Soil N Monitoring, Fall 2012
Webinar October 19, 2012
Emerson Nafziger
Crop Sciences
University of Illinois
ednaf@illinois.edu
Percent of Total Uptake
Nitrogen Uptake In Corn
100
90
80
70
60
50
40
30
20
10
0
Leaves
Stalk, Tassel
Remobilization
Cob, Husks, Shank
Grain
40 Days
Stage:VE
0
V6
20
V12
40
V18 R1 R2 R3 R4 R5
60
80
Days After Emergence
Source: Adapted from How a Corn Plant Develops, Special Report 48 Iowa State University
100
R6
120
On-farm N rate trials, N. IL following a dry 2005 and winter of 05-06
Corn following Soy, 2006
250
250
200
200
Yield, bu/ac
Yield, bu/ac
Corn following Corn, 2006
150
100
150
100
50
50
0
0
0
50
100
150
200
Total N rate, lb/ac
250
0
50
100
150
200
Total N rate, lb/ac
250
N Left After Harvest?
• Warm March – mineralization started early and
kept going (until soil dried out)
• Normal N rates but short crop and less uptake
• Early death/early end of N uptake
• Rain after N uptake stopped mineralization
• Unused fertilizer N + unused mineralized N = ??
• NO3-N in tile water a concern
• Chance to carry over to 2013?
How much N remains?
Will it be there in Spring?
Should N rates be reduced?
Soil N, Urbana, 2012
400
Total N, lb/acre
350
300
250
200
Site 1
Site 2
Site 3
150
100
50
0
31-Aug
11-Sep
31-Aug
11-Sep
0 to 12"
12 to 24"
Sampling time and depth
Illinois Soil Nitrogen Monitoring
Fall 2012
• Identify 20 x 20 ft site after harvest:
– Following corn in 2012 (can take a few following soybean)
– Can choose different soils, yield levels
– Fields where corn will be grown in 2013 will allow
adjustments based on spring samples
• Collect samples after harvest and before NH3
application – last half of October, early November
• Need GPS coordinates (center of area)
– Accuracy at least .00001 degree; i.e., 40.23456°
– If degrees, minutes, and seconds, need to xx.xx”, for
example, 40° 14’ 4.42”
Illinois Soil Nitrogen Monitoring
Fall 2012
2
• If N was broadcast-applied in 2012, composite 4 to 6 probes
from random places in the area and mix in a bucket
• If N was banded (anhydrous or UAN) and soil hasn’t been
tilled:
– Take 2 cores in the band (separated by 5 ft or so down the row or in
separate rows), 2 cores ~8 inches away from the band, and 2 cores ~15
inches away from the band
– Composite the 6 cores as one sample, and mix in a bucket
• Take two samples: one 0 to 1 ft. deep and a second one (from
the same hole) 1 to 2 ft. deep. If the ground is too hard after
harvest to collect samples to 2 ft, take only a 0 to 1 ft. sample.
• If tillage occurs prior to sampling and the surface soil is fluffy,
step on the soil surface to firm it up, then sample in the
footprint.
Illinois Soil Nitrogen Monitoring
Fall 2012
3
• Take a generous cup of soil from the composited
sample in the bucket and place it in the sample bag
provided. Label bag with the site code (can use initials
and date, for example) and sampling depth
• Those not in the Growmark program request sampling
materials from me at ednaf@illinois.edu
• Need only:
– Your shipping address
– Number of sites you will sample or coordinate sampling
for
– Counties where sampling will be done
Illinois Soil Nitrogen Monitoring
Fall 2012
4
• I will forward the request to A&L Lab (copy to you) to send
you the requested number of sample bags (2 per site) and
forms and shipping boxes (with return service RS)
• Samples should be sent to A&L within 24 hours of taking
them (longer is OK if cool), or refrigerated if that is not
possible
– If you start to sample before supplies arrive, soil sample bags
and refrigerate samples
• You may get from A&L instructions to put several boxes
(sites) together for shipping
• Ship to A&L Monday through Thursday – not on Friday
Funding for this project is being provided by
the Council for Best Management Practices,
thus there will be no cost to producers and
those who take samples.
The thought is to make this an ongoing
project, with possible funding from the
revised fertilizer checkoff (NREC).
What Will the Numbers Tell Us?
• In the top foot of soil (4 million lb per acre), 1
ppm of NO3-N or NH4-N = 4 lb N/acre
• Fall soil N values can’t tell us how much we
will be able to adjust N rate for the 2013 corn
crop, but they will:
– Tell us the potential for loss if tile lines start
running in spring 2013
– Justify decreasing fall NH3 rates given the
expectation that some of this N may carry over:
We can’t adjust fall rates downward next spring if
there’s still N left…
What Happens to the Data?
• Soil N numbers (ppm NO3- and NH4+) will be
sent to the sample coordinators for
distribution to those whose fields were
sampled
• Values will be put on an Illinois map (no
names, hidden GPS values) to show how much
N there is
Fall 2012 NH3
• Need to wait until soils have cooled to <50°
• Use of nitrification inhibitor is suggested
• If soils are dry, need to take care (or delay) to get
proper sealing
– NH3 needs to dissolve in soil water and stay dissolved
– A lot of NH3 dissolves in a little water, but releasing NH3
gas into a dry soil means some will escape
– If soils continue to dry after application more will go out of
solution: can lose more over time
– Tillage before or after application can expose more soil to
drying
• Consider rate adjustments, especially if more N is
slated for spring (last rate adjustment) and there is (or
you suspect there is) soil N now
Soil N, Spring 2013
• The hope is that sites sampled in fall 2012 will be
sampled again in spring 2013, close to the time of
planting, but at least before last N application
– Will use same procedures as for fall 2012
– Have the ability to sample in fall-applied sites to see
form and amount remaining
• It’s normal for much fall NO3 to disappear by the
next spring, if tile lines run and/or it is wet when
soils are warm
• But the amount of soil N in fall 2012 appears to
be greater than normal, and most tiles are not
yet running, so there might be some N left for the
2013 (corn after corn) crop
What About N for the 2013 Crop?
• We like the MRTN
• For corn following soybean, N needs should be normal
– that is, subject to weather (N loss and crop growth)
– There is no evidence that low soybean yields in 2012
would mean higher N needs for the corn crop that follows
in 2013
• For corn following corn:
– Possibility of carryover N – will know in the spring
• MRTN minus lb soil N – adjustment?
– Less residue means less N tieup, so might mean slightly
less N needed
– As usual, much depends on spring conditions: moisture,
loss potential, soil warmup, crop growth, etc.
Nutrients in Corn Stalks
• Measurements of removal in 2010, leaving the
lower foot of stalk, per ton of dry residue:
– 15 lb N ($6.00 at $0.40/lb)
– 6 lb P2O5 ($3.00 at $0.50/lb)
– 20 lb K2O ($8.40 at $0.42/lb)
– Total value: $17.40 per ton of dry residue
• These are not “fixed”: N and (especially) K
leach out with weathering, and amounts will
decrease over time in the field