1. Grid Sampling: Point vs. Random
Precision Agriculture
February 2, 2001

2. Grid Sampling

3. Grid Sampling

4. Cell-random
STP

5. Soil test pH Area ave =5.9; CV = 11 Pt. ave = 6.0; CV = 11 1 2 3 4 5 67 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Soil test pH
Area ave =5.9; CV = 11
Pt. ave = 6.0; CV = 11

6. Lime requirement Area ave =0.81; CV = 40 Pt. ave = 0.64; CV = 58 1 2 37 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Lime requirement
Area ave =0.81; CV = 40
Pt. ave = 0.64; CV = 58

7. Soil test-P Area ave = 139; CV = 55 Pt. ave = 144; CV = 51 1 2 3 4 5 67 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Soil test-P
Area ave = 139; CV = 55
Pt. ave = 144; CV = 51

8. Soil test-K Area ave = 193; CV = 23 Pt. ave = 199; CV = 25 1 2 3 4 5 67 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Soil test-K
Area ave = 193; CV = 23
Pt. ave = 199; CV = 25

9. Grid Sampling: Point vs. Random
Summary:
Generally, there is little difference between point and random sampling of a cell in a field-grid.
Two of 24 cells differed by more than 100 % (STP) and are likely a result of high variability within the 1-acre cells.
Either approach may be useful to identify “management zones”, where adjacent cells may be treated similar with production inputs.
Spatial variability appears to decrease as resolution increases (e.g. size of area under inspection decreases)