Red River Valley Site-Specific Nitrogen Management Experiences in 1996

Allan Cattanach - Sugarbeet Specialist, NDSU/U of MN., Fargo, ND
Dave Franzen - Extension Soil Specialist, NDSU, Fargo, ND
Dan Bernhardson - Agriculturist, American Crystal Sugar Co., Moorhead, MN
Dave Braaten - Agriculturist, American Crystal Sugar Co., Moorhead, MN

Recent development in new technologies have given growers the potential to increase accuracy of nitrogen management and sugarbeet profitability. About 25 percent of all sugarbeet acreage in Minnesota and North Dakota was grid sampled and variable rate fertilized in 1996. Past experiences have indicated about 70 percent of the fields grid sampled are likely to give profitable responses to variable rate fertilization. Experience in 1995-1996 has shown about 30 percent of those fields are not likely to give profitable responses to variable rate fertilization.

Objective(s):

The purpose of these studies was to compare yield, quality and profitability of sugarbeet production using site-specific versus conventional soil sampling and fertilizer application techniques. An additional objective was to determine if nitrogen recommendations could be further refined by increasing or decreasing nitrogen application rates based on individual grid organic matter levels.

Procedures:

Two studies were established in grower fields at Felton and Foxhome, Minnesota. Fields were grid sampled on about a 4.4 acre grid size to determine nitrogen status at both locations and organic matter content at Felton. Headlands were not included in the studies. The conventional sampling consisted of about 30 probes in a random pattern across the field. Twelve 4.4 acre grids were sampled at each location. Six or eight soil samples per grid were taken. Soil samples were taken from 0-6", 6-24", and 24-48" depths at Felton. Samples at Foxhome were taken only from the 0-6" and 6-24" depths. Soil analysis was performed on Foxhome samples at Agvise laboratories and by Minnesota Valley Testing Labs for Felton samples.

At Felton 12 grids across a field were grid sampled then split into thirds (a) one-third grided and variable rate fertilization; (b) one-third grided and variable rate fertilized with organic matter adjustment; and (c) one-third conventionally fertilized.

Based on soil tests the Foxhome site was fertilized to a level of 150 lb/A available soil test plus residual nitrate-nitrogen. The Felton site was fertilized to a level of 120 lb/A available nitrate-nitrogen with adjustments made when 2-4' nitrogen is more or less than the 30 lb/A level. The studies were designed only to look at variable rate nitrogen application.

The field at Felton had very uniform plant populations of about 160 beets/100' of row. Plant population at Foxhome was about 150 beets/100' of row on the conventional strips as sampled by North Dakota State University scientists and 120 beets/100' of row for grid sampled and fertilized. This plant population difference probably skewed North Dakota State University sample results.

At each location North Dakota State University/University of Minnesota scientists took six ten foot long hand dug samples per grid for yield, quality, and plant population data. A total of 144 samples were taken at Foxhome and 216 samples taken at Felton. Harvest was completed the same day in the first week of October that the grower harvested the field strips at Foxhome. Harvest was completed by North Dakota State University/University of Minnesota scientists at Felton on September 30 and grower harvest completed on October 14. Quality analysis on all samples was done at the American Crystal Sugar Co. lab at East Grand Forks, Minnesota. All grower loads were delivered to the same outlying piling ground at Foxhome to reduce chances for errors.

Results and Discussion

Grid sampling gave a far more accurate estimation of total nitrogen in the 0-4' soil profile at Felton than conventional sampling, Table 1. The field conventional soil test level was 62 lb/A, 0-4'. Table 2 shows levels of available nitrate-nitrogen at Foxhome.

Nitrogen recommendations by grid for Felton is shown in Table 3 and for Foxhome in Table 4. Wide variations in amounts of fertilizer nitrogen applied per grid occurred based on soil sampling method. Nitrogen applied based on organic matter adjustment ranged from 0 to 120 lbs/A. Nitrogen applied range from 14 to 108 lbs/A based on normal grid sampling while the conventional nitrogen application was 80 lbs/A. At Foxhome, nitrogen fertilization based on grid sampling varied from 58 to 106 lbs/A versus a 97 lb/A nitrogen rate based on conventional sampling. However, only 3 of 12 grids varied more than 15 lbs/A from the conventional fertilization rate. Percent of fields over or under fertilized based on soil sampling method are shown in Table 5.

