Rates of soil redistribution associated with Soil Zones and slope classes in southern Saskatchewan

Non-Peer ReviewedUsing 137Cs redistribution techniques we examined the relationship between mean rates of soil redistribution and average slope characteristics at twenty-one areas in the Brown, Dark Brown, and Black Chernozem Soil Zones of southern Saskatchewan. Net soil losses averaged 5.8 t ha-1 yr-1 for areas with mean gradients between 0 and 1.5°, 7.8 t ha-1 yr-1 for areas with mean gradients between 1.0 and 3°, and 11.3 t ha-1 yr-1 for areas with mean gradients between 3.5 and 8.5°. For all three slope classes, the highest rates of soil loss were found in the Dark Brown soil zone and the lowest rates in the Black Soil Zone. Net soil loss alone was, however, an inadequate indicator of the rate of loss within the areas because a considerable proportion of eroded soil was deposited within the confines of the study areas

Temporal denitrification at the landscape scale in a Black soil

Non-Peer ReviewedLandscape scale and seasonal pattern of denitrification activity have to be incorporated in a model to estimate total N losses. A study was conducted to exam the seasonal variability of denitrification in a landscape near Blaine Lake, Saskatchewan. A 120 x 120 m sampling grid, separated by a spacing of 10 m, was established in a Black Chernozem soil. The area was surveyed, landform elements identified and from each landform element ten sampling points were further selected and sampled throughout the season for denitrification activity by the acetylene-blockage approach. Soils samples were taken seven times during the entire 1991 season before the area was prepared for seeding in the spring, following precipitation events during the growing season , and in the fall at the onset of frost. Following incubation, soil samples were analyzed for percent moisture, NH4+ and NO3-, soluble organic carbons, and total soil respiration. The distribution of denitrification activities were highly skewed and followed a distinct landscape pattern that remained consistent throughout the year. Denitrification activity increased significantly after the occurrence of a precipitation event and was further enhanced after the application of fertilizer-N, ceased toward the end of the growing season and became zero at the fall sampling. Moisture was the most dominant parameter controlling denitrification activity followed by the concentration of and NH4+ and NO3-. The highest denitrification activity occurred on the divergent and convergent footslopes, the lowest activity on the divergent shoulder and upper level landform elements, a landscape scale pattern that remained consistent throughout the year, independent of the magnitude of activity. Ambient evolution of N2O and denitrification activity followed predominantly a similar temporal and landscape scale pattern. By estimating the duration of a denitrification following a precipitation event at the various landform elements and correcting for the percentage each landform element occupies in the landscape, the total denitrification per precipitation during the early part of the season was estimated at 357 g N ha-1 cycle-1. In conclusion, results indicates that landscape scale pattern of denitrification remained constant throughout the growing season and was predominantly induced by precipitation events

Spatial pattern of soil properties in an irrigated field

Non-Peer ReviewedDenitrification from agricultural ecosystems is regarded as a major contributor to atmospheric N levels, but the actual rates of denitrification and the controls on these rates remain poorly understood. This study was conducted to examine landscape-scale patterns of denitrification and the soil properties that control these patterns. Two sampling grids (11 x 11 m and 110 x 110 m) were established in an irrigated field in an aridic Boroll (Brown Chernozemic) soil in southern Saskatchewan. The measured soil properties (denitrification rate, respiration rate, volumetric moisture content, bulk density, soluble organic and inorganic carbon, total and mineral N, in situ pH, and in situ redox potential) were correlated to slope properties and derived landform elements at the site to determine landscape-scale patterns and relationships. The soil properties occurred in one of three spatial patterns: (i) a random pattern for mineral N; (ii) a diagonal pattern for pH, soluble organic and inorganic carbon, and total N; and (iii) a depression-centered pattern for denitrification, bulk density, moisture, respiration and redox potential. Statistically distinct rates of denitrification were associated with the different landform elements: rates were lowest in the shoulder elements, intermediate in the footslope and level-convex elements, and highest in the level-concave elements. Hot-spots of denitrification activity, i.e., sampling sites with denitrification rates statistically identified as outliers, were all associated with the level elements and, predominantly, the level-concave elements

