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Title: LONG-TERM STUDY OF CROP ROTATION EFFECTS ON SOYBEAN SEED COMPOSITION

Author
item BENNETT, JOHN - AGRONOMY-UNIV OF MISSOURI
item Krishnan, Hari

Submitted to: Korean Journal of Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2005
Publication Date: 3/1/2005
Citation: Bennett, J.O., Krishnan, H.B. 2005. Long-term study of crop rotation effects on soybean seed composition. Korean Journal of Crop Science. 50:32-38.

Interpretive Summary: Crop rotation is an age-old agricultural practice which maintains productivity with limited resources. Technological advances in agricultural production have led to monocultures of grain and minimized the use of crop rotation. However, in recent years, the high cost of production coupled with diminishing economic returns and environmental concerns have stimulated interest in earlier methods of production. Research has shown that crop rotation contributes to the enhancement of soil and environmental quality. In our study, we found that the quantity and quality of protein and oil produced by the soybean can be influenced by specific crop rotation system. Results from our study indicate that judicious selection of crop rotation system could allow the farmer to produce soybeans which yield high quality protein and oil, thereby enhancing profitability.

Technical Abstract: A long-term study initiated in 1989 at Sanborn Field, Columbia, Missouri, was designed to evaluate the affect of environmental factors, nitrogen application, and crop rotation on soybean (Glycine max [L.] Merr.) seed composition. Soybeans were grown as part of a four-year rotation which included corn (Zea maize L), wheat (Triticum aestivum L), and red clover (Trifolium pratense L). Results from soil tests made prior to initiation of the study and subsequently every five years, were used to calculate application rates of nitrogen, phosphorus, and potassium necessary for target yield of pursuant crops. In the experimental design, nitrogen was applied to one-half of the plot on which non-leguminous crops, corn or wheat, were grown. Analysis of soybean seed by near infrared reflectance spectroscopy collected over an 11-year period revealed a linear increase in protein and decrease in oil content. Application of nitrogen fertilizer to the non-leguminous crops did not have an apparent affect on total protein or oil content of subsequent soybean crop. Analysis of soybean seed proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis in conjunction with computer-assisted densitometry revealed subtle changes in the accumulation of seed proteins. Immunoblot analysis using antibodies raised against the beta-subunit of beta-conglycinin showed a gradual increase in the accumulation of the 7S components during successive years of the experiment. A linear increase in temperature and decrease in rainfall was observed from the onset of data collection. Higher temperatures during the growing season have been linked to increased protein and diminished oil content of soybean, thus changes observed in this study are possibly related to climatic conditions. However, crop rotation and subsequent changes in soil ecology may contribute to these observed changes in the seed composition.