NITROGEN MANAGEMENT IN A WHEAT/POTATO/SUGARBEET CROP ROTATION

Lance Reitmeier M.S. Candidate, NDSU, Fargo, ND
David W. Franzen – Extension Soil Specialist, NDSU, Fargo, ND
Joseph F. Giles – Associate Professor, NDSU, Fargo, ND
Allan W. Cattanach – General Agronomist, American Crystal Sugar Co., Moorhead, MN
Norm R. Cattanach – Research Specialist, NDSU, Fargo, ND

The purpose of this experiment was to determine whether or not high nitrogen levels are the cause of historically poor sugarbeet quality in a four-township area of Pembina County, ND. If nitrogen was determined to be the problem, the purpose would also be to deal with this problem through the modification of sampling techniques and nitrogen recommendations.

The area of concern, including the townships of Elora, Lodema, St. Thomas north, and St. Thomas south, has a high density of small grains, potatoes, and sugarbeets in the crop rotation. Past records have suggested that high nitrogen levels remaining at harvest were the primary cause of the low sugarbeet quality throughout a majority of these fields.

This project was conducted using full-scale approach on four different 40-acre fields. Using the full-scale approach, the whole field could be analyzed for relationships between topography, foliage color and nitrogen content, and soil nitrogen levels throughout the field.

Objectives:

  1. To determine the source of excess nitrogen, if nitrogen is found to be the problem.

      2.  To modify sampling methods to identify nitrogen levels relevant to sugarbeet production in a wheat/potato/sugarbeet crop rotation.

Procedures:

1997 Research

Two sugarbeet fields were selected for the study in the fall of 1996. These fields, which were to be sugarbeets in 1997, were split into three-acre grids and soil sampled down to four feet. Nitrogen applications were made randomly throughout both fields using variable rate and conventional recommendation methods.

These fields were split into -acre grids in June of 1997. Sample strips were thinned to a uniform population (150 beets/100’) on all grids. Four petiole samples were taken, on all grids, every two weeks starting in late July. The samples consisted of 24 petioles from each grid. The petioles were tested for nitrate-N content. Aerial images and satellite images were also taken throughout the growing season.

The test strips were harvested in mid-September. The tops were harvested to determine dry matter yields and total nitrogen content, and the roots were analyzed for quality at the tare lab of American Crystal Sugar Co. in East Grand Forks, MN.

Soil samples were taken on all of the grids at four different depths, including: 0-6", 6-24", 24-48", and 48-72". The soil samples were tested for nitrogen at all depths, and organic matter on just the 0-6" depths.

Two 40-acre potato fields were also selected for this study in the fall of 1996. These potato fields were split into -acre grids. One petiole sampling was taken from each grid, each sample consisting of 24 petioles. Aerial Ektachrome images and satellite images were also taken throughout the growing season on both of these fields.

At the end of August, potato vine samples were taken from a ten-foot section out of each grid. The vines were tested for total nitrogen to determine if any nitrogen credit was available for subsequent crops. After harvest, soil samples were taken similarly to those taken on the sugarbeet fields. In addition, potato culls were taken from a 25 square foot area to determine cull yields and nitrogen content of the remaining potatoes.

Topographic maps were also produced of these two potato fields by AGSCO of Grand Forks, ND. These were produced to identify any relationships between topography, nitrogen content of the soil and tops, and the aerial and satellite images.

Nitrogen recommendations were made in the spring of 1998 for one of the 1997 sugarbeet fields, that was to be wheat, and for both of the potato fields, that were to be sugarbeets. The recommendations were made using the aerial images, nitrogen content of the tops, and the soil test nitrogen levels.

1998 Research

The two sugarbeet fields for 1998 did not receive any additional nitrogen fertilizer. The remaining soil nitrogen following the potatoes, and the nitrogen credit given from the potato tops was deemed sufficient for sugarbeet production. The field that was planted to wheat was given as high as a 100 lb./A nitrogen credit following the sugarbeets.

The sugarbeet fields were split up again into -acre grids, the same grids that were used on the previous year’s potato crops. These grids were located with the use of an Omnistar backpack DGPS unit. Petiole samples, aerial Ektachrome and satellite images, roots, tops, and soil samples were collected and analyzed the same as in 1997.

The field that was planted to wheat was soil sampled throughout the summer to track the nitrogen mineralization that was occurring, primarily from the previous year’s sugarbeet foliage. The grids from the 1997 sugarbeet field were located with the Omnistar backpack DGPS unit. The center of each of these grids was sprayed with glyphosate at the wheat emergence stage and throughout the growing season to keep an area vegetation free. Soil samples were taken from this area in 0-6" and 6-12" depths every two weeks, starting at wheat emergence, until the end of June. All of the samples were tested for nitrogen content. Another sample was taken from these grids in mid to late August down to four feet. This sample was taken because it was hypothesized that a significant amount of nitrogen leaching may have been occurring throughout the summer.

Results and Discussion:

The sugarbeet yield and quality of the variable-rate applied vs. the conventionally applied grids showed no significant differences between the two in 1997. It is believed to have been the result of the excess amounts of nitrogen available to the beets that caused these observations to occur. The majority of the tare samples were high in amino-N and low in sugar content, therefore suggesting the influence of excess nitrogen. The results were quite variable between the variable-rate and conventional applications.

The 0-6’ nitrogen test suggested that the soils were depleted of nitrogen following the sugarbeet crop, figure 1. What seemed to be occurring on both of the sugarbeet fields was that the crop was extracting the excess nitrogen from the soil and storing it in the tops, as seen in figure 2. The percent nitrogen in the tops averaged 3.17% over this field, which would suggest a fairly low carbon to nitrogen ratio, and a significant amount of mineralization that could potentially occur. Similar results were obtained on the other sugarbeet field in the 1997 study.

