August 2006

Guidelines for Safely Applying Fertilizer with Seed

Granular nitrogen - cereal grains

The table below illustrates APPROXIMATE rates of urea (46-0-0) N that can be safely applied with cereal grain seed if seedbed soil moisture is good to excellent (moisture at or near field capacity)

All rates are in pounds actual N per acre (divide by 0.46 to get pounds of 46-0-0 per acre)

¹ Width of spread varies with air flow, soil type, moisture level, amount of trash and other soil conditions, so it must be checked under field conditions.
² Some openers give less than 1 in. spread. Urea should not be applied with the seed on light soils when a double disk drill is being used.
³SBU (Seedbed Utilization) is the amount of the seedbed over which the fertilizer has been spread. Thus, it is a reflection of the relative concentration of fertilizer. SBU (%) is the width of spread divided by the row spacing multiplied by 100. For example, if the seeding implement has a 6 in. spacing and spreads the seed and fertilizer over 2 in., the SBU would be 33 percent (2÷6x100=33). The higher the SBU, the more fertilizer that can safely be applied with the seed. Although some openers spread the seed and fertilizer vertically, SBU does not take this into account since it is generally recommended that all seed be placed at an even depth for even germination and emergence.

• Cereal grains are treated as a group. Oat is slightly more tolerant of seed placed N than barley which is slightly more tolerant than wheat.
• Ammonium nitrate (34-0-0) is less damaging to seed than urea (46-0-0). For cereal grain only, suggested N rates can usually be safely increased by about 20 lb./acre when ammonium nitrate is used. This recommendation should be approached with caution where seedbeds are dry. Ammonium toxicity is the major cause of germination and seedling damage when urea is the N source. With ammonium nitrate, which has a higher salt index than urea, excess salinity in the seed row is the major cause of germination and seedling damage. This salt effect is more severe under dry conditions.
• With canola, ammonium nitrate and ammonium sulphate are just as damaging to seedlings as urea.
• N rates in the table are in addition to the N in safe rates of seed placed phosphorus fertilizer (monoammonium phosphate).
• Soil Moisture Considerations:

Seedbed moisture can rapidly decline after seeding depending on the opener used, packing, residue cover and weather. Practices that conserve moisture in the seedbed are encouraged.

Where seedbed moisture is low or when the weather is hot and windy, reduce the rates shown in the tables by approximately 50 percent.

Granular nitrogen - canola

The table below illustrates the APPROXIMATE rates of urea (46-0-0) N that can be safely applied with canola seed if seedbed soil moisture is good to excellent (soil moisture at or near field capacity)

All rates are in pounds actual N per acre (divide by 0.46 to get pounds of 46-0-0 per acre)

¹ Width of spread varies with air flow, soil type, moisture level, amount of trash and other soil conditions, so it must be checked under field conditions.
² Some openers give less than 1 in. spread.
³SBU (Seedbed Utilization) is the amount of the seedbed over which the fertilizer has been spread. Thus, it is a reflection of the relative concentration of fertilizer. SBU (%) is the width of spread divided by the row spacing multiplied by 100. For example, if the seeding implement has a 6 in. spacing and spreads the seed and fertilizer over 2 in., the SBU would be 33 percent (2÷6x100=33). The higher the SBU, the more fertilizer that can safely be applied with the seed. Although some openers spread the seed and fertilizer vertically, SBU does not take this into account since it is generally recommended that all seed be placed at an even depth for even germination and emergence.
 

• N rates in the table are in addition to the N of seed-placed phosphorus fertilizer (monoammonium phosphate).
• For canola, ammonium nitrate is as damaging to seedlings as urea.
• Use the same soil moisture considerations outlined for cereal grains.

Anhydrous ammonia

Anhydrous ammonia cannot be placed with seed, however, in recent years equipment has been modified to allow anhydrous ammonia to be placed at seeding time in a band or other arrangement, separated from the seed. The anhydrous ammonia must be separated from the seed by at least 2 to 3 in. and be placed below and to the side of the seed, or to the side of the seed. It should not be applied directly below or above the seed. The anhydrous ammonia reaction zone with the soil is pear-shaped. The anhydrous ammonia tends to follow the furrow upward, so attempts at placing it beneath the seed will likely lead to seed damage.

Liquid nitrogen

In liquid nitrogen (28-0-0) half of the nitrogen is in the form of urea and the other half is in the form of ammonium nitrate. Safe rates of seed-placed N as liquid nitrogen are only slightly higher than for urea. (See the tables for the urea values.)

Depending on the seeding equipment, a producer may be able to safely increase N application beyond the urea guidelines by adjusting the tubes so that liquid fertilizer and seed are separated by soil. Safe rates will depend on the amount of separation, soil, moisture and other agronomic considerations discussed in other sections of this bulletin. Safe rates must be determined by the producer on a by-case basis.

Phosphorus

The main phosphorus fertilizer used in Western Canada is monoammonium phosphate (NH₄H₂PO₄) with various analyses such as 12-51-0 and 12-52-0. Monoammonium phosphate has a low salt index and does not release much ammonium, so it has a relatively low toxicity to seedlings.

Maximum safe rates of actual seed-placed phosphate (P₂0₅) fertilizer (divide by 0.51 to get pounds of 12-51-0 per acre)

Other agronomic considerations:

• Field variability in rolling land can affect results. Eroded knolls often have soils that are low in organic matter. These areas may show greater seedling damage from seed-placed fertilizer.
• Seeding too deep places more stress on seedlings and increases the likelihood of damage from seed-placed fertilizer.
• Cold soil temperatures, disease, poor-quality seed or high-herbicide residue can delay emergence or weaken the seedling, thereby increasing the probability of fertilizer damage.
• Every effort should be made to ensure good seed-to-soil contact when seed-placing fertilizer, especially N.

For more information contact your MAFRI office.

Acknowledgements

The following guidelines were approved by the Manitoba Soil Fertility Advisory Subcommittee. Recommendations were adapted from "Revised Guidelines for Safe Rates of Fertilizer Applied with the Seed," written by Les Henry (University of Saskatchewan), John Harapiak (Westco Fertilizers), Harry Ukrainetz (Agriculture and Agri-Food Canada - retired) and Brandon Green (Saskatchewan Agriculture, Food and Rural Initiatives).