Soils, Cropping Practices and Fertilizer Use

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 Soils, cropping practices and fertilizer use | Cropping and soil management in the major soil groups | Problem soils

Soils, Cropping Practices and Fertilizer Use

Nitrogen and phosphorus
These two nutrients are most often responsible for limiting crop yields in Alberta. For crops grown on fallow, phosphorus may be the only nutrient limiting crop yield. Crop-fallow rotations rely heavily on nitrogen released from the mineralization of soil organic matter. As a result of frequent fallowing, soil organic matter levels can decline to a point where nitrogen fertilization is required to maintain yields of crops grown on fallow.

When the frequency of cropping is extended to crop-crop-fallow or approaches continuous cropping, nitrogen becomes an increasingly deficient nutrient. Therefore, when the frequency of cropping is increased, higher rates of nitrogen fertilizer, manure or frequent inclusion of legume crops in the rotation are required to maintain high crop yields. This greater need for nitrogen does not indicate that continuous cropping is more detrimental to the soil than crop-fallow rotations. The additional nitrogen required to maintain yields in continuous cropping systems helps to maintain soil organic matter.

Frequent fallowing of land:

  • depletes soil organic matter
  • exposes the soil to greater loss by wind and water erosion
  • contributes to increased salinity on some soils
From the standpoint of soil conservation, fallowing should only be practised when soil moisture reserves are inadequate for recropping.

Available phosphorus levels in Alberta soils are variable, but are usually in the moderately deficient range. Unlike nitrogen, phosphorus levels do not change quickly as a result of cropping, soil management practices or climate. Application rates of phosphorus fertilizer should reflect the available phosphorus status of individual fields, the requirements of the crop to be grown and the general growing conditions.

The level of available phosphorus in soils can be gradually increased by the application of moderate to high rates of phosphorus fertilizer and manure. Crop rotations that maintain or improve soil organic matter levels can also increase phosphorus availability. Topsoils contain much higher levels of available phosphorus than subsoils. Therefore, management practices that reduce wind and water erosion will help maintain soil phosphorus.

Potassium and sulphur
Deficiencies of potassium and sulphur are not as widespread as nitrogen and phosphorus deficiencies. But deficiencies of potassium and sulphur are common in particular areas and soil types. If crop yields are low and responses to nitrogen and phosphorus fertilizers appear small, attempts should be made to determine what other factors are limiting crop yields. Soil testing and field test strips are good methods of determining if potassium and sulphur are deficient.

Micronutrients are less commonly deficient that macronutrients such as nitrogen and phosphorus, but when deficiencies occur, the effects on crop yield and quality are as detrimental as with macronutrients. In Alberta, some micronutrients are rarely deficient while deficiencies of others, such as copper, are more common. Micronutrient deficiencies tend to be associated with particular soil types, growing conditions and crops such as:
  • manganese deficiency in oats under cold, wet soil conditions, boron deficiency in canola and alfalfa on a few Gray Wooded and sandy soils
  • copper deficiency on organic and mineral soils in central and northern Alberta
  • zinc deficiency, mainly on irrigated field beans in southern Alberta
The general use of micronutrient fertilizers is not recommended. Micronutrients should only be applied in situations where a specific deficiency has been identified.

Cropping and Soil Management in the Major Soil Groups

A wide range of soil types and climatic conditions exist within the province. Cropping practices and fertilizer use generally reflect the growing conditions in the major soil zones as shown on the soil zone map below.

Click here for a downloadable pdf file of the above map.

Brown soils
Brown soils occur in the semi-arid short grass prairie region of the province where the annual precipitation is about 30 cm. There are about five million acres of dryland cultivation and seven million acres of native range within the Brown soil zone. Dryland farming consists mainly of wheat-fallow rotations. Moisture limits crop production the most. Stubble cropping is not recommended unless there is greater than 75 cm of moist soil on medium-textured (loam) soils or 55 cm on fine textured (clay) soils. Minimum or conservation tillage is required to reduce wind erosion and conserve moisture.

