4 Soil Mapping… Why would we want to map soils? Communication of geographic informationTools for land management and planningMany soil scientists specialize in the mapping of soils.
5 Steps in mapping the soil of a given area Define the scale and level of detail that is required.Study existing information regarding the soil, geology, topography, vegetation of the area.Define soil units to be mapped.Compile information about the nature of each soil.Mark boundaries of where each soil unit occurs.
6 Soil sampling in the landscape Soil descriptionUse is made of a soil pit or augered samplesHorizons are identified and characteristics of the soil systematically describedSoil sampling in the landscapeIt is important to understand the way in which landscape, vegetation etc. affects or indicates soil properties to ensure efficient sampling techniques.
7 Soil surveys:Mapping of the soilsCharacterization of mapping units.Classification of mapping units.Correlation with other soil surveys.Interpretation of soil suitability for various land uses.Soil surveys can be done at very different scales (1st order to 5th order; intensive to reconnaisance)
8 How could soil classification and mapping aid those involved in: Engineering and construction?Landcare and conservation?
10 What is soil erosion?“The wearing away of the land surface by running water, wind, ice or other geological agents, including such processes as gravitational creep.”“Detachment and movement of soil or rock fragments by water, wind, ice or gravity.”
11 Different types of water erosion… Accelerated erosionGeological or natural erosionDonga or gully erosionNormal erosionRill erosionSheet erosionSplash erosionTunnel erosion or piping
12 Effects of erosion… On site: Off site: Loss of fertile topsoil Selective removal of organic matter and fine materialLoss of seeds and seedlingsChange in slope topography (unsafe conditions, more difficult remediation, high expense)Change in soil characteristics like permeability, infiltration rate, etc.Off site:Buildup of sediment and water elsewhere in the system
13 The mechanics of soil erosion… DetachmentTransportationDeposition
14 The effects of raindrops: Detach soilDestroy granulationCan lead to crustingTransport of particles in some cases
15 Transport Deposition Rainsplash Running water Sheetwash Gully erosion NB Infiltration capacitySheetwashGully erosionDepositionCan occur over long distances or short distancesAmount of soil delivered to stream divided by the amount eroded = delivery ratio
16 Prediction and modelling of soil erosion… Why would we want to predict soil erosion?Optimal resource managementEvaluation of consequences of different land useCompliance with environmental requirementsDevelopment of sediment control plans (particularly for construction projects)Prediction of dam infiltration rates…
17 What do we need to understand before we can predict erosion? What factors affect soils’ susceptibility to erosion?Erosivity of erosion agents.Erodibility of soils.Length of slope.Gradient of slope.Land cover and management.NB vegetation, plant residues, soil tillageErosion control practices.
18 Erosivity… Total rainfall Intensity and seasonal distribution of the rainWhy is intensity important?Intense rains have large drop sizeHigher rate of rainfall = more runoff
19 Erodibility… Indicates a soil’s inherent susceptibility to erosion Infiltration capacityStructural stabilityProperties that tend to result in high erodibilityHigh fine sand and silt contentExpansive clay mineralsImpervious soil layersBlocky, platy or massive soil structure
20 Properties that lead to low erodibility High organic matter contentNonexpansive claysStrong granular structure