Soil N Monitoring, Fall 2012

Webinar October 19, 2012

Emerson NafzigerCrop Sciences

University of Illinoisednaf@illinois.edu

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Source: Adapted from How a Corn Plant Develops, Special Report 48 Iowa State University

Nitrogen Uptake In Corn

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Remobilization

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Corn following Corn, 2006

Total N rate, lb/ac

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Corn following Soy, 2006

Total N rate, lb/ac

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On-farm N rate trials, N. IL following a dry 2005 and winter of 05-06

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?

31-Aug 11-Sep 31-Aug 11-Sep0 to 12" 12 to 24"

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Soil N, Urbana, 2012

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Sampling time and depth

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Illinois Soil Nitrogen MonitoringFall 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 MonitoringFall 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 MonitoringFall 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 MonitoringFall 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