Dark Brown soils
Dark Brown soils occur in the prairie region where the average annual precipitation is about 35 cm. There are about eight million acres of Dark Brown soils of which almost five million are cultivated. Cropping practices in this area are similar to those in the Brown soil zone, but improved moisture conditions allow:
  • a greater variety of crops
  • more frequent cropping of stubble
  • higher rates of fertilizer
Stubble cropping is not generally recommended unless there is greater than 68 cm of moist soil on medium- textured soils or 50 cm on fine-textured soils. Wind erosion and salinity control may necessitate stubble cropping when moisture levels are less than adequate. Conservation tillage practices are required.

Thin Black soils
Thin Black soils occur as a strip within the Black zone, adjacent to the Dark Brown soils. Soil moisture reserves and summer precipitation have a major influence on yields and fertilizer response. Precipitation is somewhat higher than in the Brown and Dark Brown soil zones. The southern portion of this zone receives more rainfall, but the rate of evaporation is higher than in the northern portion. Rainfall is quite variable in this area. Increased production can be realized from adjusting crop rotations and fertilizer rates to match soil moisture reserves. Soil moisture reserves may be increased with reduced tillage.

Black and Dark Gray Wooded soils of central Alberta
Moisture is less limiting to crop production in this area than in areas to the south and east. There is little need for fallowing to store soil moisture. Good yields can be obtained under continuous cereal cropping systems with adequate fertilization. Rotations that include grasses and legumes and the application of manure are recommended to help maintain soil organic matter and tilth. The higher rates of fertilizer recommended in Table 3 are suggested when previous experience has shown a good response to fertilizer and other management practices are geared to high yields. The relationship between fertilizer costs and crop prices should also provide economic returns that are high enough to offset the higher risk associated with high inputs.

Gray Wooded soils of central Alberta
Gray Wooded soils were developed under cool, humid conditions, and the surface layer is leached of clay and plant nutrients. Soil and organic matter is low and crusting often reduces seedling emergence. Crop rotations that include legumes and grasses help to increase soil organic matter, fertility and reduce crusting. Summerfallow and removal of cereal crop residues should be minimized. The application of manure is also very effective for increasing the productivity of Gray Wooded soils.

Moisture is not as limiting as elsewhere in Alberta, but the growing season is shorter. Nitrogen is often the major limiting factor to high crop yields on Gray Wooded soils.

Many Gray Wooded and some Dark Gray Wooded soils are deficient in sulphur. Legume crops will respond to the application of sulphur on one-half to three-quarters of these soils. Cereals and canola may also require additions of sulphur, particularly when nitrogen is added. The use of sulphur-containing fertilizers on cereals and canola is advised where a soil is known to show a sulphur response on legume crops, or a deficiency is indicated by a soil test.

Dark Gray and Gray Wooded soils of the Peace River region and northeastern Alberta
The agricultural soils in the Peace River region range from Black, developed under grassland, to Gray Wooded, which developed under forest vegetation. The Black and Dark Gray soils are relatively productive and respond to good management.

The Gray Wooded soils of this region are similar to those in central Alberta, but generally receive less growing season precipitation. Gray soils in the Peace region often have a high clay content and are particularly difficult to manage. Cultivation operations have to be timed according to soil moisture content. Poor soil moisture at seeding and soil crusting can reduce yields and fertilizer response. Soil-improving practices such as crop rotations with legumes or grass-legume mixtures, incorporation of crop residues and the addition of manure are helpful for improving the physical condition and reducing surface crusting. Because rainfall is often low during the early growing season, it is important to conserve moisture during seedbed preparation.

Irrigated soils
There are about one million acres of irrigated land within the irrigation districts in southern Alberta, plus some private irrigation systems scattered throughout the province. Soil fertility should be maintained at a level that is adequate to ensure an efficient, high level of productivity, which is required to offset the higher production costs associated with irrigation. Soil fertility can be maintained or increased through the use of commercial fertilizers, manure and legume crops.

In addition to maintaining fertility on irrigated soils, cropping practices that prevent the deterioration of soil structure and tilth should be used. Continuous production of row crops such as vegetables, sugarbeets and corn cause the rapid depletion of soil organic matter. The application of manure and crop rotations that include alfalfa, grasses and cereals will help maintain soil organic matter and tilth.

