Transformations and movement of anhydrous ammonia-derived N in soils
Some studies have concluded that anhydrous ammonia is indistinguishable from other common nitrogen (N) fertilizers for corn (Zea mays L.) production, however, new soil and plant tissue tests give researchers more sensitive and precise tools for detecting situations where N may be deficient or sufficient. The existence of these new tools creates a need for a reexamination of the properties of anhydrous ammonia fertilizer. This dissertation reports results from several studies using N-15-labeled and nonlabeled anhydrous ammonia for corn production in Iowa. The objectives were (i) to evaluate the possibility that injection of anhydrous ammonia at sidedressing could result in reduced availability of N for growing corn plants, (ii) to evaluate the late-spring soil nitrate test and the end-of-season cornstalk test as tools for comparing broadcast N applied at different times of the year, (iii) evaluation of the effects of rate and timing of anhydrous ammonia on late-spring soil nitrate concentrations, end-of-season stalk nitrate concentrations, and corn yields, and (iv) comparisons of the effects of anhydrous ammonia and broadcast ammonium sulfate applied at selected rates and times;Results revealed no marked tendency for delayed availability of N for corn from sidedressed anhydrous ammonia. However, substantial quantities of N were incorporated into forms not readily available for plants. The late-spring soil nitrate test and the end-of-season cornstalk test were more effective tools for comparing the N-supplying power of broadcast fertilizers applied at different times than were measurements of corn grain yields alone. Yields of corn grain tended to show no effect of N rate or application time when anhydrous ammonia was applied at selected times of the year. However, the end-of-season cornstalk test revealed that broadcast ammonium sulfate had greater N-supplying power than banded anhydrous ammonia in wet years.