ISSUE #383

383 - Soil Testing and Nitrogen Critical to Quality


Soil testing is a critical component to ultimately harvesting and delivering a high quality sugarbeet crop. Sugarbeets are good scavengers of nitrogen so any excess N available in the soil profile even down to 6’ or more can have a negative impact on crop quality.

A 0-2’ soil test is required as stated in the five-year shareholder agreement and a 2-4’ test is strongly recommended. A 4-6’ test is also being considered in some of the lighter soil areas of the Valley. Figures 1 & 2 show the relationship between sugar % and SLM % at 0-2’ and 2-4’ depths. At both depths there is an inverse relationship between sugar % and SLM as soil test increases. As soil test N rises, sugar % decreases and SLM % increases. Note that, regardless of added fertilizer, as soil test N increases quality decreases! Based on this data, starting out the year prior to beets with your N under control is very important!

Figure 1 


Figure 2


Nitrate grade is a measurement that indicates the amount of nitrogen in the beet at harvest. Table 1. matches the nitrate grades for the 1999 crop with quality, yield and $ return. Note that neither the highest yield nor the highest quality resulted in the best return/acre! Too low of a nitrate grade may indicate that the crop is or was deprived of nitrogen and anything in excess of 2.9 would be considered prohibitive to maximizing your $ return/acre.

Table 1. Nitrate Grade – Red River Valley Average – 1999 Crop Year

(Assuming sugar at $0.205/pound and hauling cost @ $5/ton)         $ Gross 
Nitrate Grade Harvested AcresTons perSugarSLMRecoverable Sugar/Ton Recoverable Sugar/Acre $ Gross $ Gross Payment/Acre Less Hauling Cost 
GradeFields  Acre       
0.1-0.9  21  527.8  18.1  18.09  1.13  339  6136  $36.27  $656.41  $565.91 
1.0-1.9  739  47,510.5  19.5  17.96  1.24  334  6513  $35.28 $687.99  $590.49 
2.0-2.9  2554  190,324.1  20.3  17.64  1.34  326  6618  $33.56 $681.26  $579.76 
3.0-3.9  2126  154,217.0  20.3  17.19  1.47  314  6374  $31.18 $632.98  $531.48 
4.0-4.9  647  38,490.5  19.6  16.53  1.64  298  5841  $27.78 $544.46  $446.46 
5.0-5.9  100  4,653.4  19.0  15.67  1.85  276  5244  $23.29 $444.44  $349.44 
6.0-6.9  148.6  12.6  13.61  2.05  231  2911  $14.13  $177.98  $114.98 

Conclusions From Table 1 Are:

  1. As nitrate grade increases, recoverable sugar/ton decreases.
  2. As nitrate grade increases, recoverable sugar % decreases.
  3. As nitrate grade increases, SLM % increases.
  4. Highest recoverable sugar per acre occurred at a range of 2.0-2.9-nitrate grade. However, the highest return per acre was at 1.0-1.9 nitrate grade!

Basic Guidelines to Conventional Soil Testing Preceeding Sugarbeets:

  1. Need 15-20 soil cores per field.
  2. Sampling from uniform areas will give you the most representative sample results. If areas of the field differ due to crop history, soil type, topography, etc., you should:

    • avoid sampling these areas and,
    • consider sampling this area as a separate field.

  3. Following small grain, soil sampling can begin as early as August 15th. By adding a nitrogen credit of 0.5 lb. of N/acre/day to the soil test N from August 15th through September 15th, an accurate measurement of N can be made. Two advantages of testing early:

    • will get a more uniform sample prior to tillage and,
    • sample results should be in hand in time for fertilizer spreading.

  4. Following field peas or edible beans, soil sampling should be delayed until after September 15th. With corn, sunflowers and soybeans, sampling immediately after harvest is the norm.
  5. A more uniform, accurate soil sample will be obtained if taken prior to any tillage operation.
  6. Testing for most of the major and minor elements can be done at any time during the year. The exceptions are nitrogen (N), sulfur (S) and chloride (CL). Testing for these three is best in the fall or early spring.

Zone Sampling

Soil sampling based on topography, soil type, or a varying nutrient credit from a previous crop. These are all examples that may warrant dividing a field into areas of different fertility needs. An example of this is the nitrogen credit from beet tops that can be applied to crops following sugarbeets.

  1. 8-12 or more cores should be taken randomly from each zone.
  2. The advantage of zone sampling – more efficient use of fertilizer – less over and under fertilizing large areas of a field.

Grid Sampling

This method requires that you divide the field into 1 to 5 acre blocks with 8-12 core samples taken within a 10-20’ radius in each block. Fields showing a lot of variability may be good candidates for grid sampling.

OTHER Points of Interest:

* The average sugar % and SLM % for the closest sample date to August 25th for the last 15 years is shown below.

5-year PeriodSugar %SLM %
1995-1999 14.16 1.68
1990-1994 14.24 1.84
1985-1989 14.94 2.06

These numbers are from in-field samples taken by the Ag staff over that time period. Be aware that % sugar from headlands is normally about 1% lower than the main field. The new pre-pile payment system will hopefully encourage all growers to attempt to increase the quality of prepile beets. This can be done through elimination of headlands, variety selection and nitrogen management.

*At you will now find an N, P, K fertilizer calculator. When you get to our home page, select Agronomy, then Ag Calculators. The N, P, K calculator asks you to enter your soil test information then calculates your fertilizer needs. Next you’ll enter the local fertilizer prices and select the fertilizer type you plan to use. The calculator will then generate the costs associated with different fertilizer formulations and may aid in fertilizer selection based on what makes the most economic sense. Comparisons of effect of price differences can be quickly made.

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