Don't Gamble with Fertilizer Rates!

 
 
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 Use risk analysis to minimize yield loss with seed-placed nitrogen.

It's clear from the growing body of research that direct-seeding cuts equipment investment and operating costs, and saves labour. The surge in direct-seeded acres in recent years is evidence that farmers agree.

Air seeders or air drills that can double-shoot or side-band are ideal one-pass systems. The risk of seed injury and yield reductions are minimized with a good seed to nitrogen (N) separation. One-pass systems that place seed and N together can also be used successfully, but the risks are higher.

The $64 question for farmers who want to seed-place N is: how do you determine safe rates?

It's a two-step risk analysis that weighs all the factors or conditions on your farm. The first step involves the factors row spacing, and the spread pattern of seed and N. The two factors are used to calculate Row Width Utilization, or RWU (sometimes also called Seed Bed Utilization -- SBU). It's a reading of the relative risk of emergence damage and yield reduction with seed-placed N.

To calculate the RWU, divide the width of seed and N spread by the row spacing and multiply by 100. For a more detailed explanation of RWU, see the box "How to Interpret RWU".

The traditional knife opener at left places fertilizer in a narrow band (3/4") with the seed. Fertilizer rates that are too high will burn the emerging seedling and adversely affect plant vigour, resulting in poor weed competition and delayed maturity. The sweep opener at right places fertilizer in a wide band (8") with the seed. Higher rates can be applied because seed-to-fertilizer contact is minimized by the wide spread.

PAMI research confirms that RWU is a good indicator of emergence damage and yield loss risk for wheat, barley and canola.

Rates of 0, 35, 70 and 105 lb (7.7, 15.4, 23.1 kg), respectively, of N as urea were placed with the seed on 8 in (203 mm) centres. Seed and N were spread 3/4 in (19 mm) with a knife, 2 in (50 mm) with a spoon, and 7 in (175 mm) with an 8 in (200 mm) sweep. The same rates were side-banded.

The RWU's for a 3/4 in (19 mm), 2 in (50 mm) and 7 in (175 mm) seed and N spread on an 8 in (200 mm) spacing, respectively, are: 9%, 25% and 88%. This suggests the knife presents the most risk to emergence damage and yield loss, and the sweep the least.


Clockwise, from top left: Spoon, Sweep, Knife, Swede Side Bander. PAMI applied rates of 0, 35, 70 and 105 lb (0, 7.7, 15.4, 23.1 kg), respectively, of N as urea with the seed on 8 inch centres. Seed and N were spread 3/4 in (19 mm) with a knife, 2 in (50 mm) with a spoon, and 7 in (175 mm) with an 8 in (200 mm) sweep. The same rates were side-banded. Preliminary results suggest the knife presents the most risk to emergence damage and yield loss, and the sweep the least.

Wheat and barley
Here's the preliminary results for the first year of a three-year research project on wheat and barley:

  • The knife caused emergence and yield to decrease as the N rate increased, except for wheat yields which increased as rates rose. The maximum safe seed-placed N rate for the knife appears to be about 35 lb/ac (39.2 kg/ha) for barley and possibly higher for wheat.
  • The spoon caused emergence to decrease at the highest N rate. However, yields were not reduced. This suggests the safe seed-placed N rate using a 2 in (50 mm) spoon is about 50 lb/ac (56 kg/ha) for wheat and barley.
  • The sweep and side-bander had the least impact on emergence, and yields were generally higher with higher N rates. This suggests safe rates of 70 lb/ac N (78.5 kg/ha) or possibly higher with the seed.
Canola
Here's the preliminary results for the first two years of research on canola:
  • In 1993 and 1994, as the rates of seed-placed N increased, emergence decreased, especially for the knife. However, yields were not drastically reduced as rates increased. Growers are warned that the delayed emergence and resulting uneven maturity caused by narrow spreads of seed and high rates of N can cause grade reductions and yield losses in short seasons. (See the graphs depicting three different application rates and their results on seedling emergence.)
What about other factors?
The second part of the risk analysis, to assess the impact of the other factors, is more difficult. For instance, what emphasis do you put on soil moisture, soil texture, fertilizer source, and crop type?

In PAMI's canola research, soil moisture played a key role in the safe seed-placed N rates. The drier the soils, the lower the emergence damage. But the opposite was found to be true for wheat and barley. This contradicts other research and traditional results. More work is required to verify this finding.

It's a gamble placing high rates of N with the seed. By using RWU and understanding all the other factors involved, farmers can minimize the risk to emergence damage and yield loss. Provincial crop specialists, PAMI specialists, and others can help farmers fine-tune seed-placed N rate decisions. In the meantime, PAMI is continuing its research to help farmers fine-tune the risk analysis for rates of seed-placed N.

The graphs illustrate the impact of three rates of nitrogen applied with four different openers. The message is clear -- openers that give the widest N spread pattern and the side-band opener present the least risk to emergence damage.

How N Affects Emergence

Effect of seed placed fertilizer on crop emergence 1994

Effect of seed placed fertilizer on crop emergence 1994

Effect of seed placed fertilizer on crop emergence 1994

How to interpret RWU
RWU is a formula that equates the spread pattern of seed and nitrogen (N) relative to row space. It's the amount of seedbed over which the N has been spread expressed as a percentage:

(spread / row) spacing x 100

RWU is a risk analysis tool to help determine the potential for emergence damage and crop reduction. The lower the RWU, the higher the risk of seed damage and crop loss.