Given the soil test results and the total N in the tops, along with the imagery from the aerial Ektachrome photographs, various nitrogen management zones were identified. The petiole samples that were taken did not prove to be a useful tool in making nitrogen recommendations. Analysis of the petioles displayed a weak correlation between the nitrogen in the tops and the soil test nitrogen levels.

Overlaying the soil nitrogen map with the map of the total nitrogen in the tops, the expected amount of nitrogen available for wheat was obtained in figure 3. The higher levels of this field were given as much as 100 lbs./A. for a nitrogen credit to the following wheat crop. Wheat yields obtained, following these fertilizer recommendations for 1998, are depicted in figure 4. The high yields and uniformity of this field suggests that the wheat showed no signs of nitrogen deficiency, excluding the drowned-out spot in the center of the field. The cooperator was also quite pleased with the protein content of this field.

The mineralization study suggested that there were areas within the field in which over 100 lbs./A. of nitrogen mineralization occurred. Support is given to the nitrogen quantities being obtained from the previous years sugarbeet tops due to the fact that;

  1. Large amount of nitrogen were found in the sugarbeet tops, and
  2. Significant nitrogen mineralization was observed early in the growing season.

Figure 5 displays the quantity of soil-N that was available from mineralization at mid-August. Further research is being proposed to study the rate of mineralization and nitrogen quantities obtained from various residues within the soil.

Both of the potato fields that were studied in 1997 showed relatively high nitrogen levels remaining at harvest to the 0-4’ levels, figure 6. Since it was hypothesized that the sugarbeets were taking up nitrogen below the 4’ level, soil samples were taken down to 6’. The soils on these fields, which are primarily a Glyndon silt loam, would favor the root development of the sugarbeets down to these levels. With the additional 2’ depth it was found that there was a large amount of additional nitrogen between the 4-6’ range that was available for the sugarbeet crop. Figure 7 presents these high nitrogen levels.

The tops of these potato fields were given a nitrogen credit over the majority of both fields ranging between 20 and 30 lb./A.. The quantities of nitrogen credited to the sugarbeet crop from the potato tops are depicted in figure 8.

Given the high soil test nitrogen levels that remained in the soil, and the nitrogen credit assumed from the potato tops, it was suggested that no nitrogen fertilizer be applied to these fields for the 1998 sugarbeet crop. Having applied no nitrogen fertilizer, the following yield and quality data from these fields is shown in table 1.

Table 1 - 1998 sugarbeet yield and quality results
 

Tons/Acre

% Sugar

Rec. Sugar/A

% SLM

Nitrate Grade

$/Acre

Section 34

27.5

17

8580

1.4

2.2

1115

Section 29

22.9

17.3

7236

1.5

1.5

1242

After the sugarbeet crop was taken off in the fall of 1998, soil samples were once again taken to the 6’ level. Similar observations were made from the fall of 1998 as were made in the fall of 1997. The soil test nitrogen levels suggested that the sugarbeets were acting like a "vacuum," and depleting the soil of the high nitrogen levels that were previously seen. This observation is made in figure 9.

The nitrogen in the tops remained high, as was observed in 1997. The levels were not, although, as high as were found in 1997, figure 10. This would suggest that it was definitely to the cooperators benefit to refrain from applying nitrogen fertilizer to the 1998 crop.

With the nitrogen that remained in the soil following the sugarbeets, the amount of nitrogen that was in the tops, and the use of the aerial Ektachrome images (figure 11), nitrogen management zones were defined and recommendations were made accordingly.

Although the topographic maps showed a strong relationship between the hilltops and the high nitrogen areas (figure 12), they were not used because the imagery proved to be such a useful tool in making recommendations.

Nitrogen recommendations are depicted in figure 13 for the 1999 wheat crop, giving as high as a 100 lb./A. nitrogen credit again, and a 60 lb./A. credit in two other zones within the field. The rest of the field was to be conventionally fertilized. 

Summary:

We have found that the cause of historically low sugarbeet quality in the four-township area of southern Pembina County, ND is due to the excess nitrogen available to the sugarbeets during the growing season. This problem may take a few years to correct, but it would appear that the following processes are a step in the right direction.

  1. Take a nitrogen credit for sugarbeet tops by sampling the tops under the direction of aerial/satellite imagery.
  2. Soil sample between wheat and potatoes to two feet.
  3. Soil sample following potatoes to six feet in areas directed by aerial/satellite imagery.
  1. Consider taking a previous crop credit for the potato tops if sufficient nitrogen is found in the tops to justify such a credit.

The use of new technologies, such as aerial and satellite imagery have proven to be a successful tool for this project. These technologies, along with the directed soil sampling and plant sampling for nitrogen will restrict making matters worse, and should eliminate this problem over time if strict nitrogen management techniques are followed. Some of the conclusions of this project and recommendations as of this date include:

Acknowledgments:

Funding for this project has been provided in part by the Sugarbeet Research and Education Board of MN and ND and American Crystal Sugar Co. of Moorhead, MN. American Crystal also provided the Satellite images used. The aerial Ektachrome images were provided by AGSCO, and Simplot was responsible for providing the topographic maps. All of the soil samples, and most of the plant samples, were analyzed in the soil lab at NDSU in Fargo, ND. Agvise of Northwood, ND also ran some of the sugarbeet top analysis. Pete Carson from St. Thomas, ND was the cooperator, and was an exceptional person to work with throughout this project.