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Manage seedrow N risks

How much nitrogen (N) fertilizer can be put down with the seedrow? The question has been around as long as direct seeding and no-till. For many farmers, the amount of N required by the crop often exceeds what is generally recommended as safe, and they have turned towards side-banded or mid-row banding. But a significant group of farmers are still like to apply all the N in the seedrow.


December 1, 2008
By Bruce Barker

Topics

Westco research expands on the definitions of ‘favourable conditions’, refines seedrow N guidelines.

How much nitrogen (N) fertilizer can be put down with the seedrow? The
question has been around as long as direct seeding and no-till. For
many farmers, the amount of N required by the crop often exceeds what
is generally recommended as safe, and they have turned towards
side-banded or mid-row banding. But a significant group of farmers are
still like to apply all the N in the seedrow.

As a result,
gov-ernment extension and fertility researchers developed suggested
“safe” seedrow N guidelines.  However, these guidelines are based on
“favourable conditions” at the time of seeding. Favourable conditions
include excellent seedbed moisture, soils free of lime and salts,
uniform soil, good organic matter, seeding depth not excessive, and
good seed quality. “Over the past few years, farmers who have followed
the guidelines have experienced problems with seed and seedling damage
caused by N in the seedrow,” says Rigas Karamanos, manager, agronomy,
with Westco Fertilizers in Calgary, Alta. “Excessive amounts of
seedrow-applied nitrogen cause seed and seedling damage that can result
in a delay in crop maturity and reduced yields.” 

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Because the
guidelines are maximum rates of seedrow placed N as urea, Karamanos
says that it is commonly accepted that they should be significantly
reduced on soils that are low in organic matter or in soils that
contain free lime and/or salts in the surface layer. He says if the
seedbed is relatively dry, the maximum amount of seedrow urea-N must be
drastically reduced to avoid serious germination damage. “The problem
is that there isn’t a tool to change the rates. There hasn’t been a way
to determine how much less N should be applied in the seedrow under
adverse conditions,” says Karamanos. “Often farmers apply N rates far
greater than soil and weather conditions warrant, and end up with poor
plant stands and reduced yields.”

Research mined for data
To address this challenge, Karamanos went back into the Westco database
and looked at the factors affecting seedrow N. His objective was to
attempt to further refine existing N seedrow guidelines, expand them to
non-favourable conditions and develop a simple tool for the farmer to
assess the risk of applying N with the seed.

Karamanos
looked at 32 site years of experiments with CWRS wheat and 10 with
barley at 22 different locations across the Prairies over four years.
The data included three seedbed utilization rates, 10, 20 and 40
percent, and five N rates (0, 18, 36, 54 and 72 lbs. N per acre). In
all cases, phosphate was applied in the seedrow at a rate of 27 lbs.
P2O5 per acre.

The research measured relative plant stand compared to an unfertilized check, and final grain yield.

In wheat, Karamanos found three distinct responses to changing seedbed utilization (SBU) and N rates. 

Type
A essentially showed no impact of fertilizer N rate on the yield of
CWRS wheat at wide (40 percent) SBU, however, application of N at
narrow SBU (10 and 20 percent) resulted in grain yield decreases.
Relative plant stand was reduced with application of N in all cases;
however, at 40 percent SBU the reduction was within the limits that no
grain yield penalty was anticipated.

Type B found
there was no impact of fertilizer N rate on the yield of CWRS wheat at
narrow (10 percent) SBU; however, application of N at wide SBU (20 and
40 percent) resulted in grain yield increases up to a point. Relative
plan stand essentially remained unaffected at 40 percent SBU and low N
rates, whereas at higher N rates the relative stands of both wider and
narrow SBU were gradually reduced.

Type C resulted
in grain yield increases independently of SBU. Relative plant stand
remained unaffected at 40 percent SBU and declined at narrower SBU with
high N rates, however, again they remained within the limits that no
grain yield penalty is anticipated.

In barley, with fewer site years, Type A and Type C responses were observed.

After
identifying these three types of response, Karamanos identified common
characteristics for each type. There was a range of both soil texture
and soil organic matter (SOM) within each group. However, Karamanos
explains that each group was characterized by a distinct range in soil
test N levels as well as amounts of precipitation within 48 hours both
prior to and after seeding. “If the soil was dry, what mattered most
was the level of soil organic matter. If the soil was wet, what
mattered most was the soil test N level,” says Karamanos.

Within
SOM level groups, SBU and N rate could explain 63 to 83 percent of the
yield changes as a result of seedrow-placed N response for CWRS wheat.
Nitrogen rate was of least consequence under drier conditions, where
SOM appeared to play the most important roll; the reverse was the case
under moist to wet conditions.

Karamanos points out that
the guidelines for seedrow N application are strongly influenced by
soil moisture conditions at seeding and seedbed utilization, and are
subsequently modified by texture. Get rain just before or just after
seeding and seedrow N rates can go up.

And while soil
organic matter plays an important role in minimizing damage from
seedrow N application, its influence is much more predominant under
drier conditions.

Recommended rates of N application were
also influenced by the levels of residual soil NO3-N, and becomes
important under normal to very moist conditions as corresponding
recommended rates are influenced to a greater degree. However, under
dry conditions, the residual soil N level resulted in minimal influence
due to poor crop growth under dry conditions.

1 Values in this table are rounded off to the nearest 5 lbs./acre.

2 Underlined values represent Saskatchewan Agriculture and Food (2006) guidelines.

 

 chart1
Table 11. Comparison of the generally accepted guidelines for safe rates of fertilizer placed with the seed in western Canada (Saskatchewan Agriculture and Food 2006) and those derived from this study1.


Karamanos
subsequently developed a table comparing the generally accepted seedrow
N guidelines to those derived from his study. In some cases, the
refined seedrow N rates were lower, such as with Type A (dry soil, high
soil test N and little rainfall) on a light textured soil.  In other
cases they were higher, such as a Type C (moist, low-medium soil test N
and some rain near seeding) on heavy soils. “It is apparent that the
suggested guidelines are considered to be excessively restrictive by
many farmers. In fact, these guidelines are frequently exceeded by some
cereal growers who apply their total N requirement (40-70 lbs. N/acre)
in the seedrow with excellent results. However, the farmers who are
presently applying higher rates of seedrow N fertilizer have gained a
great deal of experience and expertise with this practice,” says
Karamanos. “The results from this study support their practice.”

Conversely,
the findings also support the experiences of farmers who have followed
the guidelines and still encountered stand establishment and yield
losses due to excessive
seedrow N damage.

New calculation tool developed
The
results from this detailed analysis of twenty seven experiments with
CWRS wheat and ten with barley allowed Karamanos to develop a tool that
a producer can use to minimize the risk from seedrow placed N with
wheat, barley canola, flax, oats and peas.  The Excel spreadsheet
requires the input of response Type anticipated based on soil moisture conditions, soil test N,SUB and SOM – the main parameters that Karamanos identified in his research analysis. 

The
tool has been enhanced with data from other work at Westco, as well as
data derived by the Canola Council of Canada to provide an estimate of
population stand under seedrow N rates in excess of those derived by
this tool. “The research and the development of the tool will help
farmers better modify their seedrow N applications to help prevent
stand establishment problems,” says Karamanos.