MICROBIAL AND SOIL PARAMETERS IN RELATION TO N MINERALIZATION IN SOILS OF DIVERSE GENESIS UNDER DIFFERING MANAGEMENT-SYSTEMS

Oregon soils from various management and genetic histories were used i n a greenhouse study to determine the relationships between soil chemi cal and biological parameters and the uptake of soil mineralized nitro gen (N) by ryegrass (Lolium perenne L.). The soils were tested for asp araginase. amidase, urease, beta-glucosidase, and dipeptidase activiti es and fluorescein diacelate hydrolysis. Microbial biomass carbon (C) and N as well as metabolic diversity using Biolog GN plates were measu red, as were total soil N and C, pH, and absorbance of soil extracts a t 270 nm and 210 nm. Potentially mineralizable N (N-0) and the mineral ization rate constant (k) were calculated using a first order nonlinea r regression model and these coefficients were used to calculate the i nitial potential rate of N mineralization (N(0)k). Except for Biolog G N plates, the other parameters were highly correlated to mineralized N uptake and each other. A model using total soil N and beta-glucosidas e as parameters provided the best predictor of mineralized N uptake by rgiegrass (R-2=0.83). Chemical and biological parameters of soils wit h the same history of formation but under different management systems differed significantly from each other in most cases. The calculated values of the initial potential rate of mineralization in some cases r evealed management differences within the same soil types. The results showed that management of soils is readily reflected in certain soil chemical and biological indicators and that some biological tests may be useful in predicting N mineralization in soils.