No abstract

Mapfumo, E., Chanasyk, D. S., Naeth, M. A. and Baron, V. S. 1999. Soil compaction under grazing of annual and perennial forages. . This study investigated the impact of heavy, medium and light grazing of meadow bromegrass an triticale on soil bulk density, relative compaction and penetration resistance. The study was conducted at Lacombe, Alberta, on a Orthic Black Chernozem of loam to silt loam texture. Sampling was conducted in fall 1995, spring 1996, fall 1996 and spring 1997. Core samples to a 15-cm depth were collected for measurement of bulk density and moisture content. Penetration resistance to 15 cm was measured with a hand-pushed cone penetrometer. The standard Proctor test was used to determine maximum bulk density. Relative compaction was the ratio of actual bulk density to the Proctor maximum bulk density expressed as a percentage. Surface (0-2.5 cm) bulk density and penetration resistance were significantly greater under heavily grazed than under medium and lightly grazed meadow bromegrass only for fall 1995. Differences in bulk density, relative compaction and penetration resistance for different grazing intensities in spring and fall 1996 and spring 1997 were either small or not significant. Generally, bulk density decreased over winter in the top 2.5 cm, was not consistent in the 5-to 10-cm depth interval and did not change in the 10-to 15-cm interval. Except in fall 1995, the relative compaction values for all grazing intensities and forage species were less than 90%, a value considered critical for plant growth. Generally, within each grazing level, there were minimal differences in bulk density, relative compaction and penetration resistance under triticale compared to those under meadow bromegrass.Key words: Bulk density, relative compaction, penetration resistance Mapfumo, E., Chanasyk, D. S., Naeth, M. A. et Baron, V. S. 1999. Compaction du sol due à la pâture des fourrages annuels ou perennes. 79: 191-199. L'objet de nos travaux était d'examiner les effets d'une paissance intense, moyenne ou légère de pâturages de brome des prés et de triticale sur la densité apparente, sur la compaction relative et sur la résistance à la pénétration du sol. L'expérience avait lieu à Lacombe, en Alberta, sur tchernozem noir orthique, de texture variant du loam franc au loam sableux. Le prélèvement des échantillons de sol était effectué à l'automne 1995, au printemps 1996, à l'automne 1996 et au printemps 1997. Des carottes de sol (15 premiers cm) étaient également prélevées pour la mesure de la densité apparente et de la teneur en eau du sol. La résistance à la pénétration jusqu'à la profondeur de 15 cm était mesurée au moyen d'un pénétromètre à cône manuel. Le test standard de Proctor servait à déterminer la densité apparente maximale. La compaction relative correspondait au rapport entre la densité apparente mesurée et la densité apparente maximale déterminée au test Proctor. La densité apparente et la résistance à la pénétration de la couche superficielle (0-2,5 cm) ne produisait des valeurs significat...

Large amounts of terrestrial organic C and N reserves lie in salt-affected environments, and their dynamics are not well understood. This study was conducted to investigate how the contents and dynamics of 'native' organic C and N in sandy soils under different plant species found in a salt-affected ecosystem were related to salinity and pH. Increasing soil pH was associated with significant decreases in total soil organic C and C/N ratio; particulate (0.05-2 mm) organic C, N and C/N; and the C/N ratio in mineral-associated (<0.05 mm) fraction. In addition, mineral-associated organic C and N significantly increased with an increase in clay content of sandy soils. During 90-day incubation, total CO 2 -C production per unit of soil organic C was dependent on pH [CO 2 -C production (g kg -1 organic C) = 22.5 pH -119, R 2 = 0.79]. Similarly, increased pH was associated with increased release of mineral N from soils during 10-day incubation. Soil microbial biomass C and N were also positively related to pH. Metabolic quotient increased with an increase in soil pH, suggesting that increasing alkalinity in the salt-affected soil favoured the survival of a bacterial-dominated microbial community with low assimilation efficiency of organic C. As a result, increased CO 2 -C and mineral N were produced in alkaline saline soils (pH up to 10.0). This pH-stimulated mineralization of organic C and N mainly occurred in particulate but not in mineral-associated organic matter fractions. Our findings imply that, in addition to decreased plant productivity and the litter input, pH-stimulated mineralization of organic matter would also be responsible for a decreased amount of organic matter in alkaline salt-affected sandy soils.

Abstract:Grazing is common in the foothills fescue grasslands and may influence the seasonal soil-water patterns, which in turn determine range productivity. Hydrological modelling using the soil and water assessment tool (SWAT) is becoming widely adopted throughout North America especially for simulation of stream flow and runoff in small and large basins. Although applications of the SWAT model have been wide, little attention has been paid to the model's ability to simulate soil-water patterns in small watersheds. Thus a daily profile of soil water was simulated with SWAT using data collected from the Stavely Range Sub-station in the foothills of south-western Alberta, Canada. Three small watersheds were established using a combination of natural and artificial barriers in 1996-97. The watersheds were subjected to no grazing (control), heavy grazing (2Ð4 animal unit months (AUM) per hectare) or very heavy grazing (4Ð8 AUM ha 1 ). Soil-water measurements were conducted at four slope positions within each watershed (upper, middle, lower and 5 m close to the collector drain), every 2 weeks annually from 1998 to 2000 using a downhole CPN 503 neutron moisture meter. Calibration of the model was conducted using 1998 soil-water data and resulted in Nash-Sutcliffe coefficient (EF or R 2 ) and regression coefficient of determination (r 2 ) values of 0Ð77 and 0Ð85, respectively. Model graphical and statistical evaluation was conducted using the soil-water data collected in 1999 and 2000. During the evaluation period, soil water was simulated reasonably with an overall EF of 0Ð70, r 2 of 0Ð72 and a root mean square error (RMSE) of 18Ð01. The model had a general tendency to overpredict soil water under relatively dry soil conditions, but to underpredict soil water under wet conditions. Sensitivity analysis indicated that absolute relative sensitivity indices of input parameters in soil-water simulation were in the following order; available water capacity > bulk density > runoff curve number > fraction of field capacity (FFCB) > saturated hydraulic conductivity. Thus these data were critical inputs to ensure reasonable simulation of soil-water patterns. Overall, the model performed satisfactorily in simulating soil-water patterns in all three watersheds with a daily time-step and indicates a great potential for monitoring soil-water resources in small watersheds.

No abstract