Due Wednesday, September 3 rd at the beginning of lab
Student
Lab
TA
Objectives
1.
Learn how to collect a representative soil sample as a guide to nutrient management.
2.
Understand variability in field scale fertilizer requirements between random sampling, stratified random sampling, and grid sampling techniques.
Introduction
Collecting a representative soil sample is the first step in developing nutrient recommendations.
Proper soil sampling ensures nutrient recommendations are accurate for a specific management zone.
Specifics for obtaining a representative soil sample are outlined by Zhang and Arnall in OSU Extension
Fact Sheet, PSS-2207.
Many soil sampling strategies exist to encompass agronomic spatial variability and resolution.
Determining the appropriate soil sample strategy depends on agronomic, economic, and engineering criteria. The soil sampling strategies investigated in this exercise are random sampling, stratified random sampling, and grid sampling. Random sampling involves randomly sampling the entire field and composite the sample. Stratified random sampling divides the field into zones or areas based on agronomic criteria (soil zones in this exercise); randomly sample the zone and composite the sample.
Grid sampling uses geo-referenced fixed points and each grid is sampled and treated individually.
1

Extension Fact Sheet-PSS-2207
2

3

4

5

Procedures
An 8.3 acre field under management of the OSU Plant and Soil Sciences Department will be sampled. The field is located at the Efaw Agronomy Research Farm straight north of the intersection of
Sangre and McElroy. The field will be sampled utilizing three techniques (random, stratified-random, and grid). The random sampling will encompass randomly sampling the entire field. The stratifiedrandom sampling will encompass randomly sampling the two different zones (Norge and Norge-eroded) separately (Fig. 1). The grid sampling will encompass randomly sampling each of the 12 individual grids
(Fig. 2).
North
Figure 1. Sampling areas for stratified-random sampling technique.
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North
Figure 2. Sampling areas for grid sampling technique. Cell labels are located at the centroid point for each grid.
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Results and Report
Table 1. Soil test results from entire field random sampling, stratified random sampling, and grid sampling.
Sample Acres Crop Yield Goal NO
3
-N
†
N
Req.
‡
P
†
P
2
O
5
Req.
‡
K
†
K
2
O
Req.
‡ bu/ac lbs/acre
Entire field composite 8.3 Wheat
Zone 1 (Norge) 5.4 Wheat
Zone 2 (Norge eroded) 2.9 Wheat
Grid #1 0.48 Wheat
Grid #2
Grid #3
Grid #4
Grid #5
0.38
0.75
0.75
0.75
Wheat
Wheat
Wheat
Wheat
45
45
45
45
45
45
45
45
22
16
22
27
11
21
27
17
69 45
59 62
53 20
63 48
58 31
64 87
58 67
53 29
20 284
2 316
0
0
40 218 13
14 336 0
29 281
0 307
0
0
0 307 0
31 176 26
Grid #6
Grid #7
Grid #8
Grid #9
0.79 Wheat
0.32 Wheat
0.74 Wheat
0.75 Wheat
45
45
45
45
8
26
28
19
72 11
54 42
52 61
61 13
58 331
18 333
0
0
3 267 0
54 189 23
Grid #10
Grid #11
0.83 Wheat
0.83 Wheat
45
45
7
6
73 28
74 43
32 192 22
18 385 0
Grid #12 0.93 Wheat 45 9 71 20
†
Soil test units are lbs/acre for N and indexes for P and K.
‡
Requirements are lbs/acre for N, P
2
O
5
, and K
2
O.
40 155
Questions/Reports
Introduction: (2.5 pts) What/How/Why
For Questions 1 & 2 create a table similar to the above with proper headings, labels, title,
32 and any other required information.
1.
(2 pts.) Using the N, P
2
O
5
, and K
2
O requirements (lbs/acre) provided in Table 1, calculate the total amount of N, P
2
O
5
, and K
2
O needed to fertilize each zone or grid (lbs/zone or grid) and sum the total N, P
2
O
5
, and K
2
O needed for the entire 8.3 acre field (lbs/field) using the three sampling techniques (Table 2).
2.
(2 pts.) Assuming fertilizer costs of $0.45/lb N, $0.48/lb P
2
O
5
, and $0.31/lb K
2
O, calculate the total cost of fertilizer for entire 8.3 acre field using the three sampling techniques
(Table 2).
3.
(1 pt.) When is it typically best to soil sample?
4.
(1 pt.) What kind of field conditions would it be more favorable to grid sample?
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5.
(1 pt.) What are two factors that may influence the cell size for the grid sampling technique?
6.
(1 pt.) When soil sampling a field that has had nutrients applied in bands, why is it important to know where the previous bands were located?
7.
(2 pts.) If the cost of soil sampling and soil testing was not a factor, explain the benefit of soil sampling based on a management zone (soil type) and grids to make nutrient recommendations compared to a composite for the entire field. Consider total fertilizer costs in your explanation.
Conclusion: (2.5 pts) How does it apply to your field of study or will be applicable in your future career?
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