Choosing the Kind and Rate of Fertilizer

 
 
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 Nitrogen | Phosphorus | Potassium | Sulphur

The information needed to determine fertilizer requirements:

  • which nutrient or nutrients are deficient and the degree of deficiency
  • an estimate of crop response to a given level of fertilizer application
  • an assessment of economic returns from fertilizer
The more accurately these three factors can be determined, the greater the potential for profitable returns from fertilizer use. Methods of estimating nutrient requirements and crop response are discussed separately for each of the major nutrients (nitrogen, phosphorus, potassium and sulphur).

Nitrogen

Nitrogen fertilizer requirements for optimum economic returns on crops grown in Alberta cover a very wide range of application rates (Tables 2 and 3). For example, crops grown on fallow will often require little or no additional nitrogen, whereas non-legume crops grown on stubble land can give profitable returns to application rates of
100 lb per ac or more of nitrogen (N). The large range in nitrogen fertilizer requirements result from large differences in the amount of nitrogen supplied by the soil and the amount required by the crop. The yield potential of crops is a major factor affecting nitrogen fertilizer requirements.

Soil nitrogen
Non-legume crops obtain nitrogen from three main sources:
  • available nitrogen stored in the soil at planting
  • nitrogen released by the soil during the growing season (from soil organic matter, manure and crop residues)
  • fertilizer nitrogen
Except for crops grown on fallow, nitrogen stored in the soil, plus that released during the growing season, is normally insufficient to produce high yields. Because of our short growing season, only about one-quarter of the total nitrogen required for high yields of cereal and oilseed crops is supplied from nitrogen released from the soil during the growing season. Therefore, the amount of available nitrogen stored in the soil at planting has a major influence on the amount of nitrogen fertilizer required. A soil test is the most accurate way of determining the available nitrogen status of soils. If soil test results are not available, the cropping history of the field and past experience serve as useful guides.

Fallow fields are not normally considered to be deficient in nitrogen for cereal and oilseed crops, but a significant percentage of samples from fallow fields show a need for additional nitrogen. For example, recommendations based on soil tests indicate that 20 lb/ac or more of nitrogen are required on 30 to 40 per cent of fallow fields. However, the percentage of samples deficient in nitrogen varies widely from year to year.

Stubble fields not recently manured or broken from a legume will usually be low in available nitrogen and require high rates of nitrogen fertilizer to achieve high yields. Stubble fields recently broken from a legume will commonly have an intermediate level of available nitrogen. However, summaries of soil test results indicate large variations can occur from year to year. For example, stubble fields testing low in available nitrogen ranged from 25 to 85 per cent over a 10-year period.

Past experience, cropping history and general recommendations are useful guides to nitrogen fertilizer requirements, but the wide variation in available nitrogen that can occur from year to year provides a strong argument for the use of soil testing to help determine nitrogen fertilizer requirements.

Estimating crop response to nitrogen fertilizer
To assess economic returns from fertilizer, an estimate of the increase in yield from a given rate of application must be made. The following factors will influence crop response to applied nitrogen.

Available nitrogen - The nitrogen available in the soil at planting time is one of the main factors that influences crop response to nitrogen fertilizer. The nitrogen status of a field can be estimated from the previous cropping history, but is more accurately determined by a soil test.

Soil moisture reserves and growing season precipitation - These factors have a major influence on crop yields and the response to nitrogen fertilizer. In the Brown, Dark Brown and Thin Black soil zones, soil moisture reserves should be considered when choosing fertilizer rates. On medium-textured (loam) soils in the Brown and Dark Brown soil zones, moist soil to a depth of 75 cm and 68 cm respectively is considered adequate for cropping stubble land. On fine-textured (clay) soils in the Brown and Dark Brown soil zones, moist soil to a depth of 55 cm and 50 cm respectively is considered adequate for recropping. When soil moisture reserves exceed these levels, higher rates of nitrogen will usually give positive economic returns. If the entire rooting zone (90-120 cm) is moist, rates twice those normally recommended may be profitable.

