A field scale demonstration was used to compare yield response to applied fertilizer on three slope positions (low, mid, upper). The demonstration simulated how an air drill with variable rate application capability could change rates with changes in slope position.
The demonstration was located on W1/2 26-01-24-W2, southeast of Coronach, Saskatchewan on a Fife Lake clay loam soil. Under crop insurance the land is class J, Risk Area 03, with an area average wheat yield of 22.9 bu/ac on summerfallow and 15.1 bu/ac stubble.
Soil tests were done for the three slope positions on April 24 and May 8. Columbus spring wheat (70 lb/ac) was direct seeded in wheat stubble on June 1 with a Flexi-coil 5000 air drill equipped with 3 inch paired row openers on a 12 inch row spacing. Three rates of fertilizer (35-15-0) were used on low (44lb N/ac), mid (70 lb N/ac) and upper (60 lb N/ac) slope positions to achieve the yield goal of 35 bu wheat/ac. on all slope positions.
An altimeter was used to measure elevation along the slope. samples were taken for plant tissue analysis on July 30. An aerial infrared photograph was taken of the site in August.
The wheat was harvested and weighed on October 9. A combine
with a straight-cut header was used to harvest several strips,
the length of each treatment. Grain samples from each treatment
were taken to the local elevator for protein
determination.
Results
| Soil Test Nitrogen Levels - April 24 & May 8 | ||
|
Actual (lb/ac) |
Recommended (lb/ac) |
|
| Low |
20 |
45 |
| Mid |
16 |
65-75 |
| Upper |
19 |
60-70 |
| Plant Tissue Analysis - July 30 | ||||
|
Variable Rate |
Check |
|||
|
Tissue N (%) |
N Rate (lb/ac) |
Tissue N (%) |
N Rate (lb/ac) |
|
| Low |
2.15 |
44 |
1.70 |
28 |
| Mid |
2.47 |
70 |
1.72 |
28 |
| Upper |
2.41 |
60 |
1.96 |
28 |
| Grain Yield - October 9 | ||
|
Variable Rate |
Check |
|
|
bu/ac |
bu/ac |
|
| Low |
27.60 |
26.84 |
| Mid |
29.72 |
26.19 |
| Upper |
26.06 |
24.13 |
| Grain Protein (#1 CWRS) - October 11 | ||
|
Variable Rate |
Check |
|
|
% |
% |
|
| Low |
14.2 |
13.4 |
| Mid |
13.8 |
11.4 |
| Upper |
13.6 |
11.5 |
| Return on Variable Rate Fertilization | ||
|
Variable Rate |
Check |
|
|
$/ac |
$/ac |
|
| Low |
117.30* |
108.16* |
| Mid |
123.04* |
101.09 |
| Upper |
107.89* |
93.14 |
| * protein premium included | ||
| urea ammonium phosphate (35-15-0) $339/tonne | ||
Elevation - Field Profile
Upper - 2657 to 1665
ft
Mid - 2625 ft
Low - 2602 feet
| Precipitation (mm) Coronach Poplar River Power Station (10 miles west) | |||||||
| April | May | June | July | August | Sept. | Total | |
| 1996 | 27.9 | 36.2 | 84.8 | 44.8 | 11.8 | 32.5 | 238 |
| Normal | 25.6 | 51.2 | 66.2 | 42.2 | 36.0 | 29.1 | 250.3 |
Comments
At the Coronach site in 1996 there was a trend for grain yield and protein to decline as elevation rose. In contrast, plant tissue analysis revealed nitrogen content increased on the check and the treatment strip as elevation rose.
The net dollar return applying different rates of fertilizer on different slopes compared to a single uniform rate across the field was $2.21/acre, low-slope; $3.47/acre, mid-slope; and $0.12/acre, upper-slope.
Protein premiums improved the dollar return from variable rate fertilization. The greatest yield increase, 3.5 bushel - mid slope ($13.51), earned an extra $8.44/acre from higher grain protein.
At the rates of fertilizer used, nitrogen did not limit the crop yield potential. Lower rates of fertilizer may have improved net dollar return on the different slope positions. If this assumption were true and changes in elevation across the field may guide variable rate fertilization. Changes in elevation can be measured accurately in the field with a simple inexpensive altimeter.
Thanks to Cam Winter, project coordinator and Don Kirby, Coronach Conservation Cooperative for the time and effort they invested in this project. Thanks to Terry Kowalchuck, PFRA Soil Conservationist, for measuring field elevations. Thanks to Brian McConkey, SPARC, for project consultation and data analysis.
Funding for the project was provided by the Canada-Saskatchewan Agriculture Green Plan Agreement.