Nitrogen Ramp Calibration Strips in Manitoba
What
The Nitrogen Ramp Calibration Strip (NRCS) is a simplistic in-field method to determine nitrogen (N) supply of the soil and the N needs of the crop. It has been developed and explained by researchers at the Oklahoma State University (OSU)1,2. It resembles a research plot except it is non-replicated and non-randomized. The strip is fertilized with incrementally increasing rates of N before or shortly following seeding and visually inspected in mid-season to identify the N rate required for maximum biomass production and/or N sufficiency. The lowest N rate yielding the maximum mid-season forage production provides an assessment of grain yield and may even indicate the rate of additional N required to achieve optimum grain yield.
Why
The NRCS may be used for a variety of purposes:
- To quantify N replacement value of manure applications or legume contributions
- quantify losses of N due to excessive rainfall, etc
- To assess the appropriateness of current N fertilization strategies, including zone N management and N reductions due to economics
If near maximum yields can be achieved with mid-season N application, producers can use the in-season evaluation to determine appropriate mid-season application rates. In Manitoba this may apply to long-season crops (potatoes, corn) or to short-season crops where a base rate has been applied.
The NRCS is not a substitute for conventional N soil testing, but may compliment its use by helping quantify N losses or contributions from mineralization of organic N.
Where
The strip should be applied in an area representative of the majority of the field, similar to the site selection when using benchmark soil sampling. Soils maps, past crop production history (yield maps) and other images may be useful. The strip should be located off headlands. It is suggested by the OSU researchers that 2 strips be used per field in case response in one strip is confounded b y past practices, etc. Growers must be aware of the strip placement so they can turn off N in this area. Ways to manage this include programming the strip into a variable rate prescription or simply placing a 10’x 80’ tarp prior to broadcast application.
When
For N efficiency it is best to have the N applied prior to seeding, but application after crop emergence allows selection of an area with uniform crop stand. If application is delayed too long after emergence the N efficiency may not be as indicative of that applied at seeding.
Ideally the strip is applied in a non-N fertilized area. However, if N or manure has already been applied, the NRCS can indicate if that rate is sufficient or whether supplemental N may be warranted. One is unable to determine how much less N could have been used than the field rate used. If the NRCS is used to assess N replacement value, it should be placed in an area without the N source (manure, legume, etc).
How
The strip is laid out in a pattern some 10 feet (3 m) deep by 80 feet (24 m) long (depending on the number of N increments included). The plot is staked out with a tape measure and corners of individual 10’ x 10’ cells marked with flags or stakes (Figure 1).
Figure 1. Schematic layout of a nitrogen ramp calibration strip.
Hi N 180 N |
Check 0 N |
30 N |
60 N |
90 N |
120 N |
150 N |
180 N |
Pre-measured bags of urea fertilizer (Table 1) are then hand applied to each cell of 10 feet by 10 feet.
Table 1. Amount of urea-N required for individual NRCS cells.
Plot N rate Lb N/ac |
g urea/plot (10’x10’) |
g urea/plot (20’x20’) |
0 |
0 |
0 |
10 |
22 |
88 |
20 |
44 |
176 |
30 |
66 |
264 |
40 |
88 |
352 |
50 |
110 |
440 |
60 |
132 |
528 |
70 |
154 |
616 |
80 |
176 |
704 |
90 |
198 |
792 |
100 |
220 |
880 |
Urea should be treated with Agrotain to minimize losses to volatilization if rainfall is delayed. It is suggested that incremental N rates be in 10-30 lb/ac increments. In demonstrations we used 15 lb N/ac increments when strips followed manure or N applications and 20-30 lb/Ac increments when no base N rate was applied. Rates should climb to very high levels where N would not be limiting yield. Mark the individual cells so N rates are known.
With experience, it takes 15-20 minutes to measure, stake and apply N to each ramp strip.
The grower should continue normal pest management practices over the strip but avoid tramping lengthwise through the strip if possible.
Making the Mid-season N Assessment
Observations of early-mid season biomass and/or N sufficiency assessment is the critical step. Numerous methods can be used and are listed in Table 1.
Table 2. Criteria used to assess mid-season sufficiency of nitrogen supply.
Technique |
Sufficient |
Source |
Biomass |
Index to max |
|
Plant height |
Index to max |
|
Plant N concentration % |
Soil lab specifications |
|
SPAD Chlorophyll Index |
95-100% |
3 4 |
Leaf colour Plot colour |
Index to max |
5 |
Pre-sidedress soil nitrate test (lb N/ac 0-12”) |
>100 lb/ac for corn |
6
|
GreenSeeker NDVI |
Index to max |
7 |
Some measures do not have established reference levels, such as biomass and plant height, so they are indexed relative to the greatest measurement observed, with 90-95% generally considered sufficient. Those observations requiring lab analysis (soil N and leaf N content) may be considered too costly and perhaps only the promising rates are evaluated (in addition to 0 and Hi N).
