Effects of Soil Characteristics

Table of contents

    Important tips for best management

    • Acidity, salinity and solonetzic soil problems can be major limiting factors in canola production. When severe, they affect soil characteristics and crop growth in ways that are very visible and easily determined, but at less limiting levels growth and yield may still be reduced without these obvious recognizable effects. This chapter discusses these and other soil characteristics and how to identify their extent, their effects on canola plants, and the steps to modify or reduce these limiting effects.
    • Crop residues are essential for the maintenance of tilth on solonetzic soils. Surface mulch and below ground residue (roots) are better for solonetzic soils than incorporating straw. Use tillage only as required for manure incorporation, for example, or for post-harvest heavy harrowing in cereal stubble to distribute residue.
    • Canola yields on acid soils with pH below 5.5 can be substantially increased by lime application.
    • Higher organic matter will improve canola yield potential on most soils. To improve soil organic matter, limit soil erosion, retain crop residue, apply adequate nutrients, and add manure.
    • Do not apply fertilizer or manure on frozen soils or snow, as spring runoff will remove many of those nutrients into rivers and lakes before they can enter the soil and be available to crops.
    • Match nutrient rates to crop uptake. Test manure for nitrogen and phosphorus content and apply at appropriate rates. Applying more nitrogen than a crop can use could increase potential for surface water and groundwater contamination. Nitrogen fertilizer products that slow the rate of fertilizer conversion to nitrate may also help reduce leaching losses.

     

    Soil texture

    Soil texture refers to the mix of sand, silt and clay in the soil. Sand particles are much larger than silt and clay particles, and soils high in sand have lower water holding capacities. Clay soils are denser with smaller particle sizes and air spaces, and have higher water holding capacities.

    Loam refers to a soil with a relatively equal mix of all three textures. Clay loam, for example, has all three, with more clay than sand or silt.

    The best soil for canola production tends to be Thick Black with lots of nitrogen mineralization potential and in a good rain area. Fine-textured soils hold more water and will  tend to produce better rainfall is low, assuming they start out with ample water in the soil profile.

    Solonetzic Soils

    There are about 6 million hectares (15 million acres) of solonetzic land in western Canada. This includes about 4 to 5 million ha (10 to 12 million acres) in Alberta; 1.5 million ha (4 million ac) in Saskatchewan, and 10,000 ha (25,000 ac) in Manitoba. [1]

    Solonetzic soils, often called burnout, blow-out or gumbo soils, are characterized by an impermeable, high sodium, clay hardpan from 5 to 30 cm (2” to 12") or more below the surface (top of Bnt horizon). This hardpan layer severely restricts root and water penetration below the topsoil. Solonetzic soils are formed on material that is naturally high in sodium salts or from materials that have been enriched with sodium salts through the upward movement of ground water.

    Aside from variations in depth of topsoil, these soils vary in the relative degree of formation of the hardpan. Some of these soils have a tough hardpan and are high in exchangeable sodium. Others have a hardpan that has been leached of sodium — which is not as tough and can be penetrated by some roots and moisture. The latter tend to be the more productive solonetzic soils. Most solonetzic soils in the Peace River region are of this type. [2]

    Solonetzic soils usually occur in association with normal soils. A field of good soil may contain patches of solonetzic soil. These patches may vary from 1 m (3') to several hundred metres (1,000') in diameter and may represent as little as 10% or as much as 90% of the soil in a particular field.

    Within a given field, good growth is often contrasted by thin, stunted growth on the solonetzic patches. Crops tend to develop an uneven or wavy appearance.

    Moisture is generally the most limiting factor to crop growth on solonetzic soils. The hardpan restricts root development and water infiltration and thus moisture use is limited mainly to the topsoil above the hardpan. Rainfall that doesn’t infiltrate flows to lower areas causing flooding. The deeper the depth of topsoil, the greater the moisture storage available.

    Solonetzic soils usually have a pH between 5.5 and 6.5 in the surface layers (A and upper B horizons), however, pH values may be 5.0 or lower. [3] Canola yields are reduced when the soil pH is 5.5 or lower.

    Seedbed preparation is relatively difficult on solonetzic soils with shallow topsoil as they dry out rapidly with cultivation. These soils are generally more suited to rangeland and pasture for this reason.  Growers who farm solonetzic soils are encouraged to direct seed using minimum tillage openers. [4]

    Solonetzic soils, if cultivated when wet, can form large, hard clods that are difficult to break down into a good seedbed. This condition inhibits moisture contact with the seed and results in poor germination. In addition, the surface soil structure tends to break down easily under rainfall, and dries to form a hard crust that restricts seedling emergence.

