Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

M. A. Tabatabai


The activities of six enzymes involved in C, N, P, and S cycling were assayed in 10 surface soils each from Iowa and Costa Rica before and after waterlogging for times ranging from 0 to 6 days at 25°C. After waterlogging, Eh and pH were measured and the enzyme activities assayed at optimum pH values at 37°C. Results showed that Eh[subscript]7 values markedly affect enzyme activities in soils. The magnitude and trend of the effect varied among the enzymes ([beta]-glucosidase, amidase, urease, acid phosphatase, phosphodiesterase, and arylsulfatase) and soils studied. In general, the Eh[subscript]7 values decreased with time of waterlogging and so did the activities of the different enzymes, except phosphodiesterase activity which was increased;The effect of crop residue addition (alfalfa (Medicago sativa), corn (Zea mays L.), and soybean (Glycine max. L. Merr.)) on enzyme activities of two soils each from Iowa and Costa Rica was studied after preincubation at 25°C under waterlogged conditions for 3 days. The addition of crop residues resulted in a marked increase in the activity of the enzymes studied, except amidase and arylsulfatase;The effect of crop rotations on enzyme activities was studied in soil samples obtained from three research sites in Iowa: at Kanawha, Sutherland, and Nashua. The sites have been under crop rotation experiments since 1954, 1957, and 1978, respectively. In general, the rotations corn-oats-meadow-meadow, corn-corn-oats-meadow, and corn-soybean-corn-soybean resulted in greater soil enzyme activities than those of continuous corn;The effect of crop residue addition on enzyme activities was studied in two soils each from Iowa and Costa Rica treated with crop residues (alfalfa, corn, and soybean) and incubated at 25°C under aerobic conditions for times ranging from 0 to 21 days. The results showed that these organic materials increased enzyme activities of soils, and that the changes in the level of activity was dependent on the enzyme, type of crop residue, chemical and physical properties of soils, and time of incubation;Waterlogging of soils, crop rotations, and soil management practices markedly affected the reaction rates of enzymes and, possibly, nutrient cycling.



Digital Repository @ Iowa State University,

Copyright Owner

Jorge Arturo Briceño-Salazar



Proquest ID


File Format


File Size

171 pages