Weed competition - Weeds lower the yield potential of a crop and compete for nitrogen fertilizer that has been applied. The higher rates of nitrogen recommended will usually not be profitable when weed competition is severe.

Delayed or late seeding - This factor usually decreases the yield response from nitrogen fertilizer. The yield potential of the crop is reduced, and the crop can make greater use of nitrogen released by the soil during the later part of the growing season. There is also greater risk of crop loss from frost and poor harvest conditions.

Crop variety - Varieties with higher yield potential will generally respond to higher rates of nitrogen application better than those with lower yield potential, providing that other factors are not limiting.

The economic returns from nitrogen fertilizer are easily calculated if a reliable estimate of crop response over a range of application rates can be made. Some soil testing laboratories provide predictions of the increase in yield from applied nitrogen based on the test for available nitrogen, soil type, location, the previous crop and crop to be grown. Farmers can then use these yield increase predictions in conjunction with their own past experience, current moisture reserves, fertilizer and crop prices, etc. to determine the rate of fertilizer to apply.

Phosphorus

Soil phosphorus
Unlike nitrogen, available phosphorus (P) levels tend to be characteristic of individual fields or soil types and do not vary widely from year to year owing to previous management. The rate of phosphorus required will depend on several aspects:
  • available phosphorus level of the field
  • phosphorus requirement of the crop to be grown
  • growing conditions
For non-irrigated crops, phosphorus fertilizer requirements are generally higher in central and northern Alberta than in southern Alberta. Cool, wet conditions early in the growing season enhance the response to phosphorus fertilizer. Also, phosphorus fertilizer often results in earlier and more uniform maturity, which is more important in central and northern regions where the growing season is shorter.

Crop response and rates of application
Phosphorus fertilizer requirements can be obtained from the general recommendation tables, but they are more accurately determined by a soil test or field test strips. As Figure 1 illustrates, crop response to phosphate fertilizer occurs over a narrower range of application rates than for nitrogen. Note that a response is obtained to the initial 10 to 15 lb/ac of phosphate even on soils testing moderately high in available phosphorus, and on soils testing low in phosphorus, most of the response is achieved at 40 to 50 lb/ac. Phosphate application rates therefore range between 10 and 50 lb/ac. In contrast, an economic response to nitrogen is seldom obtained on soils testing high in available nitrogen, but rates of 100 lb/ac or more may be profitable on soils testing low in available nitrogen.

Figure 1. Response comparison to nitrogen and phosphorous on barley.
Figure 1. Response comparison to nitrogen and phosphorous on barley.

Adjustments in the rate of application of phosphorus should be based on the same factors related to growing conditions and the fertilizer-crop price relationship as discussed for nitrogen. However, the adjustments should be proportionately smaller (e.g. a 20-30 lb/ac change in the rate of nitrogen warrants only a 10 lb/ac change in the rate of phosphate). On soils that require only maintenance applications of phosphate, the rate of phosphate application does not have to be changed as the rate of nitrogen is increased or decreased (N and P don't have to be applied at a constant ratio). A 10 to 15 lb/ac minimum rate of phosphate should be maintained except when the soil test is very high. On soils that are very deficient in phosphorus, such as eroded hilltops, a single plow-down application of 100 to 200 lb/ac may be beneficial in addition to normal annual applications.

Potassium

Potassium (K) deficient soils are not common throughout Alberta, but do occur quite frequently in certain areas and soil types. Potassium deficiencies tend to occur on sandy, calcareous soils and soils with poor subsurface drainage adjacent to and on organic soils. Soils that test low in available potassium occur most frequently in west-central, northwestern (excluding the Peace region) and northeastern Alberta.

Potassium is a relatively inexpensive fertilizer nutrient and is an important part of an efficient fertilizer program when K is deficient. Barley is somewhat more responsive to potassium than other cereal crops. Potatoes have a very high potassium requirement and therefore may require potassium fertilization on soils containing adequate amounts of potassium for other crops.