    Crop residues are essential for the maintenance of tilth on solonetzic soils.  Surface mulch and below ground residue (roots) are better for solonetzic soils than incorporating straw.  Use tillage only as required for manure incorporation, for example, or for post-harvest heavy harrowing in cereal stubble to distribute residue. [5]

    Provide surface drainage whenever possible to prevent temporary accumulation of water (ponding) before and after seeding. This will allow timelier seeding of the entire field and reduce uneven germination. Seed as soon as the soil temperature and moisture conditions are favourable for germination.

    Solonetzic soils, like most other soils, will respond to applications of commercial fertilizer. However, response to fertilizer may be limited by a lack of moisture. Therefore, the optimum rates of fertilizer applications tend to be lower for solonetzic soils compared to normal soils because of the lower yield potential. [2] Crops grown on solonetzic soils often suffer from drought in the middle to late growing season. Therefore, it is important that crops get an early vigorous start.

    Subsoiling (ripping) has increased production on some solonetzic soils for up to 5 years afterward due to deeper root penetration that improves soil water extraction and to increased water use efficiency.[6] However, not all solonetzic soils are suitable for subsoiling. Solonetzic layers that can be penetrated by roots and moisture may not benefit from subsoiling.[6]  Soil sampling to determine the suitablity of the soil for deep tillage and to identify the ideal depth of tillage is recommended.[2] Consult a qualified soils specialist before a soil is subsoiled.

     

    Soil pH

    Strongly acidic or alkali soils — pH below 5.5 or above 8.5 — will lower canola yield potential.[7] Soil pH is classified as follows:

    Less than 5.1

    Very strongly acid

    5.1 to 5.5

    Strongly acid

    5.6 to 6.0

    Moderately acid

    6.1 to 6.5

    Slightly acid

    6.6 to 7.5

    Neutral

    7.6 to 8.5

    Alkaline

    Greater than 8.5

    Alkali


    Most cultivated soils in western Canada are alkaline or neutral in reaction. However, large areas of soil with a pH of 6.0 or less occur naturally in Saskatchewan, Alberta, northeast British Columbia, and in Ontario. It has been estimated that medium to strongly acid soils (less than pH 6.0) occupy over 3 million hectares (7.4 million acres) in western Canada.

    Soil pH affects the structure, chemical, and biological properties of soils and, therefore, crop yields. On strongly acid soils with a pH of less than 5.5, canola yields are often reduced substantially.[7] Canola plant growth on acid soils can be limited by one or more factors, including:

    • toxicity of hydrogen ions, aluminum, iron, or manganese
    • deficiency of calcium, magnesium, potassium, phosphorus, boron, nitrogen, or molybdenum
    • reduced organic matter breakdown and nutrient cycling by microflora
    • reduced uptake by plant roots and inhibition of root growth. [8] 

    Acid soils often contain soluble forms of aluminum and manganese. As soil acidity drops below pH 5.5, soluble aluminum and manganese increase to toxic levels. Aluminum toxicity restricts root growth and phosphorus uptake and translocation within the plant. While the primary effect of aluminum toxicity is at the root level, the more visible foliar injury is due to nutrient deficiency, drought (due to poor root penetration) or pathogens, which are more pronounced on aluminum toxic, acid soils. Manganese toxicity causes chlorosis on leaf margins and cupping of leaves in canola. Aluminum and manganese often reduce the yields of crops grown on acid soils. [9] The graph below shows the general relationship between pH of mineral soil and the availability of various elements.

    How soil pH affects availability of elements

    Manitoba soil pH levels are outlined in this map: pH status of Manitoba Soils These numbers may be less that soil test numbers. This is becasue they are done with the saturaded paste method. Most commercial soil test labs use a 1:1 or 2:1 soil:water ratio method which produces a pH reading about 0.5 points greater than the saturated paste.

