Soil indicators set up to assess sustainable management in various agricultural and forest ecosystems
Author(s)
Papp, Ruxandra
Date Issued
June 16, 2016
Type
Doctoral Thesis
Abstract
The role of sustainable soil management is the promotion of soil quality by maintaining and enhancing soil ecosystem functions and services. Changes of soil quality over time in a short- medium and long-term represent a tool to evaluate if the management strategies can be considered sustainable. The overall aim of the thesis was to focus on the most sensitive soil quality indicators in order to assess sustainable management in both agricultural and forest ecosystems. Therefore, the main question posed was which soil indicators were more effective in discriminating between management practices. Four case studies were chosen considering, both agricultural and forest ecosystems, focusing on specific soil indicators for each ecosystem. Firstly, soil chemical and biological quality indicators were assessed separately along four case studies according to specific aims such as: (i) soil ecological impact of tillage and the use of subsidiary crops; (ii) organic versus agricultural management in a long-term experiment; (iii) impact of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) reforestations on soil chemical and biochemical properties; (iv) effect of past Beech tree (Fagus sylvatica L.) forest management on soil carbon sequestration and microbial diversity. Secondly, among the common soil chemical and biochemical properties assessed across the four case studies, the most sensitive indicators of soil management were selected for a final further statistical analysis. In the statistical model applied, soil pH and nitrogen pools (total and extractable) were chosen as independent variables. Soil pH is considered an intrinsic quality of soil that is less influenced by the soil management practices whereas the pools of nitrogen are usually more sensitive to management practices and indirectly could link the soil biochemical properties to the type of management applied. Furthermore, the dependent variables in the model were the soil specific enzyme activities (expressed per unit of carbon) and microbial quotient were tested in their sensitivity to discriminate between different management practices. Additionally, a fifth study case was considered in order to evaluate the soil microbial biomass functional diversity with respect to different soil categories and managements. In this case, the Shannon’s diversity index assessed with two types of methodologies (enzyme assays and Microresp®) was compared across a gradient of soil pH and organic carbon content.
The results obtained in the short term trials of agroecosystem showed that soil chemical properties (total organic carbon and total nitrogen) were not affected by the management. Conversely, the biological indicators such as microbial quotient and specific enzyme activities were significantly influenced by tillage and by the use of subsidiary crops. Furthermore, in the long-term trials of agricultural soil, organic systems and reduced tillage management practices positively influenced soil chemical properties in terms of soil total organic carbon, and enhanced the size and activity of soil microbial biomass. In forest ecosystems, soil chemical and biochemical properties changed with respect to the different tree stand ages and the type of forest management practices. In the case of different stands age of Douglas fir, the soil microbial size and activity was generally higher in the oldest stands, probably because they were affected by a nitrogen limitation. In the case of the Beech tree forest stands the heterogeneous forest structure given by previous forest management practices had significant effect on soil carbon sequestration and also on soil microbial functional and structural diversity.
The overall analysis conducted on the data of the common soil indicators across the four case studies showed that specific enzyme activities (expressed per unit of organic carbon) and microbial quotient can be considered sensitive indicators depending on soil pH in both agricultural and forest ecosystems. Conversely, the selected bioindicators became sensitive to soil management with respect to nitrogen availability only in the agroecosystems.
The soil microbial functional diversity calculated as Shannon’s index (H’) using the data from the community level physiological profiles proved to be more sensitive to land use and management practices than H’ calculated using enzyme activity patterns.
In this study the identification of the most sensitive indicators of soil management was limited to soil characteristics such as: pH, organic carbon and different nitrogen pools studied in relation to soil bioindicators. For future studies this approach could be extended to other soil characteristics such as texture considering them as independent variables in the statistical models.
Additional information
Dottorato di ricerca in Ecologia forestale
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