In practice, the N sufficiency decision and final assessment is made in-season and no further observations are required. If the crop adviser desires, a harvest or end-of-season measure can be made, recognizing that yield measures may vary due to the non-randomized, non-replicated nature of the plot. Possible end-of –season measures are yield, grain protein, stalk nitrate in corn and residual soil nitrate-N (Table 3).
Table 3. Post harvest N sufficiency measures.
Technique |
Sufficient |
Source |
Grain yield |
Index to max. |
|
Post harvest residual nitrate-N (lb N/ac 0-24”) |
Not est. |
8 |
Stalk nitrate-N ppm |
750-2000 |
9 |
Grain protein content % |
>13.5 % CWRS wheat >11.5% w wheat |
10 4 |
Interpretation:
Experience with the various assessment tools is very important. In some cases the human eye can pick out the various green shades, but usually visual differences are too subtle to quantify and some of the above tools may be required.
- Contrast the High N check and the 0N check. If there are no discernable differences, the optimum N rate is 0.
- Move across the plot from low to high N rates. The minimum N rate that produces crop with 90-95% or greater biomass or N sufficiency is generally considered to provide optimal yield potential with the least N.
- Check the whole field N rate by matching it to a similar ramp
- Initial experience in Manitoba has shown this to be a useful educational, assessment and planning tool for growers and advisers.11
References
1 Edmonds D.E., M.C. Daft, W.R. Raun, J.B. Solie, and R.K. Taylor. 2008. Determining Mid-Season Nitrogen Rates with Ramp Calibration Strip Technology. Better Crops with Plant Food. Vol. 92. 2008 No.1 http://www.ipni.net/ppiweb/bcrops.nsf/$webindex/192E7FD695C7E135852573E9005646F4/$file/BC08-1p16.pdf
2 Raun, W.R., J.B. Solie, R.K. Taylor, D.B. Arnall, C.J. Mack and D.E. Edmonds. 2008. Ramp calibration strip technology for determining midseason nitrogen rates in corn and wheat. Agron.J. 100:1088-1093.
3 Brouder, S. and D. Mengel. 2003a. The pre-sidedress soil nitrate test for improving N management in corn. Agronomy Guide AY-314-W. Purdue University. http://www.agry.purdue.edu/ext/pubs/AY-314-W.pdf
4 Heard, J. and R. Gares. 2000. Nitrogen sufficiency in winter wheat for yield and protein based on soil, tissue and chlorophyll measurements. In Proceedings of 43rd Annual Manitoba Soil Science Society Meetings. Winnipeg. 2000. pp. 131-143.
5 Witt, C., J.M.C.A. Pasuquin, R. Mutters, and R.J. Buresh, 2005. New Leaf Color Chart for Effective Nitrogen Management in Rice. Better Crops/Vol. 89 (2005, No.1)
6 Brouder, S. and D. Mengel. 2003b. Determining nitrogen fertilizer sidedress application needs in corn using a chlorophyll meter. Agronomy Guide AY-317-W. Purdue University. https://www.agry.purdue.edu/ext/pubs/AY-317-W.pdf
7 Lafond, G. P., C. B, Holzapfel and W. E. May. 2007. Using the Greenseeker to Manage Nitrogen in Canola and Wheat. MB Agronomist Conference 2007. http://www.umanitoba.ca/faculties/afs/MAC_proceedings/proceedings/2007/Guy_Lafond.pdf
8 Heard, J. 2008. Can Manitoba growers fertilize for most economic yield and meet nitrate-N limits? MB Agronomist Conference 2008. https://umanitoba.ca/faculties/afs/agronomists_conf/media/Heard_soil_nitrate_poster.pdf
9 Heard, John.2009a. Validation of the Stalk Nitrate Test for Corn in Manitoba. Manitoba Society of Soil Science, 2009.
10Flaten, D.N. and G.J. Racz, 1997. Nitrogen fertility and protein in red spring wheat. In Proceedings of Manitoba Agri-Forum ’97. February 18, 1997. Winnipeg, MB pp.72-75.
11 Heard, J. 2009b. Field Validation of Nitrogen Ramp Calibration Strips in Manitoba. Manitoba Society of Soil Science, 2009.
John Heard
Soil Fertility Specialist, Chair MB Soil Fertility Advisory Committee
MB Agriculture, Food and Rural Development
Ph (204) 745-8093 Fax 745-5690
Box 1149, 65-3rd Ave NE
Carman, Manitoba R0G 0J0