    Liming

    Research has shown that canola yields on acid soils with pH below 5.5 can be substantially increased by lime application. On slightly acid (pH 6.1 to 6.5) and moderately acid (pH 5.6 to 6.0) soils, liming will have a minor effect on canola yields (Figure 3). [10] [11] [12] [13]

    Figure 3

    A soil test is the only reliable way of determining whether soil is acid or not, and a lime requirement test should be used to determine the rate of lime to apply. Rates could be as high at 10 tonnes per hectare, depending on the soil type. (See Figure 4.) The pH increase is constricted to the top soil layer when the lime was incorporated. [14]

    Soil fertility benefit: The increase in soil pH resulting from lime application provides a more favourable environment for soil microbiological activity that increases the rate of release of plant nutrients, particularly nitrogen. Reduced soil acidity following liming also increases the availability of several other plant nutrients, notably phosphorus. A crop takes up only about 20% of fertilizer phosphorus in the application year. The remainder is fixed in the soil in various degrees of availability for succeeding crops. Below pH 6.0, the fixed phosphorus is retained in less available forms than on slightly acid and neutral soils (pH 6.1 to 7.5). Phosphorus availability is reduced because of the formation of relatively insoluble compounds through reactions of phosphorus with iron and aluminum. [15]  Therefore, one of the benefits of liming acid soils is the increased utilization of residual fertilizer phosphorus by crops. However, above pH 7.0, fertilizer phosphorus availability is reduced because of reactions with calcium and magnesium, so liming on these soils will not be beneficial.

    Soil texture benefit: Liming may improve the physical properties of some medium and fine-textured soils (particularly Grey and Dark Grey Wooded soils). Research at the Agriculture and Agri-Food Canada research centre in Beaverlodge, Alberta [13] showed that liming improved the stability of soil aggregates and, therefore, soil structure or tilth of Grey Wooded soils. Soils with a stable soil structure are less prone to crusting following intense precipitation, are well aerated, have a high rate of water infiltration and result in good germination and stand establishment of small-seeded crops like canola.

    Figure 4

    Aluminum and manganese benefit: On strongly acid (pH 5.1 to 5.5) and very strongly acid (pH less than 5.1) soils, liming reduces soluble aluminum and manganese to non-toxic levels and increases yield. In a three-year study (1993-95) at Beaverlodge, liming a pH 5.0 soil raised the pH to 6.5, increasing plant dry matter production and increasing canola yields by 37% in tilled and 17% in no-till soils.[13] The benefit of no-till systems is lower because these systems have been observed to accelerate soil acidification. [16] [17]

    The increased growth resulting from liming was likely due to a decrease in brown girdling root rot, reduced weed populations, increased pH-related changes in soil fertility, and likely other factors. Aluminum stress predisposes plants to infection by brown girdling root rot (Rhizoctonia solani Kuhn) due to reduced root vigour. In the Beaverlodge study from 1993-95, brown girdling root rot was observed in all plots of each treatment. Liming significantly reduced the severity of disease in the tilled soil, whereas under no-till the effect of lime on suppression of BGRR was not statistically significant. [13]

    Research shows that the benefits of a single application of lime can last for up to 30 years.[18] Liming is a substantial investment, although by-product liming materials from municipal and industrial facilities may provide an alternative low-cost liming material for farmers. It is important to identify the extent and severity of an acid soil problem. The most reliable method of identifying an acid soil problem is through soil tests. With careful sampling of fields, soil tests can determine the extent and severity of soil acidity, the rate of lime required and provide an estimate of crop response to lime.

    Wood ash vs. lime: Wood ash, the calcium carbonate-rich residue remaining from the combustion of bark, sawdust, and yard waste for energy generation for forestry product operations, is an effective liming material on acid agricultural soils.[14] Many of these forestry operations are in the northern Prairies, where a large percentage of highly acidic soils are located. Given the high cost of transporting agricultural lime to these regions, wood ash should be an appropriate and economic substitute for lime.[14] A 2002-05 study in the Peace River region compared yield results for wood ash, lime and untreated plots. Wood ash and lime were applied on an equivalent calcium carbonate basis. Canola yield (and barley and pea yields) were higher in treated versus untreated plots, and in most cases, canola yield was higher in wood ash treated plots compared to lime treated plots. This was probably due to the greater solubility of wood ash, and the greater amounts of nitrogen and phosphorus in wood ash compared to lime.[14] Wood ash also contains various other nutrients, including potassium, calcium, magnesium, manganese, copper, zinc, boron and molybdenum.

    Crops vary greatly in their tolerance to acidity. The numbers in the table represent the lowest pH these crops will tolerate.

    Table 1. Acidity Tolerance of Various Crops
    Crop pH
    Alfalfa, sugar beets 6.5
    Barley 6.0
    Canola, wheat, corn, red clover 5.5
    Potatoes, rye 5.0
    Oats 4.5

     

    Organic Matter

    Map of Organic Carbon Status of Manitoba soils

    Organic matter content of Alberta soils

    Organic matter is anything in the soil composition that is living or was once alive. It includes plant and animal remains, soil organisms, and substances produced by soil microbes. Organic matter is the material besides clay, silt and sand that gives rich soil its dark colour, sponginess and earthy smell.

