1. Precision Nutrient Management: Grid-Sampling Basis
Precision nutrient management has been around for some times, because varying the rates of crop inputs to meet site-specific needs makes economic and environmental sense. I am going to spend a few minutes to talk about grid sampling based nutrient management strategy.
Hailin Zhang and Gordon Johnson
Department of Plant and Soil Sciences

2. Precision Nutrient Management Strategies
Grid soil sampling
Apparent Electrical Conductivity
Yield monitor/mapping
Sensing techniques
As far as I know, these are the main strategies researched and applied. The first 2 are soil based and the other 2 are crop based.

3. Purposes of Soil Sampling
Measure the nutrient content or availability of the soil
Identify nutrient deficiencies
Predict crop response to added nutrients
Build a nutrient management plan
As far as I know, these are the main strategies researched and applied. The first 2 are soil based and the other 2 are crop based.

4. Recognize Field Nutrient Variability
Nitrate - Nitrogen
lbs/acre
0-30
31-40
41-50
51-60
61-80
>80
This graph shows the variability of nitrate-nitrogen in a 75’x75’ area of a field. Each small plot is a 5’x5’ square. Nitrate-N ranged from 25 lbs/acre to 102 lbs/acre over the area.
Each sample submitted for analysis should be representative of the the entire sampling area.
Avoid taking sample from any unusual spots, such as, manure piles, cracks, etc, to avoid any misrepresentation.
Data gathered from OSU Agronomy Research Farm
(Nitrate-N within a 75’ x 75’ plot)

5. What do you see in this field
What do you see in this field? Tremendous variability in plant growth probably due to grazing animal wastes.

6. Here is a winter wheat field at the Research Station in Perkins
Here is a winter wheat field at the Research Station in Perkins. Again tremendous differences in wheat growth. The forage yields ranged from practically zero to over 2,500 lbs/A. What we found the problem was low soil pH and high Al level. The forage yields were highly correlated to the Al saturation percentage.

7. Limiting Factors for Crop Growth
Factors are different for every field, therefore, remediation should be different too
Factors change from year to year
Factors limiting yield will interact
Have been realized the existence of field spatial variability, people have tried to account for them through management. Because:

8. Considerations for Soil sampling Strategies
Locate variability responsive to fertilizer and lime
Obtain a sample that accurately represents the area sampled
Balance cost of sampling with the value of information
As far as I know, these are the main strategies researched and applied. The first 2 are soil based and the other 2 are crop based.

9. The greatest potential for error in soil testing is in taking the sample
The farmer, or the person taking the soil sample, must provide the laboratory with a uniform, representative sample ... a critical component for the laboratory in providing accurate soil test results and fertilizer recommendations. Each sample, weighing only a pound or less, can represent millions of pounds of soil in the field. The greatest potential for error in soil testing is in taking the sample.

10. Soil Sampling Strategies
Whole field composites: Composite sample representing the average nutrient status of the field * * * * * * *
As far as I know, these are the main strategies researched and applied. The first 2 are soil based and the other 2 are crop based. * * * * * * *

11. 20 cores are needed to make a representative
composite sample in order to get reliable soil test results
By taking enough soil cores randomly in a field to make a composite sample, one can hit the average nutrient status repeatedly.

12. Scooping samples for extraction
One acre to 6 inch deep contains about 2 million lbs of soil

13. P Changes with Depth (no-till)
P (ppm) 0”
120 2” 55 6” 35
12”
Soil test P changes with depth. N,K, pH, and many other soil properties also change, especially when the field is not cultivated. Soil phosphorus on fields receiving top dressed poultry litter tends to accumulate near the soil surface.
A 0-6 inch sample is recommended for consistent and reliable soil test results. 31
24”

14. The key components of a good sampling technique.

15. Soil Sampling Strategies
2. Zone composites: Break field based on known or expected source of variability
As far as I know, these are the main strategies researched and applied. The first 2 are soil based and the other 2 are crop based.

16. Soil Sampling Strategies
3. Grid Sampling: Break field based on ordered pattern
Grid cell method: similar to whole field
Grid center method: point sampling X X X X
As far as I know, these are the main strategies researched and applied. The first 2 are soil based and the other 2 are crop based. X X X X X X X X X X X X X X X

17. 1. Random sampling of the entire field ,
Field Soil Sampling, Soil Testing, and Making Fertilizer Recommendations Exercise
1. Random sampling of the entire field ,
25 cores of soil from a 0-6” depth
filling two soil sample bags from the composite mixture
2. Grid-cell sampling
15 cores of soil from a 0-6” depth
3. High resolution
Have been realized the existence of field spatial variability, people have tried to account for them through management. Because:

18. Whole field 1 acre grid Sub-grid X X X X X X X X X X X X X X X
A grid soil sampling exercise was conducted in this 27 acre field for the last two years. The dept. of animal science manages this field and they will use it to receive manure from the new swine facility they are building.

19. Whole field sample pH: Team 1: 6.0, 6.1 Team 2: 6.4, 6.4
Soil pH raged from 4.5 to 7.5. You will know where lime should be applied.

20. Whole field
sample nitrate:
Team 1: 19, 18
Team 2: 28, 28

23. Whole Field Sampling: 114 & 117, 188 & 190
127
Grid sampling does reveal field nutrient variability
Whole Field Sampling: 114 & 117, 188 & 190

24. Whole Field Sampling: 206 & 196, 186 & 180
188
Grid sampling does reveal field nutrient variability
Whole Field Sampling: 206 & 196, 186 & 180

25. 5.6 Whole Field Sampling: 5.9 & 5.9, 5.6 & 5.6
Grid sampling does reveal field nutrient variability
Whole Field Sampling: 5.9 & 5.9, 5.6 & 5.6

27. Why Account for Spatial Variability of Soil Properties
Improve performance of ag. practices
Either costs go down and/or returns go up
Avoid over application that might be environmentally harmful
Have been realized the existence of field spatial variability, people have tried to account for them through management. Because:

28. Analysis Costs of Various Sampling Intensities
Grid Spacing
Area/sample
Costs*
Feet
Acres
$/acre 66
0.1
100
104
0.25 40
148
0.5 20
209 1 10
330
2.5 4
467 5 2
660
Conventional
*at $10/sample

29. Analysis Costs of Various Sampling Intensities
Grid
Spacing
Area/
sample
Analysis Cost*
Sampling Cost**
Total Cost
Feet
Acres
$/acre 66
0.1
100 20
120
104
0.25 40 10 50
148
0.5 5 25
209 1
2.5
12.5
330 4
1.25
5.25
467 2
0.65
2.65
660
0.40
1.40
Conventional
0.50
*at $10/sample; **at $10/hour and collecting 1 to 5 samples per hour

30. Choosing a Soil Sampling Strategy
Level of management and the resources to account for variability
Whole field sampling most appropriate when fertility is high and variability is low
Zoning/sub-field sampling may be most appropriate when
Location of variation known
Sampling areas are large
Limited resource
Grid sampling maybe appropriate if location of variation is unknown and variable rate applicator is available