For example, a 5 in (125 mm) seed and N spread (using a sweep) on a 10 in (250 mm) row spacing produces a 50% RWU [(5 / 10)x100]. This means seed and fertilizer are spread over half of the soil sub-surface area.

Switching to a 1 in (25 mm) seed and N spread (using a knife) on a 10 in (250 mm) row spacing will reduce the RWU to 10%. Since risk to yield losses rises as RWU falls, then it's clear a knife has five times the risk of crop loss.
Use RWU when purchasing equipment, when changing opener design, and when changing row widths.

Once RWU has been determined, examine the other factors that impact on how much seed-placed N can be used before making a rate decision. See "Seven Guidelines" for a look at the factors involved in determining safe seed-placed N rates.

A word about agronomic studies...
Farmers traditionally use yield as the measuring stick for successful crops, but emergence results can provide useful information early in the growing season.

Emergence results generally support yield results. However, unusual growing conditions can sometimes play with results, so it's important to make careful observations and recognize when growing conditions are above or below average.

Although the emergence results in this study don't support the yield results in every case (notably in wheat), we also know that the growing season in 1994 was unusually long - 140 frost free days in some areas. Such a long season allows late maturing treatments to recover from early seedling damage and perform as well as undamaged treatments.

These variations in growing conditions make it even more important to replicate studies in different areas and over a series of years. This report is based on only one year of data. The same study will be conducted again in 1995 and 1996. Averaging the results over several years will provide conclusive information. However, the initial emergence results from year one were so dramatic it is worthwhile to advise producers of the risks associated with over application.

Finally, we used the Swede Side Band opener as a performance target. This opener is designed for zero-till seeding. But producers are looking for one-pass seeding openers that perform equally well in minimum-till conditions, so the Swede Side Band opener provides a good target against which other openers can be measured.

Seven guidelines for safe seed-placed nitrogen applications this spring

  • Soil texture. The lighter the soil texture, the higher the risk to emergence damage and yield loss.
  • Seedbed moisture conditions at seeding. The lower the seedbed moisture, the higher the risk to emergence damage and yield loss. For dry soils, reduce the N rates shown in the cereal table by at least 50%. Canola may be an exception some years.
  • Fertilizer source. Ammonium nitrate (34-0-0) is less of a risk to emergence damage and yield loss then urea (46-0-0). For cereals, safe N rates can be increased by about 25% when using 34-0-0. For canola, the risk is identical for both forms of N.
  • Row space. The wider the row spacing, the higher the risk to emergence damage and yield loss. Row space and width of spread are used to calculate RWU.
  • Width of spread. The narrower the N spread pattern, the higher the risk of emergence damage and yield loss.
  • Crop type. Smaller seeded crops are more sensitive to emergence damage and yield loss to a given rate of N. Be cautious with high N rates placed with canola.
  • Application rate. The higher the N rate, the higher the risk to emergence damage and yield loss. Doubling the rate, for example, doubles the risks.
Consider the above factors, and then refer to the table on the back page of this report to help determine rates of N to be placed with cereal and canola seed.

Source: Saskatchewan Agriculture, Farm Facts Bulletin

The following are considered to be APPROXIMATE safe rates of urea (46-0-0) N applications with the seed of cereal grains if seedbed soil moisture is good to excellent (soil moisture at or near field capacity). All rates are in pounds actual N per acre (i.e. divide by 0.46 to get lbs. of 46-0-0 per acre). For cereals in dry soils, reduce N rates by at least 50%.

1 inch spread*
2 inch spread*
< 3 inch spread*
(disc or knife)**
(Spoon or hoe)
(Sweep)
Row spacing
Row spacing
Row spacing
6 in
9 in
12 in
6 in
9 in
12 in
6 in
9 in
12 in
RWU***
RWU***
RWU***
Soil Texture
17%
11%
8%
33%
22%
17%
50%
33%
25%
Cereal Grains
Light (sandy loam)
20
15
15
30
25
20
40
30
25
Medium (loam to clay loam)
30
25
20
40
35
30
50
40
35
Heavy (caly to heavy clay)
35
30
30
50
40
35
60
50
40
Canola & Flax
Light (sandy loam)
10
5
0
20
15
10
30
20
15
Medium (loam to clay loam)
15
10
5
30
20
15
40
30
20
Heavy (clay to heavy clay)
20
15
10
40
30
20
50
40
30
* 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.
** Some openers give less than 1 in spread.
*** See the box titled "How to Interpret RWU".

Source: Adapted from Farm Facts, produced by the Canada-Saskatchewan Agreement on Soil Conservation

Acknowledgements
The direct-seeding research for wheat and barley was carried out with funding from the Canada/Saskatchewan Green Plan in cooperation with the Naicam Crop Club, Foam Lake/Kelliher Crop Clubs, the Unity Group, and Saskatchewan Wheat Pool/Westco.

The direct-seeding research for canola was funded by the Saskatchewan Canola Development Commission.

The Alberta Farm Machinery Research Centre (AFMRC) is at the forefront of machinery evaluations, applied and scientific research, and development of innovative agricultural technologies.

 
 
 
 
For more information about the content of this document, contact Debbie Campbell.
This document is maintained by Nicole Huggins-Rawlins.
This information published to the web on February 19, 2002.
Last Reviewed/Revised on February 11, 2016.