    Organic matter is an essential component of soil because it:

    • holds soil particles together and stabilizes the soil, thus reducing the risk of erosion
    • aids crop growth by improving the soil's ability to store and transmit air and water
    • stores and supplies many nutrients needed for the growth of plants and soil organisms
    • prevents compaction, making it easier to work
    • retains carbon from the atmosphere
    • reduces the negative environmental effects of pesticides, heavy metals, and many other pollutants.[19]

    Over hundreds and thousands of years, soil biological and chemical components along with inorganic components contributed to the degradation and synthesis of complex soil organic matter and humic substances. Soil organic matter and humic substances contain at least 10 chemical classes of compounds such as proteins, lipids, carbohydrates and lignins.[20] 

    Soil test labs measure only the organic carbon component of soil organic matter, and then multiply by a factor of 1.72 to determine the organic matter reading provided with soil test results.[21] With this estimate, growers can then estimate, roughly, the pounds per acre of nitrogen, phosphorus and sulphur that organic matter will provide to a crop in a given year.

    Nitrogen:Mineralization of soil organic matter can generate 6 to 20 pounds of available nitrogen per acre for each percentage point of organic matter. For example, soil with 4% organic matter will supply 24 to 80 pounds of nitrogen through the growing season. Soil with 8% organic matter will supply 48 to 160 pounds of nitrogen per season. Warm conditions, ample moisture and high microbial activity increase the rate of mineralization. Mineralization can also increase with the number of years in min-till or direct seeding.

    Phosphorus:Each percentage point of organic matter provides up to 5 pounds per acre of phosphorus. For example, soil with 4% OM will provide up to 20 pounds of phosphorus through the season, and soil with 8% OM will provide up to 40 pounds.

    Sulphur:Each percentage point of organic matter provides 2-3 pounds per acre of available sulphur. For example, soil with 4% OM will provide 8-12 pounds of sulphur through the season, and soil with 8% will provide 16-24 pounds.

    Micronutrients: Soil OM complexes can also supply zinc, chromium, iron, and other inorganic elements to provide crops with many of the micronutrients required.

    Given the many benefits soil organic matter provides for a crop, growers do benefit from maintaining and increasing soil organic matter levels. Soil organic matter decreased dramatically across the Prairies in the decades after the plains were first broken for agriculture. Heavy tillage and summerfallow accelerated this decline, but in recent decades continuous cropping, conservation tillage and higher yielding crops have stopped and in many cases reversed this trend. [19]

    Soil organic matter can be compared to a bank account. To increase its size you need to ensure that additions to the account exceed the rate of spending. Practices to build the account include:

    • Limit erosion through minimum tillage and continuous cropping
    • Retain crop residue, especially roots in the soil and residue on the soil surface.
    • Increase yields by applying adequate nutrients. Higher yielding crops tend to have larger root systems and above ground biomass to build up organic matter.
    • Adequate nutrient rates also reduce or stop the mining of organic matter reserves, which will reduce OM over time.
    • Add animal manure, green manure, sewage sludge, wood chips, or peat. Soils amended with manure accumulated more organic matter than soils amended only with inorganic fertilizer. [22]


    In a long-term wheat yield study on the Prairies, the highest average grain yield was maintained in plots that lost the least amount of soil. When top soil is lost, which takes organic matter with it, soils lose their ability to produce top yields.[22] The long-term wheat study was at sites in Brown Chernozemic and Grey Luvisol soil types. In the study, the highest average grain yield occurred in fertilized continuous wheat plots in the Brown Chernozemic soil. Interestingly, those soils also received the lowest average annual precipitation (359 mm) compared to other sites in the study, showing that measures to conserve soil organic matter can provide a buffer against lower rainfall by improving moisture use efficiency.

    Not many studies have looked at the connection between organic matter levels and canola yields. In general, canola grown in Western Canada tends to yield best on high organic matter soils, especially when conditions permit a long growing season and with not too many high temperature days. [23]

     

    Soil Salinity

     All soils contain soluble salts — salts that dissolve in water. When the levels are sufficient to harm plants, the soils are "saline." Crops will vary in their tolerance to this salinity. Canola is considered moderately tolerant to salt and sodium, and can tolerate salinity up to levels of 5 to 6 dS/m.

    Saline soils are highly fertile and often very high in organic matter. That’s because the crop yields are very low in these areas, and nutrients have built up over years of blanket nutrient application. The ideal would be to map a field based on electrical conductivity (using Veris or EM38) and plug that into a variable rate applicator to automatically shut off fertilizer application to saline areas.

