Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

M. Ali Tabatabai


Studies were undertaken to investigate the long-term effects of lime application and tillage systems (no-till, ridge-till, and chisel plow) on soil microbial biomass C (Cmic) and N (Nmic) and the activities of glycosidases (alpha- and beta-glucosidases, alpha- and beta-galactosidases and beta-glucosaminidase); phosphatases (acid and alkaline phosphatases and phosphodiesterase); amidohydrolases (L-asparaginase, L-glutaminase, amidase, urease, and L-aspartase); and arylamidase at their optimal pH values. With the exception of acid phosphatase, which was significantly but negatively correlated, all other enzyme activities were significantly and positively correlated with soil pH values at four sites in Iowa. Delta activity/Delta pH values showed that among the enzymes studied beta-glucosidase, L-glutaminase, and acid phosphatase are the most sensitive to pH changes and could be used as tools for monitoring ecosystems health and function.;The effect of crop rotations and N fertilization on beta-glucosaminidase activity and its relationship to N mineralization were studied in soils of two long-term field experiments in Iowa. The activity of beta-glucosaminidase was significantly affected by crop rotations and N fertilization, and was significantly correlated with Corg and Norg, C mic, and Nmic in soils, and with cumulative N mineralized during 24 weeks of incubation at 30°C.;Studies to evaluate the effects of 23 trace elements on the activity of beta-glucosaminidase in three Iowa surface soils showed that at 5 mmol kg-1 soil, the activity of this enzyme was inhibited by 18, and activated by 5, of the trace elements tested, with Ag(I) and Hg(II) being the most effective inhibitors. Also, the activity of this enzyme was significantly affected by tillage systems (no-till, chisel plow, and moldboard plow) and four residue placements (bare, normal, mulch, and double mulch).;Other studies showed that the amounts of N mineralized in 56 surface soils, obtained from six states in the North Central region of the United States, by two biological and three chemical methods were significantly correlated with beta-glucosaminidase activity, and with organic C and total N. The amounts of N mineralized during 14 days of incubation of field-moist soils under waterlogged conditions at 30°C were the most significantly correlated with beta-glucosaminidase activity (r = 0.86***).



Digital Repository @ Iowa State University,

Copyright Owner

Mine Ekenler



Proquest ID


File Format


File Size

280 pages