Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Alfred M. Blackmer


Alfalfa (Medicago sativa L.) contributes substantial amounts of N to corn (Zea mays L.) crops that follow, but there is uncertainty concerning the amounts contributed. This causes uncertainty concerning amounts of fertilizer that should be applied to the corn. Such uncertainty is a matter of concern because rates of N fertilization influence both the profitability and the environmental costs of corn production;Studies were conducted to determine optimal rates of N fertilization for first- and second-year corn after alfalfa. Yield response trials involving seven rates of N in first-year corn were conducted at 29 locations during four years. Yield response trials involving ten rates of N in second-year corn were conducted at 24 locations during four years. The late-spring soil test and the end-of-season cornstalk test were evaluated as tools that enable development of recommendations that do not use the concept of fertilizer-N equivalence;Fertilizer significantly increased yields at 6 of the 29 trials in first-year corn. The most profitable rate of N fertilization across the 29 trials was mainly determined by cost of fertilization and value of grain, but ranged from 0 to 25 lbs N/acre at prices prevailing in the Corn Belt. These rates are lower than most producers apply, and use of the soil and tissue tests should help producers avoid unnecessary fertilization;Fertilizer significantly increased yields at 8 of the 24 trials in second-year corn. The profitability of fertilization was largely determined by ability to identify responsive trials, and the soil test was shown to have this ability. Profits would have been maximized by applying 75 lbs N/acre to trials testing less than 8 ppm by the soil test and no fertilizer to trials testing greater than 8 ppm;Overall the results show that use of the late-spring soil test and the end-of-season cornstalk test should help producers increase their profits by reducing costs of fertilization for corn after alfalfa. Additional benefits would include substantial reductions in the environmental costs associated with the use of N fertilizer.



Digital Repository @ Iowa State University,

Copyright Owner

Thomas Francis Morris



Proquest ID


File Format


File Size

115 pages