Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

R. M. Shibles


Corn (Zea mays L.) after soybean (Glycine max (L.) Merr.) consistently performs better than second-year corn irrespective of nitrogen fertilization. The reason for the yield advantage of this rotation is speculative. In previous work with the soybean-corn rotation, there has never been an evaluation of the potentially different effects of soybean varieties on following corn. A 2-year soybean-corn rotation was initiated in 1988 with the first year being planted to various soybean types, a corn plot, and an oat (Avena sativa L.) plot. This was followed by a single corn hybrid in the second year with varying N levels. Results are based on three repetitions of this cycle;Corn after corn yielded less than corn after other crops and was delayed in silking by 4 days. A further indication of the depressive effect of corn upon itself was that second-year corn plants were significantly shorter and thinner. Corn after oat was as good as corn after most soybean varieties. The responses of corn to oat and soybean, especially at zero N, imply that the N benefit of both was principally due to soil N mineralization. There was no net N benefit of soybean to corn. However, both soybean and oat benefitted corn even under high nitrogen fertilization. The reasons for this "rotation" effect are unknown;BSR 201 soybean benefitted corn more than the other soybean varieties. Corn after BSR 201 showed a positive rotational benefit even at the highest N level. Overall, BSR 201 soybean benefitted corn on average 676 kg/ha or 11 bu/A more than other soybean varieties. The reason for this is a subject for speculation.



Digital Repository @ Iowa State University,

Copyright Owner

Edgar S. Escuro



Proquest ID


File Format


File Size

100 pages