Spatial variability of soil nitrogen forms and the activity of N-cycle enzymes

Abstract

Knowledge about the spatio-temporal variability of soil chemical and biological properties is crucial in evaluating their structure-function relationship and their impact on ecosystem functions. A study was conducted in order to evaluate the spatial variability of nitrogen (N) forms and N-cycle enzymes of a Phaeozem located in the Northwestern Poland. Fifty soil samples were collected every 10 m from the area of 90 × 40 m that was selected from an 80 ha agricultural field after the harvest of winter wheat. The samples were analysed for total nitrogen (Ntot); mineral nitrogen (NO3--N, NH4+-N) and the activities of the N cycle enzymes - urease (UR), nitrate reductase (NR) and arginine deaminase (ADA). The coefficients of variation were low for Ntot content and UR activity, while a moderate variability was noted for mineral N and ADA activity and a high one was noted for NR activity. Most of the properties revealed a contribution of random variance (nugget effect) in total variability (sill), while only Ntot and ADA activity were determined by the structural variance. The effective ranges were from 11.9 m for NO3--N to more than 50.3 m for NH4+-N. Kriged maps showed that every property revealed a different distribution on the study area. The significant variability of the studied properties should be taken into account in soil management practices. Additionally, this knowledge would contribute to a better understanding of the nitrogen transformation in soil and functioning of the ecosystem.