Precision Nutrient Management: Soil Sampling Strategies

1. Precision Nutrient Management:Soil Sampling Strategies Hailin Zhang and Gordon Johnson Department of Plant and Soil Sciences

2. Precision Nutrient ManagementStrategies Grid soil sampling Apparent Electrical Conductivity Yield monitor/mapping Sensing techniques

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

4. Recognize Field Nutrient Variability Nitrate - Nitrogen lbs/acre 0-30 31-40 41-50 51-60 61-80 >80 (Nitrate-N within a 75’ x 75’ plot)

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

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

9. The greatest potentialfor error in soil testingis in taking the sample

10. Soil Sampling Strategies * * * * Whole field composites: Composite sample representing the average nutrient status of the field * * * * * * * * * *

11. 20 cores are needed to make a representative composite sample in order to get reliable soil test results

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

13. 120 P Changes with Depth (no-till) Depth P (ppm) 0” 2” 55 6” 35 12” 31 24”

15. Soil Sampling Strategies 2. Zone composites: Break field based on known or expected source of variability

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 * * * * * * * * * * * * * * * * * * *

17. 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 15 cores of soil from a 0-6” depth

18. Whole field • 1 acre grid • Sub-grid • Center area • Point X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X * * * * * * * *

19. Comparison of Whole Field Sample between 2000, 2001 and 2002

20. Comparison of Area of Sampling for 2002

21. Whole field average.

29. Whole field sample pH: Team 1: 6.0, 6.1 Team 2: 6.4, 6.4

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

34. 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

35. Analysis Costs of Various Sampling Intensities *at $10/sample

36. Analysis Costs of Various Sampling Intensities *at $10/sample; **at $10/hour and collecting 1 to 5 samples per hour

37. 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