    Salinity is the result of excess groundwater moving downward and laterally through the soil dissolving and transporting soluble salts. Large areas in Canada's Prairie regions contain soil materials relatively high in soluble salts. The redistribution of these soluble salts by groundwater movement causes some areas to become excessively saline. When drainage is good, the salts are washed down through the soil and out of the root zone. When drainage is poor, as in low, flat or depressional areas, or in areas where roads or other construction interferes with normal drainage, the water table rises. When the water table rises to within 1 m (3') of the surface, water and salts can rise to the surface by capillary action. The water evaporates and the salts accumulate at the surface.

    Salinity also occurs in saline seeps on hill slopes, often part way up the slope on very long and high hills. Rainfall on the upslope part of the hill (recharge area) moves down through the soil, picking up salts on the way. The water not used by crops moves down until it reaches an impermeable layer, which impedes its progress. The water then flows laterally (seeps) until it reaches a position lower down the slope where the water table is closer to the surface. There, seep water causes the water table to rise allowing the salt laden water to move up to the soil surface by capillary action. The seep phenomenon can take place over relatively short distances within the same field or over distances of several miles. Salinity levels vary widely across a saline seep. Salinity also varies from spring to fall. Salinity usually appears on the soil surface just after spring thaw.

    The dominant salts in Prairie "saline seeps" are calcium (Ca), magnesium (Mg), and sodium (Na) cations and sulphate (SO4) anions. If Na levels are high or not balanced with the Ca and Mg, soil tilth can also be affected. The positively charged Na cations attach to the negatively charged clay particles in the soil, causing the soil to be sticky when wet and hard and impermeable when dry.

    Saline soils can be recognized by spotty growth of crops or by white crusts of salt, which accumulate on the soil surface usually in low-lying areas. Streaks of salt may be present in the soil even though white crusts may not appear on the surface. In many saline soils, it is not possible to see the salts and a laboratory soil analysis must be used to confirm their presence.

    Plants growing in saline areas may develop a blue-green tinge. Salt tolerant weeds such as Russian thistle, kochia, wild barley and goosefoot species are commonly found in areas of high salt concentration.

    The process of salt buildup is reduced when plants intercept the upward flow of saline groundwater and reduce the amount that reaches the soil surface. When plants are not present, almost all of the water loss takes place by evaporation at the soil surface. Summerfallow is a major contributor to salinity as it encourages a build-up of a water table. Water not used by crops accumulates in the subsoil eventually coming to the surface laden with salts. These salts interfere with seed germination and crop establishment.

    All irrigation water contains some salt. Over an extended period of irrigation where soil drainage is inadequate, salts accumulate in the soil and a salinity problem may develop. Water used in the major irrigation areas of Alberta and Saskatchewan is of high quality with little risk of salt buildup. Seepage or high water tables resulting from over irrigation cause most salinity under irrigation.

    Effects of Salinity on Canola Growth and Yield

    Some plant species tolerate high levels of salinity while others can tolerate little or no salinity. The relative growth of plants in the presence of salinity is called their salt tolerance. Salt tolerant plants avoid toxicity by the sequestration of the Na+ and Cl- ions into either vacuoles or roots by a salt exclusion mechanism[24]. Salt tolerances are usually given in terms of stage of plant growth over a range of electrical conductivity (EC) levels.

    The degree of salinity or total soluble salt concentration in a soil is routinely measured by soil testing laboratories with a conductivity test. Electrical conductivity (EC) is the ability of a solution to transmit an electrical current. The units of conductivity are usually given in deciSiemens per metre (dS/m). Table 2 categorizes salinity into general ranges from non-saline to very severely saline. These values are used for plant selection for saline soils.

    Table 2. Salinity Rating and Electrical Conductivity Value
    Soil Depth (cm)Non-SalineSlightly SalineModerately SalineSeverely SalineVery Severely Saline
    0 to 60 <2 dS/m* 2 to 4 dS/m 4 to 8 dS/m 8 to 16 dS/m >16 dS/m
    60 to 120 <4 dS/m 4 to 8 dS/m 8 to 16 dS/m 16 to 24 dS/m >24 dS/m
    * dS/m = deciSiemens per metre


    Excess soluble salts cause osmotic stress and ion toxicity in plant cells. Plants need both water and the nutrients dissolved in water for proper growth. The sap in plant roots contains salt that attracts water into the plant via osmotic pressure. Dissolved salts in the soil increase the osmotic pressure of the soil solution. This decreases the rate at which water from the soil will enter the roots. If the soil solution becomes too concentrated, plants will slowly dehydrate, lose turgor and starve, even though the supply of water and nutrients in the soil may be quite high. If the salt content of the soil water becomes too saturated, water may actually be withdrawn from the roots. Osmotic stress also results from desiccation and, therefore, is a common component of both drought and salt stress. High concentration of certain salts in the soil may also be toxic because some plants may absorb an excess amount of the salt, reducing growth or causing death.

