Soil Quality Assessment in Land Reclamation

The development and application of quantitative soil quality assessment (SQA) concepts involve
calibrating soil quality indicators (SQI), such as soil organic carbon (SOC), to soil management
goals such as yield or biomass productivity to create soil quality-scoring functions (SQF).
Currently, SQA is used primarily to evaluate agronomic land use, but the concept could easily be
applied to other land uses such as reclamation. To do so, the robustness and transferability of
predictive SQI and SQF must be demonstrated considering baseline variations between natural
and reclaimed soils. The indices must also be responsive to and meet the design criteria and
objectives of reclamation covers. Calibrating more complex, bi-directional and time sensitive
relationships between SQI and performance measures such as forest soil productivity will also
require defining SQF concepts needed to support a healthy forest stand, since that is often the
goal for reconstructing and revegetating disturbed soils. The objective of this research was to
develop quantitative, calibrated, justifiable and validated SQF within a SQA framework that
would be suitable for assessing, monitoring and managing land reclamation. An existing SQI
database and measures of ecosystem performance compiled over the last 30 years for Alberta oil
sand reclamation was used to develop SQF relationships that were validated for both site specific
and regional SQA scenarios. Accuracy and transferability of SQF were assessed based on their
ability to reproduce known or specific treatment effects from independent sites. Baseline SOC
variation was used as the main predictive indicator to identify functional management units and
define boundary conditions for SQF. Both analytical (GYPSY) and process-model (BIOMEBGC) options were used to calibrate SQF for effects of time and available water holding
capacity on forest productivity. Generally, SQF developed from natural soils were transferable
and justifiably rated the quality of peat-mineral mix covers in reconstructed soils. Although high spatial and temporal variation in SOC was observed at the regional scale, SOC values were
useful for defining and delineating functional management zones (p < 0.05) for further SQA
applications. Based on those soil management zones, critical SQF thresholds and metrics for
optimizing reclamation cover design were developed and evaluated based on their capability to
supply soil nutrients such as nitrogen (N) as a measure of their performance. Both the GYPSY
and BIOME-BGC models provided pre-validated outputs suitable for calibrating SQF. Finally, in
seven application scenarios completed within this study, integrated soil quality ratings generally
resulted in expected non-significant or significant (p < 0.05) treatment effects. The ratings
appeared to be more realistic than simply testing for changes in predictive soil quality indicators
in response to management goals for reclaimed soils. SQF also proved to be useful for
quantitatively defining equivalent capability functions for reclaimed soils, assessing quality of
both dry- and wet-land reclaimed soils and are suitable for monitoring the quality of reclamation
covers through all phases of restoration.