Increases in yield from potassium fertilizers are often less visible than for a nitrogen or phosphorus fertilizer. If potassium is tried on a test strip, yields should be measured carefully rather than visually estimated. A comparison of yield with and without potassium should be made where equal and adequate rates of nitrogen and phosphorus are applied.

Crop response to potassium chloride (0-0-60 or 0-0-62) has sometimes been observed on soils that are not deficient in potassium by soil tests. Preliminary research indicates these responses may be due to chloride. The application of chloride has been shown to reduce root and leaf diseases, but insufficient research has been conducted in Alberta to determine whether crop response can be predicted by a soil test. North and South Dakota use a soil test for chloride as a basis for recommending chloride fertilization. Soil testing laboratories in Alberta may use Dakota criteria as a general guide for chloride recommendations. Field trials should be conducted to establish whether or not the application of potassium chloride is beneficial on soils that are not deficient in potassium.

Sulphur

Some Gray Wooded and Dark Gray Wooded soils and well drained Black soils are deficient in sulphur. Sulphur deficiency is not common on Brown and Dark Brown soils. Deficiencies seldom occur in crops grown on fallow, but legume crops, cereal and oilseed crops that have been well-fertilized with nitrogen fertilizer commonly require sulphur fertilization. Sulphur requirements of canola and legumes are greater than those of cereals.
The need for sulphur fertilizer can be determined by a soil test. If a test strip is used to determine responses, the comparison with and without sulphur should be made using equal and adequate rates of nitrogen and phosphorus throughout. Sulphur fertilization is inexpensive owing to the relatively low rate of application required (10-30 lb/ac). Supplying adequate sulphur when it is deficient will usually provide very high returns.

Table 2
General fertilizer recommendations for Brown b soil in Alberta ( in pounds of nutrient per acre) a
Crop
Previous Crop
Nitrogen
(N)
Phosphate
(P2O5)
Application and Placement c
Spring Wheat fallow
5 - 20
10 - 20
Phosphate - place in the seed row or band with nitrogen in fall or spring. Under cool, wet conditions and on low phosphorus soils, placing some phosphate (10-15 lb/ac P2O5 with the seed is usually beneficial.Nitrogen - the relative effectiveness of fall and spring broadcast and band applications.
the maximum rates that can be safely placed in the seed row.
stubble
20 - 50
0 - 15
Malting Barleyfallow
-
-
stubble
-
-
Oats and
feed barley
fallow
5 - 20
10 - 20
stubble
20 - 55
0 - 15
.
Fall rye fallow
0 - 30
20 - 25
Phosphate - place in the seed row or band before seeding.
Nitrogen - broadcast early the following spring
stubble
20 - 50
15 - 20
Winter Wheat fallow
20 - 30
10 - 25
stubble
25 - 55
10 - 25
.
Flax fallow
-
-
Phosphate - band or place in the seed rows.
Nitrogen - very sensitive to fertilizer placed in the seed row, N should be banded or broadcast
stubble
-
-
.
Canola and Mustard fallow
5 - 15
10 - 20
Phosphate - a maximum of 25 lb/ac can be placed in the seed row. Band higher rates.
Nitrogen - rates higher than 10 lb/ac must be broadcast or banded.
stubble
20 - 55
10 -15
.
Grassfallow
-
-
Broadcast after seed harvest in fall or early spring depending on species.
Broadcast fertilizer in late fall or early spring.
stubble (with less than 20% legume)
-
-
.
Grass - Legume 20-40% legume
-
-
Broadcast fertilizer in the late fall or early spring.
40-60% legume
-
-
.
Legume (greater then 60%)
-
-
A large single application of phosphate (100-200 lb/ac) may be beneficial on low P soils.
.
Potatoes
fallow
-
-
Fertilizer should be banded 3 to 5 cm away from seed row.
stubble
-
-


