Soil water storage benchmarking for environmental monitoring

Non-Peer ReviewedSoil water, a key hydrological factor, controls the fate and transport of nutrients and pollutants in soil as well as emission of green house gases from soil. Inherent spatial variability of soil water requires multiple monitoring sites for soil water which is expansive in terms of money, time and labour. The objective of this study was to identify the hydrologically time stable location (benchmark point) and spatial pattern of soil water storage in a hummocky landscape in semiarid climate. Soil water was measured in field for consecutive two years (11 measurements) by Neutron Moisture Meter (NMM) along a 128 point transect established at St Denis National Wildlife Area, Saskatchewan, Canada. Soil water measurements were taken at every 20 cm up to the depth of 1.2 m at every 4.5 m on the transect. The NMM was calibrated for this site and the calibration equation was used to calculate the soil water storage at different depths. High Spearman’s rank correlation coefficient between different dates of measurements indicated the spatial similarity of soil water storage pattern over time. Similar environmental events showed more persistent spatial pattern between measurements than different environmental events. The stability or the similarity of the rank of individual observations in the probability distribution functions over time indicated temporal stability of soil water storage pattern. While, 22nd point from the origin of the transect maintained the rank of soil water storage overtime for 0-20 cm with very low measurement variability, 4th point maintained the rank for 0-60 cm and 0-120 cm depth. The similarity or persistency of rank in water storage pattern and the mean water content over field at multiple times helped in identifying representative moisture benchmark site, which can be used for environmental monitoring and modelling, irrigation scheduling, nutrient recommendations and predicting green house gasses

Representative benchmark site identification for soil moisture storage

Non-Peer ReviewedSoil moisture limits agricultural production in semi-arid prairies and is a key hydrological factor affecting the fate and transport of pollutants in soils. Spatial and temporal variability in soil water requires monitoring many locations to capture the salient features of soil water in the field. The objective of this study was to examine whether there are temporally stable soil moisture patterns in a field and whether a representative moisture benchmark site can be identified from these patterns. The experiments were conducted on a black soil at Alvena, northwest of Saskatoon, Canada. Soil moisture was monitored at 95 measurement sites with a portable Capacitance Probe (CP) along a 612m rolling transect, from April to September in 2001 and 2002. Temporal stability of spatial patterns in soil moisture for depths of 30, 60, 90, 120 and 160cm were determined using temporal means and standard deviations of the differences between individual and spatial average values of soil moisture along the transect. The spatial patterns of soil water storage were stable in different locations for each depth. Spatial variations in soil moisture with daily soil moisture means of >0.20 and <0.20 showed poor correlations with soil texture (R2 < 0.1) and topographical variables (R2 < 0.3). Clay content showed the least amount of control of spatial patterns with only one day with R2 (=0.08) greater than 0.01. Coefficient of variation and standard deviation of soil moisture both decreased with increasing soil moisture. For depths of 30, 90, and 120cm, benchmark sites had a difference of less than 1% in soil moisture storage from both measured field mean and a composite sample obtained using the conventional random sample method, indicating the three methods are equivalent to each other. Soil moisture benchmark sites identified in this study represent field mean soil moistur

Preferential transport of Escherichia coli through soil

Non-Peer ReviewedContamination of water sources resulting from Escherichia coli 0157:H7 movement through the soil requires knowledge of the transport mechanisms. The objective of this study was to examine the effect of initial soil water content on the preferential transport of E. coli through the soil. The study was conducted on a heavy clay soil near Plenty, SK. Escherichia coli as well as conservative and adsorptive tracers were applied to treatments that were initially dry, partially wet, and initially wet. Relative breakthroughs of E. coli and Cl- were similar for all three treatments, showing a large proportion of the mass applied remained in the top 10 cm of soil, indicating transport through the soil matrix. Beyond this depth, E. coli: Cl- ratios remained consistent, suggesting transport along preferential pathways. The lack of differences between treatments may suggest that irrespective of the transport pathway, the end result is the same. This study is important for semi-arid areas where dry cracked soils can receive intense thunderstorms that provide enough water to transport E. coli to substantial depths

Determination of soil hydraulic properties in non-level landscapes

Non-Peer ReviewedMajority of the landscapes in Saskatchewan are non-level. However, specifically designed instruments are not available for the estimation of hydraulic properties of surface soils in non-level landscapes. The purpose of this study was to evaluate the suitability of available tools (tension infiltrometer and double ring infiltrometer) for the estimation of surface soil hydraulic properties in non-level lands. A field experiment was conducted in a loamy soil in Laura, Saskatchewan. Soil surface was prepared to represent 0, 7, 15 and 20% slopes. Infiltration rates were measured using a tension infiltrometer and a double ring infiltrometer. Hydraulic properties were estimated. Steady infiltration rates measured using double ring infiltrometer were not significantly different among slopes (p < 0.05). Saturated hydraulic conductivity and inverse macroscopic capillary length scale predicted from tension infiltrometer were not statistically different (p < 0.05) among the slopes tested indicating that these instruments are suitable for characterization of surface hydraulic properties in hummocky landscapes in Saskatchewan. A computer simulation is planned for further confirmation of these results

