Soil Management Guide
 

Glossary

Agriculture capability is a 7 class rating of mineral soils based on the severity of limitations for dryland farming. This system does not rate the productivity of the soil, but rather its capability to sustain agricultural crops based on limitations due to soil properties and landscape features and climate. This system is usually applied on a soil polygon basis and the individual soil series are assessed and maps portray the condition represented by the dominant soil in the polygon. Class 1 soils have no limitations, whereas Class 7 soils have such severe limitations that they are not suitable for agricultural purposes.

Air dry is the amount of water remaining in soil after drying at room temperature for several hours.

Available water holding capacity (AWHC) describes how much available water a fixed amount of soil can hold for plant uptake. It is largely determined by soil texture and to a limited degree by soil structure and organic matter content.

Available water (AW) is the amount of water held in a soil that plants can use. The maximum amount of available water held in a soil is the difference between the permanent wilting point and field capacity, expressed in inches or millimeters of water per unit depth of soil.

Bulk density is the apparent density of a soil, measured by determining the oven-dry mass of soil per unit volume. The volume of soil is determined using sampling cores and is measured before soil is oven-dried to avoid any changes in volume due to drying. Bulk density is usually expressed in g/cm³ or Mg/m³.

Catena is a sequence or family of related soils located in the same climatic zone formed from similar parent material under different landscape positions resulting in different profile characteristics.

Conservation tillage systems include reduced tillage and zero tillage and produce benefits such as soil quality enhancement (increased soil organic matter levels over time), moisture conservation, erosion control, reduced use of fossil fuels and a reduced labour requirement. Weed control in these systems may require increased use of herbicides.

Conventional tillage is a system that traditionally uses moldboard plows or chisel plows with sweeps, followed by discing, harrowing or other secondary tillage operations to incorporate residue, prepare a seedbed and control weeds.

Detailed soil survey maps (see also Soil Survey and Reconnaissance Soil Surveys) identify more of the variation in soil types across smaller landscapes. Detailed soil survey maps are much more accurate and reliable for making decisions at the farm-level. Maps prepared at a 1:20,000 scale (3.2 inches to 1 mile) require 25-30 inspection sites per section of land whereas semi-detailed maps at 1:50,000 scale, or 1.5 inches to 1 mile, require 16 inspections per section.

Direct seeding is a type of reduced tillage where the only tillage operation occurs at seeding. Maximum surface residue is maintained until seeding, at which time high disturbance seed openers are used for seedbed preparation, residue management and weed control.

Discharge zone is an area where the zone of saturation is at or near the surface and the net movement of water is towards the ground surface. Discharge may be focused in areas such as springs, weeping embankments and baseflow discharge, or it may be diffuse over larger areas of the landscape. These areas may be characterized by soils that are calcareous, imperfectly or poorly drained and have a build-up of salts.

Electrical conductivity (EC) is a measure of soluble salts within the soil. EC is expressed in dS/m, mS/cm or mmho/cm (all equal). Electrical conductivity is directly related to the total dissolved solids in the soil.

Eutrophication is the enrichment of water bodies by nutrients, particularly nitrogen and phosphorus. Phosphorus is the nutrient that most commonly limits plant growth in fresh water bodies. Excess P entering water can result in increased production of algae and other aquatic plants, thereby affecting the quality of water and the diversity of organisms present.

Field capacity (FC) is the maximum amount of water held in a soil, measured a few days after it has been thoroughly soaked and allowed to drain freely.

Gleying is a soil-forming process which occurs under poor drainage conditions, resulting in the production of grey colours and mottles.

Gravimetric soil moisture (W%) = [wt. (wet soil) – wt. (oven dry soil)] x 100% / wt. (oven dry soil)

High disturbance openers are medium and wide openers, such as wide hoes, narrow sweeps or shovels, wide spoons, wide shovels and discers. These openers disturb more than 33% of the soil surface.

Hydraulic conductivity is the rate at which water can pass through a soil material usually measured under saturated conditions.

Infiltration is the entry of water into soil. The rate of infiltration can be relatively fast, especially as water enters into pores and cracks of dry soil.

Irrigation suitability is a general suitability rating for irrigated crop production. This classification system considers soil and landscape characteristics such as texture, drainage, depth to water table, salinity, geological uniformity, topography and stoniness and ranking them in terms of their sustained quality due to long term management under irrigation.

Liquid limit is the moisture content at which a soil begins to flow and behave like a liquid.

Loams are medium textured soils made up of a mixture of sand, silt and clay.

Low disturbance openers are narrow openers such as knives, narrow spoons, narrow hoes and slightly offset discs (not including a discer). The openers should not disturb more than 33% of the soil surface area.

Map units are symbols on soil survey maps that represent the type of soil(s) found within a particular polygon. A simple map unit designates a single soil series on a detailed soils map. A complex map unit includes as many as three soil series on a detailed map, or as many as two soil associations on a reconnaissance soil map.

Minimum tillage is a type of reduced tillage that employs a reduction in one or more tillage operations from conventional practices (such as no fall tillage) and uses low disturbance seed openers.

Mottles are rust-coloured spots in the subsoil formed from alternating wetting and drying conditions.

No-till – See zero tillage.

Organic matter is an important component of soil that supplies plants with nutrients, holds soil particles together to prevent erosion, and improves soil tilth. Organic matter also improves water filtration and water-holding capacity while controlling the decomposition and movement of some pesticides. Biological processes of plant growth and human activities, such as tillage, have affected the present state of soil organic matter.

Oven dry occurs when soil has been dried at 105°C for 24 hours so that no water remains.

Parent material is the original material from which soils develop. It is based on the type of bedrock and method of deposition.

