Soil Quality Evaluation Program
The report to follow identifies the requirement and provides a framework for soil quality evaluation. It summarizes the development of improved capabilities for assessing soil quality and for analyzing the impact of soil degradation on soil quality and crop productivity. It also provides some insights into the status of soil quality in Canada that have been forthcoming as part of the system developments. An overview of these various developments is presented below.A framework for soil quality evaluation has been developed which considers soil quality as the capacity of the soil to produce crops in a sustainable manner without impacting negatively on the environment. This recognizes the important role played by soils in providing a media for plant growth, regulating and partitioning the flow of water and gases in the environment and in providing an effective buffer for the environment. The framework proposes that soil quality evaluation for environmental reporting should involve large-area assessment of critical attributes or of processes known to modify soil quality and that these assessments should rely on predicted change to these attributes or processes based on the application of simulation models to standard databases of soils, land use, climate and topography. In addition, it recognizes the need for an independent capability to validate and calibrate this predictive capability.
Specific studies were established to understand more completely and, using computer models, to simulate various soil degradation processes as a basis for soil quality evaluation. This has resulted in the development and testing of a series of capabilities that provide or have the potential to provide independent indicators of soil degradation risk as well as composite indicators of soil quality. These studies include:
A prototype of an operational geographic information system was developed in Manitoba and southern Ontario to assess the current status and trends in soil quality. This system uses data from the Soil Landscapes of Canada map to assess inherent soil quality for crop production. Susceptibility to change to this inherent soil quality is then predicted by applying knowledge of the soil-modifying processes in conjunction with land and management data. Although the current prototype system is limited, further development will provide a system that should meet the requirements to periodically assess soil quality to support the State of Environment (SOE) reporting activity in Canada.As a basis for the analysis of land use and management, files linking Statistics Canada Census of Agriculture data to land resource databases have been completed for the Prairies and Ontario. These files provide access to more than 100 farm characterization variables that are spatially stratified by soil and landscape criteria. A generic spatial decision support system has been developed to facilitate integrated analysis of soils and census-derived land use information for these broad-scale assessments. The high potential of remote sensing for assessments of soil quality at regional and local levels was demonstrated using Landsat (TM) imagery.
A network of experimental sites was established to monitor soil quality at 23 benchmark sites representing typical farming systems and dominant soils and landscapes within the major agricultural regions of Canada. Baseline data collection has been completed and the preparation of databases will be completed by 1995. On-site monitoring of climate, crop yield, land use and management practices will enable the assessment of soil quality change by periodic resampling of the sites. The sites also will be used to validate computer models which relate soil degradation to crop production and, as mentioned above, to serve as a basis for validating predicted change to soil quality.A capability to monitor soil quality has been developed and tested. An assessment of the main degradation factors at some of the more susceptible locations reveals that soil degradation continues to be a serious threat to soil and environmental quality and crop productivity. Over the next few years, efforts will be concentrated on developing a fully national assessment of the current situation and trends over time. This will provide a scientifically-sound, quantitative measure of soil quality, and its economic impact in terms of productivity, as a function of time. This will provide a firm basis for the development of future land use and conservation policies.
HIGHLIGHTS OF SCIENTIFIC PROGRESS FROM 1990 TO 1993A conceptual framework for soil quality assessment has been completed and a draft document prepared that identifies appropriate methods for measuring soil quality attributes in the field and the laboratory.
Operational geographic information systems have been developed using two commercial GISs to integrate information for the assessment of soil quality at regional and national scales. These systems have been demonstrated for MB (Manitoba) and ON (Ontario). Cross-scale comparisons have been conducted to determine the degree of generalization involved in the national-level assessments. The appropriateness of various ground- and satellite-based sources of land use information was determined for each scale of assessment and the applicability of digital elevation data for upgrading topographic information provided on detailed soil maps was assessed. Procedures have been developed to assess the status of soil quality from data collected at some point in the past and to estimate the kind and direction of ensuing change by specific processes.Files linking Census of Agriculture and Soil Landscapes of Canada (SLC) are complete for MB, SK (Saskatchewan)and AB (Alberta). Efforts to link Enumeration Areas to SLCs for ON and NS are continuing. Census Consolidated Subdivision data has been purchased for ON, NS (Nova Scotia), MB, SK and AB in order that dependent projects can proceed with some analyses. Farm type and characterization data has been extracted from the Census on the basis of Agricultural Resource Areas for MB, SK and AB. An image analysis capability has been established at the CLBRR to augment land use data from the Census with that from remote sensing. The development of a database management system, ELLY (Encyclopedia for Landscape and Land-Indexed Inquiry), custom designed for the SLC and associated Census data has been completed and demonstrated.
