Agronomy Library > Soil Conservation

Fertilizer Type Dictates Ground Opener Style
Author: Murray Green, Agricultural Engineer
Date Created: June 20, 2003
Last Reviewed: February 01, 2007

This title may be true, however, a better farm management approach to developing a direct seeding system would be to select the type of fertilizer that fits with the other issues which surround effective, profitable, and sustainable cropping on the farm.

Fertilizer types are essentially three: 
Anhydrous Ammonia NH3 It is a liquid under pressure in the tank, rapidly changing to vapor as it enters the soil.
2. Granular Urea 46-0-0 and blends with other dry granular forms.
3. Liquid Usually identified as 28-0-0 and again is blended with other liquid nutrients. It is only under the pressure that is needed to pump it through the liquid fertilizer system to the ground opener. 

Anhydrous Ammonia
Farmers select NH3 for the lower price, the higher field capacity at planting due to its concentration of 82-0-0, and the fact that it is delivered directly to the planter in the field.

It does, however, require an opener which ensures:
- the NH3 zone is separated from any of the seeds in the seed row. In most conditions, if the center of the ammonia tube outlet is 2 to 3 inches to the side, or to the side and below, the center line of the seed tube outlets, the soil buffer should be adequate. Equipment can be obtained from some fertilizer dealers that will display the actual location of the NH3 band relative to where the seeds are found.
- Seals the NH3 furrow to keep the ammonia vapor in the soil.
- Does not cause the opener to accumulate with frozen soil or cause the seed tube to plug.
- The best results with NH3 are with a separate double shoot knife opener or with a mid-row bander.

Granular Urea
In the case of a single shoot system the Urea is blended with the other nutrients, phosphorus, potassium, and sulfur as required. The limiting factor is the total amount of nitrogen being applied. Other factors determine when the nitrogen rate will be limiting. One factor that is affected by the choice of ground opener is the seed bed utilization (SBU). The wider the single shoot opener spreads the mix of seed and fertilizer the lower the potential for retarding or killing those enzymes on the seed coat that cause germination to begin.

When double shooting, it is important to keep the fertilizer granules away from the seeds, but not as far away as in the case of NH3. Most double shoot openers work well enough in loamy soils and those soils that are quite friable (works easily to form a good seed bed) as a result of good organic matter. However, in soils with a high percentage of clay, or in wet conditions, an opener that uses a deeper fertilizer banding point may not close the furrow, allowing seeds to fall into the fertilizer band. The number of seeds which encounter this fate are not great, but the undesirable result is much delayed emergence of these plants. Late plants, as with late tillers, result in immature heads and green kernels in the harvest sample. If in deed this is happening, it would be best if the fertilizer actually prevented germination of seeds which fall into the band. No plants from this zone is better than late ones. This occurrence of this problem will show up in your post planting survey.

Double shoot openers which band fertilizer between paired or single seed rows but at the same depth create more distinct bands of each. A paired row is pretty well impossible to fit under less than a 5 inch wide packer wheel. Reversing the flow and having a seed row in the center and a fertilizer out to the side or out both sides will fit under a narrower packer wheel. However, this will lose the proven benefits of fertilizer placed in a narrow band.

Liquid Fertilizer
Liquid nitrogen, (28 to 32 percent N) and blends containing other crop nutrients, has two distinct advantages:
- The nitrogen available to the crop is comprised of 53 to 58 percent ammonium nitrate which is derived from 34-0-0 fertilizer. The rest is nitrogen as ammonia (NH3) from urea (46-0-0). Ammonium nitrate is less toxic to the germinating seed and the developing seedling. The overall affect of the combination of these two nitrogen forms has less potential for damage to the plant stand. Canola is unusual in that it is affect as much by ammonium nitrate as by urea. Therefore "safe rates" of nitrogen for Canola is the same for all fertilizer types.
The liquid product, when dribbled from its small tube outlet, stays in a compact zone away from the seed. 

- Liquid fertilizer may be used in a variety of double shoot openers. The fertilizer itself would not cause a problem with seeds or plants, but the opener if equipped with a deeper penetrating fertilizer banding point, it could still cause unacceptable disturbance to the seed bed particularly in dry seeding conditions.

Success has been had by farmers who have installed liquid fertilizer outlets on 3 and 4 inch wide shovels or spread tips. The seeds tend to flow to the furrow edge, while the liquid fertilizer dribbles in a band along the center and at the same depth as the seed.