Rates of denitrification as influenced by irrigation

Non-Peer ReviewedThe rate of denitrification, using the acetylene blockage method, was determined before and after irrigation at two sites; at Birsay on a clay-loam soil and at Outlook on a sandy soil. At Birsay, 110 kg N/ha as urea was applied 10 days before seeding and an additional 4 kg N/ha as ammonium phosphate at time of seeding. At Outlook, 50 kg N/ha as ammonium nitrate was applied just before seeding. Before irrigation, the rate of denitrification at both sites was almost undetectable. A sharp increase in the rate, however, occurred at both sites within a few hours after irrigation (approximately 25 mm) and lasted for approximately 24 hrs and 12 hrs at Birsay and Outlook, respectively. At the time of maximum activity, the losses of N (N2O and N2) were estimated to be 50 g ha-1 hr-1 and 3 g ha-1 hr-1 at Birsay and Outlook, respectively. The total amount of N lost per irrigation cycle, due to denitrification, at Birsay and Outlook were calculated to be 730 g ha-1 and 21g ha-1, respectively. The difference in the amount of N2O evolution at the two sites is partially attributed to the difference in soil type. The water holding capacity at Outlook is lower as compared with the soil at Birsay. Subsequently, the degree of anaerobic conditions, a pre-requisite for denitrification, will be less at Outlook. A lag period of 20 hrs occurred between the application of water and the maximum evolution of N2O of incubated soil cores. This was determined by analyzing incubated soil cores repeatedly over a period of 48 hrs. As the increase in denitrification at Birsay lasted for 24 hrs after the application of water, the maximum rate of denitrification did occur under those field conditions at Birsay. At Outlook, however, where the increase in denitrification only lasted for 12 hrs, the maximum rate of denitrification was not obtained under the existing field conditions. There were 10 irrigation and 7 precipitation events which caused denitrification. According to the percentage of the landform elements and its proper denitrification activity, the total N lost per year at Birsay was estimated to be 120 kg ha-1

Rates of denitrification as influenced by irrigation

Non-Peer ReviewedThe rate of denitrification, using the acetylene blockage method, was determined before and after irrigation at two sites; at Birsay on a clay-loam soil and at Outlook on a sandy soil. At Birsay, 110 kg N/ha as urea was applied 10 days before seeding and an additional4 kg N/ha as ammonium phosphate at time of seeding. At Outlook, 50 kg N/ha as ammonium nitrate was applied just before seeding. Before irrigation, the rate of denitrification at both sites was almost undetectable. A sharp increase in the rate, however, occurred at both sites within a few hours after irrigation (approximately 25 mm) and lasted for approximately 24 hrs and 12 hrs at Birsay and Outlook, respectively. At the time of maximum activity the losses of N (N2O and N2) were estimated to be 50 g ha-1 hr-1 and 3 g ha-1 hr-1 at Birsay and Outlook, respectively. The total amount of N lost per irrigation cycle due to denitrification at Birsay and Outlook were calculated to be 730 g ha-1 and 21 g ha-1, respectively. The difference in the amount of N2O evolution at the two sites is partially attributed to the difference in soil type. The water holding capacity at Outlook is lower as compared with the soil at Birsay. Subsequently, the degree of anaerobic conditions, a prerequisite for denitrification, will be less at Outlook. A lag period of 20 hrs occurred between the application of water and the maximum evolution of N2O of incubated soil cores. This was determined by analyzing incubated soil cores repeatedly over a period of 48 hrs. As the increase in denitrification at Birsay lasted for 24 hrs after the application of water, the maximum rate of denitrification did occur under those field conditions at Birsay. At Outlook, however, where the increase in denitrification only lasted for 12 hrs, the maximum rate of denitrification was not obtained under the existing field conditions. There were 10 irrigation and 7 precipitation events which caused denitrification. According to the percentage of the landform elements and its proper denitrification activity, the total N lost per year at Birsay was estimated to be 120 kg ha-1

Spatial and temporal variations of N2O evolution at the landscape-scale as affected by land use

Non-Peer ReviewedNitrous oxide has been widely recognized as a major scientific and environmental issue because of its involvement in global warming and destruction of the atmospheric ozone layer. Soils generally act as source of N2O, but the actual rates of N2O emission and the controls on these rates remained poorly understood. As a pre-requisite to quantify large-scale N2O emissions over a long term range, this study was conducted to determine the landscape- and seasonal-scale patterns of N2O emission. Nitrous oxide emissions were assessed at a hummocky glacio-lacustrine landscape in the Black soil zone. The study area was divided into three agronomic practices: an unfertilized canola site, a conventional fallow site, and a pasture site. A systematic grid design was employed at each site and N2O emission was monitored using closed chamber method. A clear landscape-scale pattern of N2O emission was observed in the unfertilized canola and conventional fallow sites; lower landscape positions showed higher N2O flux than the upper landscape positions. This pattern remained consistent throughout the season, with increased in N2O flux towards the mid-growing season (summer), decreased towards the end of the growing season (early fall), and virtually ceased by the onset of frost (late fall). Of the three sites tested, the pasture site showed the lowest N2O emission and activity was only observed during the summer samplings. Soil respiration and moisture content followed. similar spatial and temporal patterns as N2O emission. Results indicate that N2O production is controlled at the landform level by soil factors and at seasonal level by precipitation and temperature. Such relationships might be useful in generating a spatially-distributed model for quantifying N2O emission