Table 2 (cont)
General fertilizer recommendations for Dark Brown b soil in Alberta (Rate in pounds of nutrient per acre) a
Crop
Previous Crop
Nitrogen
(N)
Phosphate
(P2O5)
Application and Placement c
Spring Wheat fallow
5 - 20
15 - 35
Phosphate - place in the seed row or band with nitrogen in fall or spring. Under cool, wet conditions and on low phosphorus soils, placing some phosphate (10-15 lb/ac P2O5 with the seed is usually beneficial.
Nitrogen - the relative effectiveness of fall and spring broadcast and band applications.
the maximum rates that can be safely placed in the seed row.
stubble
25 - 60
0 - 25
Malting Barleyfallow
5 - 15
15 - 35
stubble
25 - 50
0 - 25
Oats and
feed barley
fallow
5 - 15
15 - 35
stubble
35 - 65
0 - 25
.
Fall rye fallow
25 - 35
20 - 30
Phosphate - place in the seed row or band before seeding.
Nitrogen - broadcast early the following spring
stubble
30 - 55
15 - 25
Winter Wheat fallow
25 - 35
20 - 40
stubble
30 - 65
15 - 30
.
Flax fallow
5 - 10
10 - 20
Phosphate - band or place in the seed rows.
Nitrogen - very sensitive to fertilizer placed in the seed row, N should be banded or broadcast
stubble
20 - 30
0 - 15
.
Canola and Mustard fallow
5 - 30
15 - 20
Phosphate - a maximum of 25 lb/ac can be placed in the seed row. Band higher rates.
Nitrogen - rates higher than 10 lb/ac must be broadcast or banded.
stubble
35 - 70
15 - 20
.
Grassfallow
30 - 60
0 - 15
Broadcast after seed harvest in fall or early spring depending on species.
Broadcast fertilizer in late fall or early spring.
stubble (with less than 20% legume)
40 - 90
0 - 15
.
Grass - Legume 20-40% legume
30 - 65
0 - 20
Broadcast fertilizer in the late fall or early spring.
40-60% legume
10 - 30
0 - 35
.
Legume (greater then 60%)
0 - 10
0 - 35
A large single application of phosphate (100-200 lb/ac) may be beneficial on low P soils.
.

