rhizobia from log 4.59 up to the highest rate of log 9.59 viable cells/cm. Regression analyses indicated linear relationships between the rate of inoculation with rhizobia and the number of tap root nodules, total number of nodules, and nodule weight/plant. An inverse relationship was observed between weight/nodule and total number of nodules. Inoculation levels above log 5.0 rhizobia/on were necessary to establish effective nodulation in a R. japonicum free tropical soil.

Key Words: Nodulation • Inoculating rates • Glycine max (L.) Merr.

1 Contribution from the Dep. of Agronomy, Univ. of Illinois. Urbana, IL 61801, and Dep. of Crop Protection and Dep. of Agronomy, Univ. of Puerto Rico, Mayaguez, P.R. 00708. Research supported by the U.S. Agency for International Development under Contract No. AID/tac-1294. The views and interpretations are those of the authors and should not be attributed to the Agency for International Development or to any individual acting in their behalf.

2 Assistant professor of agronomy, Univ. of Illinois (currently research director, Nitragin Co., Inc., Milwaukee, Wis.), assistant professor of crop protection, Univ. of Puerto Rico (currently assistant professor, Ohio Agric. Res. and Devel. Ctr., Wooster, and Ohio State Univ., Columbus, Ohio), and associate professor of agronomy, Univ. of Puerto Rico (currently Great Lakes Chemical Corporation, West Lafayette, Ind.), respectively.

Received for publication August 1, 1980.




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Environmental Quality		 The Plant Genome
Copyright © 1981 by the American Society of Agronomy.