    Canola is considered moderately tolerant to salt and sodium, and can tolerate moderate salinity up to levels of 5 to 6 dS/m. Canola is more sensitive to salinity during germination and emergence than later growth stages[25]. In a salinity study by the Agriculture and Agri-Food Canada in Swift Current, Saskatchewan, increasing levels of soil salinity reduced germination, emergence and emergence rate (Figure 5).[26] This greenhouse study showed that the per cent emergence and plant survival was not significantly affected until salinity exceeded 5.6 dS/m. Above this value, the number of days from seeding to initial emergence increased. With severe salinity, plants emerged rapidly, but over time the percentage that survived dropped off. (See figure 5 below)

    Figure 5

    Salinity under both moderate and severe conditions reduces average plant height, shoot and root biomass, number of leaves, leaf area, evapotranspiration, and crop yield at harvest. For example, the average harvest height in the above study averaged 167, 132 and 84 cm (66, 52 and 33"), respectively for the 0.6, 5.6 and 12.4 dS/m treatments. Root growth is also hindered at salinity above 6 dS/m. At 5.6 dS/m, canola yields in this study were reduced by 60% (Figure 6) and with severe salinity, canola yields were reduced by 80%. However, several other research studies have shown there was little effect on canola yields with salinity levels up to 10 dS/m.

    Figure 6

    Soil tests will show the extent of a salinity problem. Sample both affected and non-affected areas of the field. Perform analyses for electrical conductivity (EC), pH, cation base saturation, and calcium, magnesium, sodium and organic matter content.

    Another type of soil problem occurs when sodium levels are high in relation to calcium and magnesium in the soil. These soils are very sticky and slippery when wet, and are very hard, cloddy and prone to crusting when they dry. The sodium adsorption ratio (SAR) is the ratio of sodium to the beneficial soil structural cations, calcium and magnesium. When the SAR value exceeds 13, the soil is "sodic." If the SAR exceeds 13 and the EC is greater than 4, it is considered a "saline sodic" soil. Use a soil test to determine the SAR of soils.

    An Argentina study has shown that sodium, even with no soil crusting, can cause a slight reduction in canola emergence at SAR values of 20 and increase to a 60% reduction at SAR values above 34. At SAR values greater than 20, main stem growth and yield decreased slightly but an increase in the number of secondary branches compensated for this reduction. Reductions in number of stems, seeds per pod on the main stem, pods per stem and canola yields tend to decrease dramatically when SAR values exceed 34 (Figure 7). This may be partly due to induced calcium deficiency from excessive sodium.[27]

    Figure 7

    However, the most important effect of soil sodium is through increased crusting that reduces emergence. The amount of sodium required to affect emergence is much higher than that necessary for clay dispersion and crusting. The Argentina study showed SAR values of eight and even lower can encourage clay dispersion and crusting when raindrops impact the soil surface. Canola has a small seed size and at germination the cotyledons are pushed through the soil to the surface, making emergence more difficult in crusted soils. Crusting is also affected by soil particle size distribution as a high proportion of fine particles enhance soil susceptibility to crusting. Very fine seedbeds resulting from excessive tillage increase the susceptibility of a soil to form a crust. Crust strength will greatly influence emergence (Figure 8).

    Figure 8

    On soils with moderate salinity, use continuous cropping or at least lengthen the rotation to the maximum possible. Crops use the water rather than allowing it to move deeply into the soil or accumulate near the soil surface and contribute to salt movement.

    Use shallow tillage and maintain all possible crop residues at the soil surface. Deep tillage may, in many cases, simply bring more salts to the surface and make problems worse. Seed canola shallow and early so that seeds may germinate when surface salt levels are temporarily lowered.

    If soil salinity has already reached the stage where cereal and oilseed crops cannot be grown, consult qualified soil specialists on management procedures to combat and reclaim saline land. Salinity can be removed mechanically, but it requires irrigation on top and tile drains underneath to wash salinity out of the soil and drain it away.