Crops grown in the Brown, Dark Brown and Thin Black soil zones in the irrigated areas of southern Alberta respond to nitrogen and phosphorus. Some irrigated soils have received relatively high applications of phosphate fertilizer for many years and may no longer respond to annual applications. These soils require only maintenance applications.

There have been a few instances of small responses to potassium, but this nutrient is not generally required.

Sulphur fertilization is not generally required on irrigated soils. There is normally a high level of sulphur in the subsoil, and approximately 10 lb/ac of sulphur is added to the soil with each 10 cm application of irrigation water.

Micronutrients are rarely needed on irrigated soils, because the content of micronutrients is sufficient to meet crop requirements. Only zinc deficiencies have been identified and confirmed on some irrigated field beans and occasionally on corn. Zinc, boron and copper deficiencies have been investigated on a number of other crops, but yield increases have either not occurred or have not been consistent.

The recommended rates of fertilizer for a crop vary because of soil type and past management practices. If the fertility of a soil has been built up through the use of manure, legume crops and adequate fertilization, one should use the lower rates of fertilizer in the recommended range. It is possible to get relatively good yields of a crop, such as cereals, for one year without the use of fertilizer where previous management has included the use of manure, legumes and fertilizer. Soil tests should be used to monitor soil nutrient levels.

Problem Soils

Solonetzic soils
Solonetzic soils are characterized by a hard-pan layer 5 to 25 cm from the surface. These soils occur in association with normal soils (see soil zone map) and often cause a typical uneven pattern of crop growth. This wavy growth pattern is particularly noticeable in years when moderate to severe moisture stress occurs because the rooting depth of the crop is restricted. Response to fertilizer on Solonetzic soils is also more variable than on associated normal soils because crop yields are decreased more by moisture stress. Therefore, the rate of nitrogen fertilizer should be reduced to 70 to 80 per cent of the rate used on normal soils. Banded applications of nitrogen are often more effective than broadcast applications on Solonetzic soils.

Acid soils
Soil acidity causes reduced yields of acid-sensitive crops such as alfalfa and barley on many fields in central and northern Alberta. Some 5 to 6 million acres are sufficiently acid to cause reduced yields of alfalfa, and 1 million acres are affected for growing barley.

Acid soils are readily identified by a soil test showing a low pH. The soil reaction is alkaline when the pH value is above 7, neutral at 7, and acid below 7. Crops vary greatly in their tolerance to acidity. Yields of alfalfa are reduced at pH 6 and less, and barley at 5.5 and less. Tolerance to acidity in decreasing order for annual crops is as follows: oats> flax>canola>wheat>barley.

Timothy, fescue, red clover and alsike clover are among the most tolerant forage crops, while alfalfa and sweet-clover are very sensitive.

Acid soils occur naturally and as a result of the long-term use of nitrogen fertilizers. The acidifying properties of nitrogen fertilizer are shown in Table 1. The extensive use of ammonium sulphate (21-0-0) is not recommended on acid soils because of its greater acidifying properties compared to other nitrogen fertilizers. Note, however, that some acid soils are deficient in sulphur, so the use of some ammonium sulphate or other sulphur-containing fertilizer may be required.

Table 1. Acidity of nitrogen fertilizers
Lime (CaCO3) neededto neutralize 1 lb of N
Ammonium sulphate (21-0-0-24S)
5.35 lb
Anhydrous ammonia (82-0-0)
1.80 lb
Urea (46-0-0)
1.80 lb
Ammonium nitrate (34-0-0)
1.80 lb

Liming is a common practice that is used to neutralize acidity caused by natural leaching and the use of nitrogen fertilizers. The productivity of moderately acid soils can also be improved by growing more acid tolerant crops, but the application of lime is the long-term solution to improving these soils.

Source: Agdex 541-2. Revised June 2004.

Other Documents in the Series

  Alberta Fertilizer Guide
Soils, Cropping Practices and Fertilizer Use - Current Document
Choosing the Kind and Rate of Fertilizer
Fertilizer Application and Placement
Soil Sampling and Testing
For more information about the content of this document, contact Duke.
This information published to the web on May 1, 2002.
Last Reviewed/Revised on June 1, 2004.