Nitrogen accumulation by pea as affected by topography

Non-Peer ReviewedField peas grown under normal field conditions are exposed to variable soil and environmental conditions that will affect both crop yield and nitrogen (N) uptake. Topography and slope position may play an important role in governing soil and environmental factors that influence N accumulation. In 1991, a field experiment was initiated to examine the effects of landscape position on the yield and N accumulation by field pea (var. Marofat). A two-hectare site was located in the Black Soil Zone on land with gently sloping to roughly undulating slopes (2-5 %). Six landform elements were identified at the site location. The site was managed at a farm scale using typical cultural practices. Spring levels of inorganic nitrogen (NO3 + NH4) ranged from 19.0 to 57.4 kg/ha (0-60 cm depth). Differences in levels of inorganic nitrogen between landform elements were observed (p = 0.03). Volumetric moisture content of the soil (0-120 cm) was consistently highest in footslopes throughout the growing season. Water stress was not a limiting factor to plant growth in any landform until 50-55 days after planting. Total yield (seed + straw) of the pea crop ranged from 2310 to 8100 kg/ha while seed yield varied from 960 to 3940 kg/ha. Significant differences between landforms were detected for total yield (p = 0.02) but not seed yield. Seed nitrogen content ranged from 31-133 kg/ha but no differences were observed between landforms

The use of large undisturbed cores to assess soil quality-yield relationships in the greenhouse

Non-Peer ReviewedLarge undisturbed cores were taken from different landscape positions (divergent shoulders, DSH, and convergent footslopes, CFS) at two sites in the Black soil zone. The soils are classified as belonging to the Oxbow association and have been cultivated for 15 and 82 years. The cores were used in a greenhouse experiment to study the effect of soil quality on yield of spring wheat (var. Katepwa) at three levels of simulated growing season precipitation: low (123 mm season-1), mid (189 mm season-1), and high (332 mm season-1). Grain yields in the DSH cores increased with increasing precipitation for both the 15- and 82-year soils. Moreover, the 15-year DSH cores out-yielded their 82-year counterparts by 50, 76, and 85% at the low, mid, and high water levels, respectively. Cores from the CFS positions were watered only at the mid-water level. Grain yields in the 15- and 82-year CFS cores and the 15-year DSH cores were not significantly different (P < 0.05). The results of this study indicate that soil quality is a relatively minor factor when water is limiting but assumes a much greater role in years of normal or above normal growing season precipitation. These initial results also suggest that large cores are a feasible and cost-effective means of studying soil-plant relationships in the greenhouse or growth chamber

Spatial variability of deep leached nitrate as related to denitrification in a prairie landscape

Non-Peer ReviewedDenitrification is an anaerobic process that converts NO3- to N2 and N2O, and is considered one of the most highly variable soil processes within a landscape. Moisture acting in response to hillslope hydrological processes controls rates of denitrification and leaching at the landform level. In 1991, a field study was conducted in the Black Soil Zone of an undulating landscape (3-5% slope) at Blaine Lake, Saskatchewan to determine the amount of nitrate leached below the rooting zone and its possible relationship to denitrification. Nitrate has been leached and translocated in the upper regolith in response to water movement where significant leaching of soluble components occurred in depressional areas to depths beyond 3 m. The amount of nitrate at depth was greatest in shoulder and upper level elements where it reached a maximum of 95 ug g-1 at the 1.5 m depth. Footslope and lower level elements contained the lowest nitrate levels (<1 ug g-1) within the 3m sampled area. High rates of denitrification occurred in footslope and lower level elements, compared to significantly lower rates on divergent shoulder and upper level elements. Nitrate content at depth was inversely correlated with denitrification activity (-0.485 ***). High mean concentrations of nitrate were therefore, spatially related to low rates of denitrification activity in response to hydrological spatial variation

Short term effect of breaking and cultivation on properties of an Oxbow landscape

Non-Peer ReviewedChanges in soil quality over the first six years of cultivation were studied for an Oxbow landscape dominated by Black Chernozems. Bulk density at shoulder, footslope, and level landforms was found to increase by 15-20 % from 1985 to 1988 and by 3-4 % from 1988 to 1991. Similarly, organic carbon concentration declined by 17-37 % and 0-10 %, respectively, over the same periods. These results demonstrate that cultivation of virgin land has an almost immediate impact on soil quality. 137Cesium measurements indicated that appreciable soil erosion has not occurred in this landscape since cultivation began