Degree Type


Date of Award


Degree Name

Doctor of Philosophy




The study was undertaken to investigate the potential of relay intercropping soybean into oat in Iowa. The purpose of this study was to determine the optimum soybean planting date, row spacing, cultivar and oat harvesting date in an oat-soybean relay intercropping system. Two experiments were carried out in 1983, 1984, and 1985. Experiment I included three cropping system row spacings and three soybean planting dates. Experiment II included three soybean cultivars, three cropping system row spacings, and three oat harvesting dates;Relay intercropping soybean into oat significantly reduced grain yields of oat and soybean. The oat plant characters measured were not significantly affected by cropping systems. On the contrary, relay intercropping decreased the performance of all soybean plant characters except for number of branches per plant. Alteration of cropping system row spacing did not affect any soybean plant character, but significantly affected oat grain yield and test weight. The greatest oat grain yield and test weight were obtained when soybean was relay interplanted in 25-cm cropping system row spacing;Neither soybean planting date nor soybean cultivar had a significant effect on oat plant characters. The opposite was true for soybean plant characters. The earlier the soybean planting date, the greater the grain yield and the larger the seed size of soybean. Soybean cultivar significantly affected soybean plant characters measured, but not the grain yield and soybean plant height at oat harvest. Pella soybean had greater seed weight and plant height than Hobbit and Asgrow 3127 soybean. Regardless of soybean cultivar, the greatest soybean grain yield, seed weight, and plant height were achieved when soybean was relay interplanted in 51-cm row spacing;Oat harvest at physiological maturity resulted in greater oat grain yield and other plant characters as compared to harvest at harvest maturity. For soybean, the earlier the oat was harvested, the greater the soybean yield and seed weight;Land Equivalent Ratio (LER) values revealed that LER was not affected by either soybean cultivar, soybean row spacing, or oat harvesting date. The LER value of more than unity obtained from this research indicates that relay intercropping of soybean into oat has potential for Iowa.



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Nantawan Sarobol



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172 pages