A network of 22 Soil Quality Benchmark sites has been established. Baseline characterization and documentation has been completed for two sites and is nearly complete for nine additional sites. One site has been re-sampled to determine change to parameters affecting soil quality in the four years since baseline levels were determined.Progress in the development of protocols and data collection procedures for testing and validation of the Wind Erosion Research Model (WERM), being developed by USDA/ARS, has been impressive but development of the model has only reached the prototype stage, hence, original plans to have an operational capability to simulate wind erosion on an event basis by the end of the NSCP period will not be met. A model validation site was established at Lethbridge and erosion losses were monitored over 4-6 week periods in the spring and late fall-early winter of 1991 and 1992. Sixteen erosion events representing a total loss of 144 Mg ha-1 or an average depth of 14.4 mm of topsoil were reported over the 3 ha site. The results will be instrumental in ensuring the WERM model will appropriately accommodate wind erosion conditions in western Canada and the Chinook Belt of Alberta, in particular. The impact of erosion on crop productivity also was measured at this site and the relationship was represented by a linear equation.
Studies at Lethbridge, aimed to validate the Tillage and Soil submodels focused on winter breakdown of aggregates under various tillage treatments and the impact of winter weather conditions on aggregate size distribution and surface roughness. Field investigations have been completed in MB to compare the impact of various tillage practices and crop rotations on crop residues and aggregate size and strength as well as to determine straw/grain relationships for several crops. A simplified method to determine surface roughness also was evaluated. Soil credibility and residues were measured on chemical and conventional fallow treatments on several soils near Melfort, SK, and results compared to those from USDA that were used for developing the Soils and Decomposition submodels. Documentation of results for these various studies is in progress. Wind erosion monitoring sites were established in AB, SK, and MB to quantify erosion events under typical management practices. Erosion was not extensive in the wet spring of 1991 but single event losses as high as 7 Mg ha-1 and total losses of 10 Mg ha-1 for five events were recorded for one AB site in 1992. An image analysis technique for estimating crop residues was evaluated as a potential component of a residue management model.A water erosion monitoring and prediction study entailed conducting baseline monitoring of soil erosion rates on agricultural landscapes across Canada. Cs-137 soil samples were analyzed from field-scale plots in BC (British Columbia), MB, ON, QU (Quebec), and NB (New Brunswick). Watershed-scale plots were sampled for Cs-137 analysis in SK and PEI (Prince Edward Island). Soil re-distribution at 2 QU sites averaged 24.3 and 12.9 t/ha/yr. The average soil movement per year of tillage was almost the same at each site. The most eroded landscapes positions at the 2 sites had lost 97 and 64 t/ha/yr. Soil movement from continuous potato production in NB averaged 53 t/ha/yr with a maximum value of 190 t/ha/yr over the last 30 years. Potato yield data showed a strong relationship with soil movement; about 0.15% loss of yield was associated with each 1 t/ha/yr soil loss.
Validation of the Revised Universal Soil Loss Equation (RUSLE) and WEPP model developed as part of the Water Erosion Prediction Project of USDA/ARS is ongoing since the models have just become available in their final forms. Preliminary versions of the WEPP model have been evaluated on microplot-scale data in ON, where sensitivity analysis of important input parameters has been conducted. The final version of the WEPP model will be tested with erosion plot data from across Canada. Then, it will be used in conjunction with the Cs-137 data to compare actual and predicted soil redistribution on a landscape. Winter erosion data from BC, ON, and MB will be used to evaluate the winter runoff and soil loss routines of the model. Recently-collected soil erosion data in BC and NB will be used to conduct a validation of RUSLE under Canadian climatic conditions. Climatic data on freeze-thaw cycles, rainfall on frozen ground, and snowmelt data was combined with winter soil loss data to better understand and predict winter soil erosion losses. Climatic data files are being compiled for 32 locations across Canada for use in erosion prediction equations.The soil landscape maps for Canada were used as the basis for establishing water erosion risk maps. The risk of water erosion was estimated using the USLE for each polygon on the soil landscape map. A handbook for the estimation of water erosion in Canada is being compiled to provide soil conservation planners with current information for USLE or RUSLE soil loss predictions. It is intended that the information in the handbook will improve the reliability of erosion predictions made with these existing methods.
The CENTURY organic matter simulation model was tested for Canadian climate, soils and crop rotations using data from long-term rotation studies in western Canada and erosion, tillage, and fertility plots in ON and QU. The model accurately simulated changes in soil organic carbon and nitrogen in the long- (more than 80 yr) and short- (less than 5 yr) term. Simulations under eroding conditions indicated that erosion was the primary process controlling organic matter levels in soil. In addition to the modelling, soils under different management regimes were sampled at 22 sites in eastern Canada to assess the effects of cultivation on the quantity and quality of soil organic matter. The mass of carbon in cultivated soils was about 35% less and the mass of nitrogen 20% less than in forested soils. Several cultivated soils had greater levels of nitrogen than corresponding forested soils. Work is continuing to develop a soil quality index for soil organic matter.Seven sites have been instrumented and characterized for monitoring and modelling the long-term status of soil salinity for representative agricultural landscapes in the Canadian Prairies. Comprehensive data sets have been assembled for each of these sites. Preliminary evaluation suggests that the extent of salinity is not increasing at any of the sites, although there is some fluctuation in concentration of salts within the sites. Contaminant transport models (SEEP/W and CTRAN/W) have been used to simulate salinization processes at each site so as to determine the relative importance of the various factors controlling salinity. Preliminary output has identified the water flux at the soil surface as the major controlling factor in the dynamics of soil salinization. It also has shown that most of the salts in the saline fringe area of a glacial morainal slough are locally derived and are the result of shallow, local redistribution over short distances through geologic time.