The effects of grid sampling and variable rate spreading on sugarbeet yield and quality compared to the conventional method for Felton from the University data is shown in Table 6. The soilection grid sampling increased gross return by $36.00 per acre over conventional soil sampling. The organic matter fertilization adjustment increased gross return per acre by $31.00. A baseline organic matter content of four percent was used for this field and soil type. Nitrogen fertilization was increased by 3.0 lb/A for each 0.1 percent decrease in organic matter below 4.0 percent. Conversely nitrogen fertilization was decreased 3 lb/A for each 0.1 percent increase in organic matter above the four percent baseline.

The cooperating grower at Felton harvested each of the six treatment grids as an individual grower contract. The grower harvest resulted in $54.00/A more gross return from variable rate fertilization adjusted by organic matter content, Table 7. Standard variable rate fertilization by Soilection increased gross return by only $13.00/A compared to conventional methods.

The effects of grid sampling (0-2' deep only) and variable rate nitrogen application at Foxhome, MN. is shown in Table 8. North Dakota State University and University of Minnesota researchers data showed a major reduction of nearly 1600 lbs/A recoverable sugar and $244.00 lower return per acre from grid sampling and variable rate fertilization. They also observed a consistent reduction in plant population of 30 plants/100' of row in the variable rate fertilized grids. Not knowing the residual nitrate-nitrogen content in the 2-4' depth soil profile may contribute to these large unexpected differences. In contract to the university findings the grower results determined an increase of 207 and 111 lbs. recoverable sugar per acre from the variable rate fertilized grids, Table 9. Increased value of the recoverable sugar per acre was $38.00/A and $16.00/A, respectively.

Summary

I. Concerns with North Dakota State University/University of Minnesota and grower data at Foxhome, MN. include:

1. Soil sampling was done only 0-2 ft.
   
2. The average plant population varied widely from conventional to grid blocks. Why? There was not obvious explanation.
   
3. Fertilizing to 150 lb/A versus lower levels of available soil residual nitrate-nitrogen plus added fertilizer nitrogen may reduce benefit of grid sampling.

II. Conclusions/Foxhome, 1966

1. The average amount overfertilized by conventional methods at Foxhome was only 14 lb/A.
   
2. The average amount underfertilized by conventional methods at Foxhome was only 9 lb/A.
   
3. Field variability may have been too low in the 0-2' depth too expect a response to variable rate fertilization.
   
4. Unknown levels of nitrogen from 2-4' in depth may have contributed to lack of benefit from grid sampling and variable rate fertilization as determined by the university yield sampling.
   
5. Standard grid layout in a field does not always best reflect the nitrogen status of a field.

III. Conclusion/Felton, 1996

1. The average amount overfertilized by conventional methods versus grid sampling and variable rate fertilization at Felton was 33 lb/A (with a range of 5 to 66).
2. The average amount underfertilized by the conventional methods versus grid sampling and variable rate fertilization at Felton was 18 lbs/A (with a range of 10 to 24).
3. The average amount overfertilized by conventional methods versus grid sampling and variable rate fertilization plus OM adjustment was 47 lbs/A (with a range of 1 to 80).
4. The average amount underfertilized by conventional methods versus grid sampling and variable rate fertilization plus OM (organic matter) adjustment was 27 lb/A (with a range of 4 to 40).
5. A greater range of residual nitrate nitrogen variability made response to variable rate fertilization more likely at Felton than Foxhome.
6. With grid sampling OM adjustment produced more recoverable sugar per acre than conventional methods in 9 of 12 grids (with a range of 61 to 1021 lbs. and a mean of 344 lbs).
7. With grid sampling OM adjustment produced less recoverable sugar per acre in 3 of 12 grids than conventional methods (with a range of 101 to 213 lbs. and a mean of 167 lbs.).
8. Grid sampling and variable rate fertilization produced more recoverable sugar per acre than conventional methods in 8 of 12 grids (with a range of 149 to 834 lbs. and a mean of 401 lbs.).
9. Grid sampling produced less recoverable sugar per acre than conventional methods in 4 of 12 grids (with a range of 37 to 506 lbs. and a mean of 170 lbs.).
10. Grid sampling and organic matter adjustment produced more recoverable sugar per acre than grid sampling and variable rate fertilization in 8 of 12 grids (with a range of 24 to 727 lbs. and a mean of 297 lbs.).
11. Grid sampling and organic matter adjustment produced less recoverable sugar per acre than grid sampling only and variable rate fertilization only in 4 of 12 grids (with a range of 31 to 728 lbs. and a mean of 418 lbs.).

Acknowledgments

1996 Sugarbeet Research and Extension Reports. Volume 27, pages 92-97.

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