    Environmental sensitivity

    Soil Texture and Water Quality

    Fertilizer runoff

    The two key nutrients for runoff risk are nitrogen and phosphorus. Nitrates and phosphates in water systems can promote the growth of aquatic plants and algae, which can reduce the aesthetic value of lakes and rivers and can reduce oxygen levels in the water, threatening fish numbers. When algal blooms die and decompose, oxygen in the water is depleted and fish and other aquatic organisms suffocate.[28]

    Nitrogen: The nitrate form of nitrogen — a form that plants take up — is very mobile and can leach through the root zone and get into ground water. Coarse textured (sandy) soils increase the risk of nitrate leaching to ground water, especially in depressional areas of the landscape and in regions with large amounts of precipitation.

    Phosphorus: On the relatively flat Canadian Prairies, phosphorus is more likely to enter waterways as dissolved phosphorus in surface-water runoff, and less likely through soil erosion of particulate phosphorus. Measures to reduce soil erosion, while providing other clear benefits, do very little to reduce phosphorus loading in Prairie lakes and rivers. Phosphate runoff is not generally regarded as a major issue on the Prairies, but this risk is substantial where tile drainage is used in areas where large amounts of phosphate have been or are being applied (e.g., tile drained, heavily manured soils that are sandy). The key management tool to prevent dissolved phosphorus runoff is to avoid manure and fertilizer application on frozen soils.[29]

    To limit fertilizer runoff:

    • Do not apply fertilizer or manure on frozen soils. When manure is applied on frozen soils or when nitrogen fertilizer is applied on snow, spring runoff will remove many of those nutrients before they can enter the soil and be available to crops. These nutrients end up in rivers and lakes.
    • Match nitrogen rates to crop uptake. Applying more nitrogen than a crop can use could increase surface water and groundwater contamination.
    • Nitrogen fertilizer products that slow the rate of fertilizer conversion to nitrate may also help reduce leaching losses.
    • Test manure for nitrogen and phosphorus contentand apply manure at rates that match crop use.


    Pesticide runoff

    Overland runoff and leaching of pesticides into water systems is more common in certain soil types.

    Sandy soil. Water moves through sandy soil quicker than through soils with higher clay content and smaller pores. Pesticide mixing and tank rinsing should be avoided on sandy soils, if possible.

    Clay soil. While clay soils may have lower rates of leaching, clay soils may result in higher rates of surface runoff losses. Clay soils are more prone to compaction and crusting, which limit infiltration and increase runoff.

    Further reading:

    Beneficial Management Practices: Environmental Manual for Crop Producers in Alberta

    Soil texture and water quality, Agriculture and Agri-Food Canada


    Soil health

    Soil health is a general term that can include good soil organic matter levels, granular soil structure, nutrient release and microbial activity.

    By following practices outlined in the first five sections of this chapter, growers can build soil organic matter, maintain soil nutrient levels, and keep salinity in check. These steps will contribute to overall soil health. Soil texture is more difficult to change, but growers do have management steps to reduce erosion and improve crop profitability that vary by texture.

    The key message with soil health is that growers can influence soil health. A soil’s ability to produce crops can be sustained over time, or degraded, or improved.


    References

    [1] The numbers come from soil inventory (soil survey) information. Maps and reports are available online here: http://sis.agr.gc.ca/cansis/  (**See Oyen East map to see how much solonetzic soil is in that region.**)

    [2] Lickacz, J. 1993. Management of Solonetzic Soils. Alberta Agriculture, Food & Rural Development publication Agdex 518-8.

    [3] Toogood, J.A. and Cairns, R.R. (co-editors). 1973.  Solonetzic soils technology and management.  Bulletin B-73-1. University of Alberta.

    [4] Ross McKenzie, research scientist, agronomy, Alberta Agriculture and Rural Development, personal communication, March 2012.

    [5] Rob Dunn, Agriculture Land Management Specialist, Alberta Agriculture and Rural Development, personal communication, March 2012.

    [6] M. C. J. Grevers, E. de Jong “Soil structure and crop yield over a 5-year period following subsoiling Solonetzic and Chernozemic soils in Saskatchewan,” Canadian Journal of Soil Science, 1993, 73(1): 81-91

    [7] Penney, D.C., Nyborg, M., Hoyt, P.B., Rice, W.A., Siemens, B. and Laverty, D.H. 1977. An assessment of the soil acidity problem in Alberta and northeastern British Columbia. Can. J. Soil Sci. 57:157-164. (Based on B. campestris rapeseed trials from early 70s)

    [8] Horst Marschner, “Mechanisms of adaptation of plants to acid soils,” Plant and Soil, Volume 134, Number 1 (1991), 1-20

    [9] Delhaize, E. and Ryan P.R. 1995. Aluminum toxicity and tolerance in plants. Plant Physiol. (1995) 107:315-321.