Procedures involving field and laboratory measurements were developed and later modified for the measurement of the Non-limiting Water Range (NLWR) of soils. The field procedure included infiltration and redistribution of added water to allow measurement of the wet end of the soil-water desorption curve with a single measurement of water content and soil water potential. In the laboratory, the penetrometer resistance of soil cores dried to different soil-water potentials was used to interpret both the aeration limits and the strength limitations for root growth. Soils at nine locations across Canada having a variety of cultivation histories were studied. The major findings include: an improved procedure for desorption of soil cores and a new soil probe design for the combined and simultaneous measurement of water content and water potential in the soil; the increasing soil strength which appears to be occurring under cultivation is limiting the availability of soil water more than has been previously recognized; about 20% of the soil horizons studied are showing inadequate aeration porosity, leading to possible restrictive root development; some of the intensively-cultivated soils showed a reluctance to wet, which gave non-uniform distribution of the infiltrated water and limited water retention; and the attempted application of the NLWR concept provided indications of some of the possible causes of soil physical degradation.In another approach to evaluate change to soil structure, stress-strain functions were determined for 12 of the main soil associations found in the Regional Municipality (RM)of Haldimand-Norfolk, ON. These data were used in conjunction with estimated soil moisture profiles from the soil water retention model (SWATRE) to derive probability distributions for total soil porosity changes during critical periods of the corn growing season. Comparison of stress-strain relationships (remoulded vs structured) resulted in a segregation of the Haldimand-Norfolk soils into 3 groups based on the relative positions of these stress-strain functions under saturated conditions (i.e. degree of over consolidation). Crop cover information was overlain with generalized soil mapping to identify the soil landscapes that are most susceptible to traffic-induced soil compaction from row cropping. A key finding is that earlier model forms for soil compression do not perform well on structurally intact subsoils. Secondly, the compressive behaviour of structured soils in this municipality can be predicted reasonably well from consolidation behaviour of the remoulded (slurried) soils and hence from their consistency limits. This enables the development of a soil survey interpretive procedure whereby a user can interpret the magnitude of below-ground limitations to crop productivity arising from high soil strength from fundamental and widely accessible data on soil physical properties.
A study of the modelling and monitoring of agrochemical migration in soil showed that approaches being used were highly variable and generally of local scale or specific intent. An assessment of modelling practices led to the choice of the Leaching Estimation And CHemistry Model (LEACHM) for predicting the fate and transport of chemicals in the root zone. The model was modified to allow its use in situations where the water table comes into the zone of analysis and the functions used to represent the soil water properties were changed to use those proposed by Van Genuchten. The expansion from point data, as resulting from the LEACHM model, to regions was achieved using geostatistical analysis, followed by kriging to estimate values of parameters for grid points. A GIS was used to identify factors controlling the root zone migration of chemicals in the Grand River, ON watershed. Linear correlation coefficients indicate that the loadings reaching the groundwater table results from a complex interaction of many soil and climate factors. The atrazine loadings were predicted to be very low where soils are fine-textured and high on alluvial sands. Thus, this approach is useful in identifying the regions of higher risk from agrochemical migration.An analysis of FP&I (Food Production and Inspection) well water data showed that nitrate levels in some of the sampled wells were high but the ancillary data were not useful in identifying any causal factors. The sparse geographic coverage of the location of the wells made it difficult to make additional use of these data and the analysis was terminated.
As an indication of the possibility of contamination of Canadian agricultural soils with industrial organic compounds, analyses were conducted on 30 soils from different provinces. Very low or not detectable levels of most industrial organic chemicals were found in the agricultural soils analyzed. The exceptions were residues of pesticides currently in use and the detected levels were consistent with their use in crop production and are not known to represent a significant hazard to the environment. Other ubiquitous compounds, such as phthalate esters and polychlorinated biphenols (PCBs) occurred frequently in small amounts. In addition, municipal sludge from Hamilton and Sarnia were incubated with soil to monitor the persistence of chemicals arising from this source. Even though these sludges are thought to represent worst-case industrial organic contamination possibilities, it was concluded that land application of these sludges according to recommended ON practice does not represent a significant hazard from organic chemicals to agriculture and the environment.In an attempt to determine the impact of soil quality change on crop yield and sustainable production, an extensive literature review was conducted and an annotated bibliography of research efforts which focused on the effects of soil degradation on crop productivity was produced. A survey of innovative conservation farmers identified indicators that distinguish between the kinds and severity of soil degradation, determine losses of crop productivity due to soil degradation, and ascertain threshold levels at which ameliorative measures should be taken. These farm-level observations were also applied to a framework for evaluating sustainable land management, and integrated with the scientific studies to provide a rule base for an expert system which would function as a conservation planning and research tool.
Project Development and Coordination
Related Soil Quality Reports