Potatoes
fallow
-
-
Fertilizer should be banded 3 to 5 cm away from seed row.
stubble
-
-
    Table 2 (cont)
    General fertilizer recommendations for Thin Black soil in Alberta (Rate in pounds of nutrient per acre) a
    Crop
    Previous Crop
    Nitrogen
    (N)
    Phosphate
    (P2O5)
    Application and Placement c
    Spring Wheat fallow
    5 - 25
    15 - 35
    Phosphate - place in the seed row or band with nitrogen in fall or spring. Under cool, wet conditions and on low phosphorus soils, placing some phosphate (10-15 lb/ac P2O5 with the seed is usually beneficial.
    Nitrogen - the relative effectiveness of fall and spring broadcast and band applications.
    the maximum rates that can be safely placed in the seed row.
    stubble
    35 - 65
    10 - 35
    Malting Barleyfallow
    5 - 25
    15 - 35
    stubble
    35 - 65
    10 - 35
    Oats and
    feed barley
    fallow
    5 - 30
    15 - 35
    stubble
    35 - 80
    15 - 35
    .
    Fall rye fallow
    25 - 35
    20 - 35
    Phosphate - place in the seed row or band before seeding. Nitrogen - broadcast early the following spring
    stubble
    30 - 60
    15 - 30
    Winter Wheat fallow
    25 - 45
    25 - 45
    stubble
    40 - 80
    20 - 40
    .
    Flax fallow
    5 - 10
    15 - 20
    Phosphate - band or place in the seed rows.
    Nitrogen - very sensitive to fertilizer placed in the seed row, N should be banded or broadcast
    stubble
    20 - 45
    0 - 20
    .
    Canola and Mustard fallow
    5 - 35
    15 - 25
    Phosphate - a maximum of 25 lb/ac can be placed in the seed row. Band higher rates.
    Nitrogen - rates higher than 10 lb/ac must be broadcast or banded.
    stubble
    30 - 70
    0 - 30
    .
    Grassfallow
    30 - 70
    0 - 30
    Broadcast after seed harvest in fall or early spring depending on species.
    Broadcast fertilizer in late fall or early spring.
    stubble (with less than 20% legume)
    60 - 110
    0 - 30
    .
    Grass - Legume 20-40% legume
    40 - 80
    0 - 35
    Broadcast fertilizer in the late fall or early spring.
    40-60% legume
    10 - 30
    0 - 45
    .
    Legume (greater then 60%)
    0 - 10
    0 - 50
    A large single application of phosphate (100-200 lb/ac) may be beneficial on low P soils.
    .
    .
    .
    .
    Potatoes
    fallow
    -
    -
    Fertilizer should be banded 3 to 5 cm away from seed row.
    stubble
    -
    -
      Table 2 (cont)
      General fertilizer recommendations for Black and Gray Wooded b soil in Alberta (Rate in pounds of nutrient per acre) a
      Crop
      Previous Crop
      Nitrogen
      (N)
      Phosphate
      (P2O5 )
      Potassium
      (K2O)
      Sulphur
      (S)
      Application and Placement c
      Spring Wheat fallow
      5 - 35
      15 - 40
      .
      .
      Phosphate - place in the seed row or band with nitrogen in fall or spring. Under cool, wet conditions and on low phosphorus soils, placing some phosphate (10-15 lb/ac P2O5 with the seed is usually beneficial.
      Nitrogen - the relative effectiveness of fall and spring broadcast and band applications.
      - the maximum rates that can be safely placed in the seed row.
      stubble
      30 - 80
      15 - 40
      .
      .
      Malting Barleyfallow
      5 - 35
      15 - 40
      .
      .
      stubble
      30 - 80
      15 - 40
      .
      .
      Oats and
      feed barley
      fallow
      5 - 40
      15 - 40
      .
      .
      stubble
      40 - 100
      15 - 45
      .
      .
      .
      Fall rye fallow
      5 - 20
      20 - 35
      .
      .
      Phosphate - place in the seed row or band before seeding.
      Nitrogen - broadcast early the following spring
      stubble
      35 - 70
      20 - 35
      .
      .
      Winter Wheat fallow
      -
      -
      .
      .
      stubble
      -
      -
      .
      .
      .
      Flax fallow
      5 - 10
      15 - 20
      .
      .
      Phosphate - band or place in the seed rows.
      Nitrogen - very sensitive to fertilizer placed in the seed row, N should be banded or broadcast
      stubble
      20 - 45
      15 - 20
      .
      .
      Canola and Mustard fallow
      5 - 45
      15 - 35
      -
      0 - 10
      Phosphate - a maximum of 25 lb/ac can be placed in the seed row. Band higher rates.
      Nitrogen - rates higher than 10 lb/ac must be broadcast or banded.
      stubble
      40 - 100
      15 - 35
      -
      0 - 20
      .
      Grassfallow
      45 - 90
      0 - 40
      -
      0 - 10
      Broadcast after seed harvest in fall or early spring depending on species.
      Broadcast fertilizer in late fall or early spring.
      stubble (with less than 20% legume)
      60 - 120
      0 - 40
      -
      0 - 10
      .
      Grass - Legume 20-40% legume
      45 - 90
      0 - 35
      -
      0 - 30
      Broadcast fertilizer in the late fall or early spring.
      40-60% legume
      10 - 30
      0 - 50
      -
      0 - 30
      .
      Legume (greater then 60%)
      0 - 10
      0 - 60
      -
      0 - 30
      A large single application of phosphate (100-200 lb/ac) may be beneficial on low P soils.
      .
      Potatoes fallow
      25 - 50
      45 - 90
      30 - 60
      0
      Fertilizer should be banded 3 to 5 cm away from seed row.
      stubble
      70 - 110
      55 - 110
      50 - 100
      0
      a Residual response to the higher rates may persist for two years, particularly when the year of application is dry and production is low. Therefore annual application may not always be necessary
      bSee comments regarding soil moisture reserves and their importance in determining crop rotations and choosing fertilizer rates under Cropping and soil management in the major soil groups and Choosing the Kind and Rate of Fertilizer
      cSee : Fertilizer application and placement

      Note:
      i) Table 2 should be used in conjunction with the discussion in the text of the publication. Soil tests will provide additional and important information for choosing fertilizer rates.
      ii)Blanks - indicate that the crop is not grown or recommended in that soil zone.
      iii)See Table 7 for converting from pounds of nutrient to pounds of fertilizer.