Particle density is the grain density, or the mass per unit volume of the soil particles. Pore spaces found in bulk soil samples are excluded. Particle density is usually expressed in g/cm³ or Mg/m³, and the particle density for most agricultural soils is 2.65 g/cm³.

Permanent wilting point (PWP) is the soil water content at which water is no longer available to plants, which causes them to wilt because they cannot extract enough water to meet their requirements.

Plastic limit is the moisture content at which a soil sample changes from a semisolid to a plastic state.

Primary salinity or naturally-occurring salinity results from the long term continuous discharge of saline groundwater.

Recharge zone is an area where water infiltration exceeds the storage capacity of the soil and moves downward to the zone of saturation (groundwater). In recharge areas, well, imperfect and poorly drained soils may have well developed A (leached) and B (clay accumulation) horizons which indicate net movement of water is downward. The surface and subsoil are usually non calcareous.

Reconnaissance (general) soil surveys of Manitoba were started in 1926 as the first step in the development of a basic program of soil research, education, conservation and utilization for the province. Reconnaissance soil surveys are best suited to making general comparisons at the regional scale. The scale is approximately 1:125,000, or 1/2 inch to 1 mile. (See also Soil Survey and Detailed Soil Survey Maps.)

Reduced tillage systems involve the removal of one or more tillage operations to increase residue cover on the soil, reduce fuel costs and to use standing stubble to trap snow to increase soil moisture and permit the winter survival of winter wheat.

Ridge till is a type of reduced tillage where row crops (such as corn) are planted on pre-formed ridges. During the planting operation, crop residues are cleared from the row area and moved to the furrow between rows. The planted rows are on a raised ridge 3 to 5 inches (7.6 to 12.7 cm) above furrows between rows.

Saturated hydraulic conductivity (K_sat) provides the simplest and most consistent means of measuring the rate of water movement through soils.

Saturation is the moisture content at which all soil pores are completely water-filled.

Secondary salinity or human-induced salinity is the result of human activities that have changed the local water movement patterns of an area.

Sensitive areas are areas where productivity is lower (such as eroded knolls or saline areas), and/or in areas that have heightened risk of impacts to soil and water if traditional activities are allowed to continue (such as creeks, potholes, ditches, springs, wells or rapidly permeable areas).

Snow trapping potential (STP) refers to an index which quantifies the amount of standing stubble (height and density) used to capture snow. A snow trapping potential index greater than 20 is acceptable; less than 20 indicate a high risk of winter injury, particularly for winter wheat and triticale. For reference, cereal stubble typically has pre-seed STPs of 80 or higher, while canola and flax are normally in the range of 30-50, depending on the stubble height.

Sodium adsorption ratio (SAR) is the concentration of sodium relative to calcium and magnesium in the soil. SAR is a measure of soil sodicity.

Soil compaction is the squeezing together of soil particles, reducing the space available for air and water. Compaction increases the density of the soil, which hampers infiltration of water, soil air movement, seedling emergence, root growth and ultimately reducing yield.

Soil drainage is the speed and extent of water removal from the soil by runoff (surface drainage) and downward flow through the soil profile (internal drainage).

Soil horizon is a layer of soil running approximately parallel to the land surface and differing from vertically adjacent layers in terms of physical, chemical and biological properties such as colour, structure, texture, pH, etc.

Soil is defined as the collection of natural bodies on the earth’s surface supporting or capable of supporting plants.

Soil phases are variations of a soil series because of factors such as erosion, topography (slope), stones, salinity, improved drainage and peaty layers.

Soil polygon is an area (which can be of any shape) which contains a specific soil condition that is identified by symbol(s).

Soil porosity is the percentage of a given volume of soil that is made up of pore spaces. Soils are oven-dried to measure bulk density, so porosity is a measure of air-filled pore space. % Porosity = [1-(bulk density / particle density)] x 100

Soil salinity is a limitation where plant growth is reduced due to the presence of soluble salts in soil which holds water more tightly than the ability of plants to extract water from the soil.

Soil series is the name given to an individual soil type, with a particular kind and arrangement of soil horizons developed on a particular type of parent material and located in a particular soil zone.

Soil structure refers to the way in which soil particles cling together to form aggregates.

Soil survey is an inventory of the properties of the soil (such as texture, internal drainage, parent material, depth to groundwater, topography, degree of erosion, stoniness, pH and salinity) and their spatial distribution over a landscape (often portrayed in a map).

Soil texture is the relative proportion of sand, silt and clay particles.

Tillage erosion is the progressive downslope movement of soil by tillage causing soil loss on hilltops and soil accumulation at the base of slopes. It is described in terms of erosivity and landscape erodibility. Large, aggressive tillage implements, operated at excessive depths and speeds are more erosive, with more passes resulting in more erosion. Landscapes that are very topographically complex (with many short, steep diverging slopes) are more susceptible to tillage erosion.

Total dissolved solids (TDS) is a measure of soluble salt content in water extracted from a soil sample, expressed in mg/L.

Volumetric soil moisture (Ø) = gravimetric soil moisture x bulk density

Water erosion is the detachment, movement and removal of soil from the land surface by precipitation leaving the landscape as runoff. It can occur naturally, without human intervention, or can be accelerated through human activities such as insufficient residue cover on soils prone to runoff.

Watershed management is the planned use of drainage basins in accordance with predetermined objectives.

Wind erosion is the detachment, movement and removal of soil from the land surface by wind. It can occur naturally, without human intervention, or can be accelerated through human activities such as excessive tillage.

Zero tillage is a type of cropping system in which crops are planted into previously undisturbed soil by opening a narrow slot of sufficient width and depth to obtain proper seedbed coverage. No tillage operation for the purpose of weed control is conducted, but this allows for tillage with low disturbance openers (knives, spikes, etc.) for fall banding of fertilizer, filling in ruts, and the use of heavy harrows for crop residue management.

 

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