Determination of hydrophobicity index: standard and mini disk infiltrometers

Non-Peer ReviewedSoil hydrophobicity drastically impacts water infiltration, retention and transport. Hydrophobicity index, a ratio of the sorptivity of water to ethanol, is a common measure of soil hydrophobicity. The sorptivity may be measured using the disk infiltrometer. The standard disk infiltrometer is large, cumbersome and expensive while the mini disk infiltrometer is compact and readily accessible. The objective of this study was to determine if the mini disk infiltrometer is comparable to the standard disk infiltrometer as a means of analyzing the soil hydrophobicity index. The soil hydrophobicity index was calculated from the sorptivities of water and ethanol as determined by both infiltrometer methods. Results indicate no statistical difference between soil hydrophobicity indices calculated from the standard and mini disk infiltrometer methods

Representative sampling size and number of required samples for soil testing in direct seeding fields

Non-Peer ReviewedDirect seeding is widely utilized in the southern Canadian prairies. The associated band application of fertilizers makes conventional soil testing problematic. Strip sampling was suggested in direct seeding fields, but little is known about the optimum strip length. The objective of this study was (1) to identify the representative sampling size (RSS) of a sampling strip and (2) to determine the number of required samples (NRS) in a field in terms of point-based random sampling. Soil samples of 0-10 cm and 10-20 cm were collected from two 10 acre farm fields near Central Butte in the Brown soil zone of Saskatchewan. For strip sampling, five 160 cm long and 10 cm wide sampling strips were selected in these two fields. Different samples with sampling lengths ranging from 5 cm to 155 cm were obtained. For random sampling, 30 and 45 samples using a 4 cm diameter tubular probe were collected in these two fields. The results showed that RSSs differed with fields, nutrient types and soil layers. On average, the RSSs were 60 cm, 65 cm and 35 cm, respectively for testing NO3--N, NH4+-N and extractable P. The NRSs differed with sampling fields but not with nutrient types and soil layers. With a confidence level of 95%, about 30 and 80 random samples are needed in these two fields, respectively, to achieve mean estimate of soil nutrients with a relative error of 10%. This study provided a reference of soil sampling for soil nutrient tests in direct seeding fields

Topography affects grassland heterogeneity

Non-Peer ReviewedDetermining and monitoring ecosystem heterogeneity and biodiversity is important for grassland management and can be carried out through remote sensing such as satellite images. However, in rolling landscapes, biophysical properties of ecosystems, the indicators of heterogeneity and biodiversity are highly scale and location dependent and little research is reported on how topography affects biophysical properties of ecosystems quantitatively. The objective of this study is to examine how topography affects spatial biophysical variation using statistics and a wavelet approach in the mixed grassland ecosystem, Saskatchewan, Canada. Field leaf area index (LAI) was collected with an LAI-2000 instrument and topographical data were measured using a total station along five paralleled transects. Results showed that biophysical spatial variation is highly topography-controlled, and the wavelet approaches can be used to identify the spatial heterogeneity of a grassland ecosystem at different scales. This study suggests the potentials of using readily-available topography data to guide the ecosystems management and selection of the resolution of satellite images

Effects of different land use on soil hydraulic properties

Non-Peer ReviewedAn understanding of hydraulic properties of surface soils is needed for sound soil management because it determines the partition of rainfall and snow melt into runoff or soil water storage. The purpose of this study was to evaluate the effects of three land uses (native grassland, brome grassland and cultivated land) on soil physical properties. For each land use, water infiltration rates were measured with a tension infiltrometer at 3, 7, 15, and 22 cm water tensions. Total porosity and macro porosity were determined and hydraulic properties were estimated. The highest total porosity and macro porosity were observed in native grassland while cultivation had significantly reduced macro porosity. At 15 and 22 cm tensions native grassland had significantly lower infiltration rates than cultivated fields while brome grassland had intermediate infiltration rates. Surface soil hydraulic properties differ markedly among land uses, with grasslands having higher saturated hydraulic conductivity. The observations indicate that cultivated soils have lower macroporosity than grassland soils and, therefore, lower infiltration of rain and increased potential for runoff. In contrast, cultivated soils are able to absorb more rainfall and snow melt under unsaturated conditions. Land use changes may alter the water balance of the area by changing the amount of surface runoff and therefore, any changes in existing land use must be done cautiously

An evaluation of soil water use efficiency for different seeding row spacing and stubble height

Non-Peer Reviewe

Can the quality of soil structure be maintained following repeated applications of high rates of hog manure?

Non-Peer ReviewedThe long-term impact of repeated applications of high rates of liquid hog manure on the quality of the soil and that of the environment is not well known. For optimal application rates of hog manure, improved knowledge is essential regarding the long-term effect of hog manure applications on salinity, acidity, soil density, aggregation, and soil strength. A field research project was initiated in 1998 to determine the effects of repeated application of high rates of injected swine manure (up to 13,000 g ac-1) on soil quality in Southern Saskatchewan. In the fall 2001, measurements were made on different soil physical and chemical quality indicators in two of the sites with contrasting soil types: a heavy clay textured soil in the Dark Brown Soil Zone and a sandy loam to loam textured soil in the Brown Soil Zone. At the site with heavy clay textured soil, the high rates of liquid hog manure increased sodium absorption ratio (SAR), electrical conductivity (EC), and surface penetration resistance (SPR) and decreased soil pH; whereas, there were no significant changes on the quality of the surface soil at the sandy loam to loam textured soil to date other than a decrease in surface crusting index. Studies are in progress to include additional sites and also additional soil quality indicator parameters through a longer term monitoring program