    [10] M. Nyborg and P.B. Hoyt, Effects of soil acidity and liming on mineralization of soil nitrogen,Canadian Journal of Soil Science, 1978, 58(3): 331-338

    [11] D. C. Edmeades, M. Judd and S. U. Sarathchandra , The effect of lime on nitrogen mineralization as measured by grass growth, Plant and Soil Volume 60, Number 2 (1981), 177-186

    [12] R.J. Haynes and R. Naidu Influence of lime, fertilizer and manure applications on soil organic matter content and soil physical conditions: a review Nutrient Cycling in Agroecosystems Volume 51, Number 2 (1998), 123-137

    [13] Arshad, M.A., Gill, K.S., Turkington, T.K. and Woods, D.L. 1997. Canola root rot and yield response to liming and tillage. Agron. J. 89:17-22. (http://pubs.aic.ca/doi/abs/10.4141/S04-023)

    [14] M. A. Arshad,* Y. K. Soon, R. H. Azooz, N. Z. Lupwayi, and S. X. Chang, Soil and Crop Response to Wood Ash and Lime Application in Acidic Soils, Agronomy Journal,2012, Vol 104 Issue 3, pp. 715-721

    [15] (Alberta Agriculture factsheet, Liming Acid Soils, http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3684

    [16] Dick, W.A., Organic Carbon, Nitrogen, and Phosphorus Concentrations and pH in Soil Profiles as Affected by Tillage Intensity, Soil Science Society of America Journal, 1983,Vol. 47 No. 1, p. 102-107

    [17] M.A. Arshad, M. Schnitzer, D.A. Angers, J.A. Ripmeester, Effects of till vs no-till on the quality of soil organic matter, Soil Biology and Biochemistry, Volume 22, Issue 5, 1990, Pages 595–599

    [18] Beckie, H.J. and Ukrainetz, H. 1995. Lime-amended acid soil has elevated pH 30 years later. Can. J. Soil Sci. 76:59-61

    [19] E.G. Gregorich, D.A. Angers, C.A. Campbell, M.R. Carter, C.F. Drury, B.H. Ellert, P.H. Groenevelt, D.A. Holmstrom, C.M. Monreal, H.W. Rees, R.P. Voroney, and T.J. Vyn, Chapter 5, Changes in Soil Organic Matter, “The Health of Our Soils: Toward sustainable agriculture in Canada,” Agriculture and Agri-Food Canada, 1995

    [20] Schnitzer and Monreal, 2011

    [21] ALS Labs, Saskatoon, personal communications with Dianne Kemppainnen

    [22] C. M. Monreal, R. P. Zentner, and J. A. Robertson, An analysis of soil organic matter dynamics in relation to management, erosion and yield of wheat in long-term crop rotation plots, Canadian Journal os Soil Science, 1997, p. 555-563

    [23] K. N. Harker, J. T. O’Donovan, T. K. Turkington, R. E. Blackshaw, N. Z. Lupwayi, E. G. Smith, H. Klein-Gebbinck, L. M. Dosdall, L. M. Hall, C. J. Willenborg, H. R. Kutcher, S. S. Malhi, C. L. Vera, Y. Gan, G. P. Lafond, W. E. May, C. A. Grant, and D. L. McLaren, High-yield no-till canola production on the Canadian prairies, Can. J. Plant Sci. (2012) 92: 221233

    [24] Ashraf, M. and McNeilly, T. 2004. Salinity tolerance in Brassica oilseeds.  Crit. Reviews in Plant Sci.  23:157-174

    [25] Steppuhn, H, Volkmar, K.M. and Miller, P.R.  2001.  Comparing canola, field pea, dry bean, and durum wheat crops grown in saline media.  Crop Science 41:1827-1833.

    [26] Steppuhn et al.

    [27] Carter, M.R., Webster, G.R. and Cairns, R.R. 1979.  Calcium deficiency in some Solonetzic soils of Alberta.  J. Soil Sci. 30:161-174

    [28] Alberta Agriculture and Rural Developoment, Managing Nitrogen to Protect Water Quality http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex928)

    [29] Don Flaten, University of Manitoba, personal communication, and Are Current Phosphorus Risk Indicators Useful to Predict the Quality of Surface Waters in Southern Manitoba, Canada? Esther Salvano and Don N. Flaten*  University of Manitoba, Alain N. Rousseau and Renaud Quilbe, Institut National de la Recherche Scientifique, Journal of Environmental Quality, 2009.