      Table 3
      General fertilizer recommendations for irrigated crops (pounds of nutrient per acre)
      Crop
      Nitrogen
      Phosphorus
      Potassium
      Application and placement a
      Wheat - hard red spring
      35-110
      20-50
      0
      Broadcast or band N in fall or early spring. Place phosphate in the seed row or band with N at seeding.
      - utility & durum
      35-110
      20-50
      0
      - soft white spring
      35-130
      20-50
      0
      Broadcast-incorporated P2O5 application should be 2 times the recommended rate at low P soil test levels.
      - winter
      35-80
      (spring applied)
      20-50
      0
      Barley - feed
      40-130
      20-50
      0
      - malting
      35-130
      35-50
      0
      - silage
      50-130
      35-50
      0
      Oats..
      35-80
      20-50
      0
      Fall Rye.
      30-70
      20-50
      0
      Triticale .
      35-90
      20-50
      0
      Canola and
      Mustard
      .
      35-140
      35-110
      35-60
      20-50
      0
      Band or broadcast and incorporate both N and P2O5 . Maximum amount of P2O5 with seed is 20 lb/ac.
      Potatoes
      90-170b
      0
      Broadcast or band N. Sideband P2O5 at seeding.
      Sugar beets
      0-140b
      30-65
      0
      Broadcast in fall or early spring. Drill in P2O5 (side band) at seeding
      Corn- sweet
      70-120b
      35-60
      0
      Sideband P2O5 at seeding. Side dress nitrogen.
      Broadcast or band N. Sideband P2O5 at seeding.
      - silage
      80-150
      45-60
      0
      - grain
      80-150
      30-60
      0
      Peas
      0-40
      30-40
      0
      Broadcast or band N. Maximum amount of P2O5 with the seed is 25 lb/ac.
      Beans
      10-40c
      30-40
      0
      Broadcast or band N in fall or early spring.Sideband P2O5 at seeding.
      Lentils
      10-30c
      20-40
      0
      Sunflowers
      70-135
      20-60
      0
      Flax
      20-100
      15-40
      0
      Broadcast or band N in fall or early spring. Drill in maximum 15 Ib/ac P2O5 with seed.
      Alfalfa
      0-20c
      30-60
      0
      Broadcast in early spring.
      Grass- for hay
      90-150
      0-60
      0
      Broadcast 50 to 100 Ib/ac N in early spring, follow with 50 Ib/ac N in mid-July for maximum production.
      - for pasture
      110-200
      0-60
      0
      Grass - Legume- legume
      (20%-40%)
      45-90
      30-60
      0
      Broadcast fertilizer in early spring. Additional nitrogen (50 Ib/ac) may be required in mid-summer to maintain peak production.
      Broadcast fertilizer in early spring.
      - legume
      (40%-60%)
      10-35
      30-60
      0
      Legumes
      (greater than 60%)
      0-10
      30-60
      0

      Remarks: See Soils, Cropping Practices and Fertilizer Use - Irrigated soils.

      aPhosphorus is most effective when drilled with or near the seed. Broadcast-incorporated applications should be twice to four times the drilled-in rate to beequally effective at low P soil test levels. Banded phosphorus will be similar to or intermediate between drilled-in and broadcast applications See phosphorus placement.
      bNitrogen requirements on coarse-textured soils (sandy loam and loamy sand) are usually higher than on fine-textured soils (loam, clay loam and clay).
      cFertilizer application rates are based on inoculation with specific rhizobia bacteria to obtain nitrogen fixation.
       
       
       
       

      Other Documents in the Series

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