RM of Westbourne Bulletin 99-36 - Agriculture and Agri-Food Canada

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Rural Municipality of Westbourne Information Bulletin 99-36 Page 5SOIL AND TERRAIN OVERVIEWThe Rural Municipality (RM) of Westbourne covers an area of 130891 ha (approximately 14.2 townships) in the southern part of theWestlake district in southern Manitoba (page 3). Gladstone is thelargest population and service centre with smaller concentrations ofpeople resident in Plumas and Westbourne.The climate in the area can be related in part to weather data fromPlumas located in the northern part of the municipality. The meanannual temperature is 2.1C and the mean annual precipitation is517 mm (Environment Canada, 1993). The average frost-freeperiod is 119 days and degree-days above 5C accumulated fromMay to September average 1623 (Ash, 1991). The growing seasonin southern portions of the area is slightly longer and warmer. Anevaluation of growing conditions in this region of Manitoba can berelated to estimates of seasonal moisture deficit and effectivegrowing degree-days (EGDD) above 5C. The seasonal moisturedeficit calculated between May and September is slightly in excessof 250 mm. The estimated effective growing degree-daysaccumulated from May to September range from 1600 in the southto about 1500 in the north (Agronomic Interpretations WorkingGroup, 1995). These parameters provide an indication of moistureand heat energy available for crop growth and are generallyadequate to support a wide range of crops adapted to westernCanada.The Red River Valley and Westlake Till Plain physiographicsubsections occupy the eastern part of the municipality while thewestern portion is in the Lower Assiniboine Delta (Canada-Manitoba Soil Survey, 1980). Elevation in the municipality rangesfrom 310 metres above sea level (m asl) in the southwest corner to213 m on Lake Manitoba. The land surface is level to very gentlyundulating, sloping gradually to the east at a rate of 1.5 metres perkilometre (8 ft per mile). Local relief is generally under 3 metresand slopes are less than 2 percent in the Lower Assiniboine Deltaand the Red River Valley while the subdued ridge and swaletopography of the Westlake Till Plain is characterized by slopes of2 to 5 percent (page 9). Much of the municipality is affected byhigh groundwater levels, particularly near the Big Grass Marsh onthe eastern boundary of the municipality. Surface drainage is viathe Willowbend, Squirrel and Pine Creeks which are tributaries ofthe Whitemud River flowing into Lake Manitoba. A network ofditches assists in removal of surface waters for agriculturalpurposes.Soil materials in the municipality were deposited during the lastglaciation and during the time of glacial Lake Agassiz. The RedRiver Valley section is characterized by loamy to clayey texturedlacustrine and alluvial deposits whereas the Lower AssiniboineDelta is a smooth lacustrine and deltaic area of sandy depositsunderlain by lacustrine clays and glacial till. The Westlake TillPlain is a gently undulating and ridged area of extremely calcareous,waterworked, stony, loam textured glacial till (page 11). Thegenerally flat topography throughout the municipality results in themajority of soils being classified as imperfectly to poorly drained(page 13).Soils in the municipality have been mapped at a reconnaissancelevel (1:126 720 scale) and published in the soil survey reports forthe Carberry (Ehrlich et al., 1957) and West-Lake (Ehrlich etal.,1958) map sheet areas. Detailed 1:20 000 scale map informationis available for western parts of the municipality (Langman, 1984).According to the Canadian System of Soil Classification (SoilClassification Working Group, 1998), imperfectly drained BlackChernozem soils developed on sandy lacustrine materials(Almassipi association), loamy to clay loam lacustrine sediments(Lakeland association), clayey lacustrine sediments (Westbourneassociation) and stony, loam textured glacial till (Isafoldassociation) are dominant. Weakly developed Regosolic soils of theGladstone association occur on variably textured alluvium.. Poorlydrained sites throughout the area are classified as Humic Gleysols.Major management considerations are related to texture (sandy andclayey soils) and wetness (page 15). Seasonal high water tables (at1 to 2 metres) and saturated soils are common. Surface water pondsin poorly drained depressional areas and soils adjacent to the BigGrass Marsh are subject to flooding in wet years. The sandy soils
Page 6 Information Bulletin 99-36 Rural Municipality of Westbourneof the Lower Assiniboine Delta are subject to potential wind erosionand droughtiness and the glacial till soils are moderately toexcessively stony. Soils throughout the municipality are generallynon-saline except for scattered occurrences of weak salinity in theWestbourne soils.Just over 3 percent of the soils are rated Class 1 for agriculturalcapability and 49 percent are rated in Class 2. Soils affected byincreasing severity of droughtiness, wetness and stoniness are ratedas Class 3 and cover 23 percent of the area. Nearly 14 percent ofthe soils are placed in Class 4, primarily due to sandy texture andlow moisture holding capacity. About 4 percent of the soils arerated in Class 5 due to excess wetness while soils affected byextreme droughtiness and excess wetness rated in Class 6 occupyless than 2 percent of the area. Organic soils which have verylimited capability for agriculture in their native state cover 5 percentof the area (page 17). The irrigation suitability (page 19) of the soilsvaries from Good (39 percent) to Fair (35 percent) and Poor (21percent).One of the issues currently receiving considerable attention is thesustainability of agricultural practices and their potential impact onthe soil and groundwater environment. To assist in highlighting thisconcern to land planners and agricultural producers, an assessmentof potential environmental impact (EI) under irrigation shown onpage 21 varies from Minimal on the clayey soils to Low on the tillsoils and Moderate on the loam to clay loam textures. Sandy soilsin the Lower Assiniboine Delta with high permeability and typicallyhigh watertables are at High potential risk. This EI map is intendedto be used in association with the irrigation suitability map.Another issue of concern to producers, soil conservationists andland use specialists is soil erosion caused by agricultural croppingand tillage practices. Areas with potential for water erosion areshown on page 23. The glacial till soils and the sandy lacustrinesoils, together occupying about 40 percent of the land area, areestimated to have a Negligible risk of degradation due to watererosion. Water erosion risk varies from Low on the clayey soils toModerate on loam textured soils. However, the sandy soils are ata greater risk of erosion by wind. Current management practicesfocus on maintaining adequate crop residues to provide sufficientsurface cover to adequately protect the soils from both wind andwater erosion.Agriculture is the dominant land use in the RM of Westbourne. Anassessment of the status of land use in 1994, obtained through ananalysis of satellite imagery, showed annual crops occupying 60percent of the area, forages nearly 2 percent, grasslands about 27percent and treed areas 5 percent. The grassland and treed areasprovide forage and grazing capacity as well as wildlife habitat.Wetlands occupy between 2 and 3 percent of the area and alsoprovide wildlife habitat. Various non-agricultural uses such asinfrastructure for urban areas, transportation and recreation occupyabout 3 percent of the municipality (page 25).The majority of soils in the RM of Westbourne have moderate tomoderately severe limitations for arable agriculture. The claytextured soils require management practices which maintainadequate surface drainage, soil structure and tilth and the sandy soilsrequire protection against wind erosion. This includes leavingadequate crop residues on the surface during the early spring period,provision of shelter belts and use of minimum tillage practices andcrop rotations which include forages. A major portion of themunicipality has low relief and a dominance of imperfectly topoorly drained soils. These soils are frequently saturated andsubject to surface ponding, particularly during spring runoff orfollowing heavy rains. Consequently, improvement andmaintenance of water management infrastructure on a regional basisis required to reduce surface ponding while maintaining adequatesoil moisture for crop growth.
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RM of Westbourne Bulletin 99-36 - Agriculture and Agri-Food Canada

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