| |
Soils | |
| |
|
|
| |
|
|
| |
.
Soil Texture
Mineral particles in soil are grouped into sand (2 - 0.05 mm in diameter), silt (0.05 - 0.002 mm) and clay (less than 0.002 mm in diameter). The proportion of sand (S), silt (Si) and clay (C) particles present in a soil is referred to as texture The presence of larger particles in soil is recognized as gravel, cobbles or stones. Soil texture strongly influences the infiltration of water, the ability of the soil to retain moisture (water holding capacity), its general level of fertility, the tendency to form clods and ease of cultivation. The combination of similar textural classes forms textural groups.
Well-drained soils with loamy sand to sandy loam textures are considered most suitable for potato production. These soils have an adequate capacity to retain water, provide sufficient aeration for root and tuber development and favorable conditions for planting and harvesting. Sound management practices are required to minimize the potential for wind erosion on these soils.
Farmers are successfully producing potatoes on silt loam, sandy clay loam, silty clay loam and clay loam textural classes even though these soils are not considered ideal for potato production. These finer texture soils are prone to water erosion in undulating landscapes, poor to fair internal drainage and soil clod formation if tilled when wet.
A soil that contains a large amount of clay (fine textured soil with more than 35% clay) becomes sticky when wet and lumpy when dry. If this soil is too dry at harvest, it is difficult to separate the soil clods (aggregates) from the potatoes. Tubers harvested from a wet clay soil will also require washing to remove soil particles. These soils are not considered suitable for commercial potato production.
Topography
Topography refers to the percent slope and the pattern or frequency of slopes in different directions in a field. The steeper the slope, the less suitable the field is for potato production. Surface run-off occurs when the amount of water from rainfall or an irrigation application exceeds the rate of infiltration, which is strongly influenced by soil texture. The risk of soil loss is proportional to the length of the slope and the severity of the grade. Medium and fine textured soils are most susceptible to water erosion in sloping landscapes.
Soil Salinity
Salinity refers to the presence of water-soluble salts in soil. Saline refers to a soil condition where water-soluble salts are present in sufficient amounts to affect crop growth. Salinity is measured as the electrical conductivity (EC) and is expressed as deciSiemens/metre (dS/m) or microSiemens/centimetre. The accepted standard is dS/m, however all units of measure are equal. Salinity levels range from less than 4 (non-saline), 4-8 (slightly saline), 8-15 moderately saline and >15 strongly saline. Soils with a reading of less than 4 are most suitable for potatoes. On moderately saline soils, growth and yield of potatoes can be reduced. Leaves may be darker and have burned edges. Plants growing in saline soil are unable to draw water and nutrients, particularly phosphorus, from the soil. Potato production plays a role in soil salinization. The addition of high mounts of irrigation water and fertilizer add significant quantities of salt to the soil. Early detection of salt-affected areas is critical in preventing crop damage or an increase in salinity. A field assessment determining the degree of salinity can be accomplished by soil sampling and analysis or by mapping with an EM38 electromagnetic induction meter. If salinity is a concern, assessments should be conducted every 5 years to determine if salinity is increasing over time. If salinity is detected, growers should implement appropriate water management and cropping practice strategies to improve the productivity of the soil. Prairie Farm Rehabilitation Administration and private soil laboratories provides these service.
Soil pH
Soil reaction, or pH, refers to the degree of acidity or alkalinity. A pH between 7.1 and 14 indicates an alkaline condition, a higher pH value indicating a greater alkalinity. A pH less than 7.0 indicates acidity and the lower the pH the greater the acidity. Most nutrients are readily available in soils with a pH range of 6 to 7, with a decrease in availability at soil pH above or below this range. Strongly acid soils have low extractable calcium and magnesium, a high solubility of aluminium, iron, and boron, and a low solubility of molybdenum. At the other extreme are alkaline soils. Calcium, magnesium and molybdenum are abundant in these soils with little or no toxic aluminium. Phosphorous availability may be greatly reduced at both very low and very high pH values due to phosphate fixation.
Organic Matter
Organic matter is derived from the residues of decaying organisms such as plants, animals, insects and microorganisms. Organic matter is a very important component of soil that stores and supplies plant nutrients, holds soil particles together, improves tilth and reduces the risk of erosion. Organic matter increases soil porosity and promotes water infiltration. To maintain organic matter, the rate of addition of crop residues must equal the rate of decomposition. Continuous production of row crops such as potatoes, beans or sugar beets usually results in a rapid decline of soil organic matter because the total amount of crop residue returned to the soil is low. The level of organic matter in the soil can be maintained by crop rotations that include perennial forage crops, by adding manure, or by the production of cereal crops where residues are not removed and minimum tillage is practiced.
Soil Compaction
Heavy equipment traffic and excessive tillage cause soil compaction. Soil compaction can be identified by the following symptoms:
- Excessive clod formation
- Slow water infiltration, especially in wheel tracks
- Distorted root and tuber growth and premature wilting from shallow rooting
Potatoes are sensitive to the physical condition of the soil. Dense or compacted soil interferes with root penetration as well as water and nutrient uptake. The plant will display symptoms of stress and the yield can be reduced. Compacted soil zones can be identified by carefully inspecting root growth patterns and soil texture in a 3-foot (0.9 m) deep trench.
Minimize compaction by reducing the amount of traffic or weight in the field. Avoid unnecessary vehicle traffic, tillage or hilling. The effect of compaction can be reduced by the use of tillage equipment that loosens soil to approximately 14 inches (35 cm) without inversion of soil layers. Subsoil tillage is expensive because of the high capital and operating costs of the equipment. A potato grower should confirm that compaction is causing production problems before investing in sub-soiling equipment.
Soil Drainage
Soil drainage refers to the ability of water to flow downward through soil. Well-drained soils have sufficient surface run-off and/or downward movement of water through the soil to result in relatively short periods of saturation. Poorly drained soils have a greater frequency and duration when the soils are saturated in all or part of the root zone. Soil drainage may be influenced by topography, uniformity of soil materials, proximity to the water table and climate.
Excessive water in the soil limits the free movement of the oxygen necessary for healthy root and tuber development. Excessive soil moisture increases the incidence of fungal diseases, and delays spring tillage, planting and harvesting. In extreme cases, excessive soil moisture causes tuber rot leading to the loss of the entire crop. Improved surface and sub-surface drainage can reduce the effect of excessive moisture conditions in imperfectly and poorly drained soils.
Stoniness
Soils that are free of stones or coarse fragments are most suitable for potato production. Factors such as size and abundance of stones must be considered when assessing a field for potato production. Large stones and boulders in a field make tillage difficult and can damage harvest equipment. Stones increase the chance of potato bruising during harvest. Stones cause a problem in seed production if they get into the cutter.
Written by P. Haluschak, C. McKenzie, K. Panchuk
The contents of this page are no longer available.
|
|
| |
|
|
| |
For more information about the content of this document, contact Shelley Barkley.
This information published to the web on January 12, 2005.
Last Reviewed/Revised on March 5, 2007.
|
|