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Application Note: OpticMapper

Proper Mapping Techniques

1. Equipment Testing. Before mapping, perform equipment tests using electronics test

load and reference block, as recommended by Operations Manual.

2. Recognize Effects of Soil Condition. In order to generate high quality OM data, it’s

crucial to understand that field history, soil conditions, and equipment settings can affect

estimations of OM from OpticMapper measurements. The most important consideration

is soil moisture: moist soil and organic matter are both darker in color than dry soil and

low OM, which could lead to confusing and erroneous estimations of soil organic matter.

Effective OM field mapping requires consistent moisture levels—of course soils have

natural differences based on soil water-holding capacity--sand will have less moisture,

clay more. What are critical to prevent are management-related moisture

inconsistencies. These can be caused by:

a) A field having two or more moisture conditions, due to tillage, cropping, or irrigation

differences (Figure 1). To avoid these situations, treat each condition as a separate

field: map differing conditions on separate files, and make sure both conditions are

represented with calibration samples.

Figure1. Moisture variation between two fields mapped as one

b) Adjustment of OpticMapper during mapping—changing depth or down-pressure

which causes sensing depth to change (Figure 2). If in-field adjustments are required,

Summary of content (5 pages)

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Application Note: OpticMapper Proper Mapping Techniques 1. Equipment Testing. Before mapping, perform equipment tests using electronics test load and reference block, as recommended by Operations Manual. 2. Recognize Effects of Soil Condition. In order to generate high quality OM data, it’s crucial to understand that field history, soil conditions, and equipment settings can affect estimations of OM from OpticMapper measurements.
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begin a new file and make sure both conditions are represented with calibration samples. Figure 2. Data shift due to adjustment of OpticMapper during mapping c) Inconsistent row unit penetration—if the OpticMapper encounters a wheel track on one pass and soft soil the next, there will be a different sensing depth for the two passes. Similarly, if one pass is in bare soil and the next behind the combine pass with thick residue, there could be a moisture difference at the sensor operating depth.
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Figure 4. Mapping at a slight angle to main fieldwork pattern Note: Inaccurate estimations of organic matter due to soil moisture conditions can have serious consequences for applications of nitrogen and population. 3. OM differences due to field history. It’s reasonable to expect fields with different histories that have been merged to have an actual shift in reflectance and OM.
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- if not possible to map at angle, maintain soil and residue consistency for OpticMapper row unit; avoid wheel tracks and heavy residue strips if possible. -double back (also called skip-pass) if feasible as shown below (Figure 5); this provides a more stringent pass-to-pass repeatability test Figure 5. Double-back or skip-pass method 5.
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Figure 6. Examples of proper sample selection (left) and improper (right). Problems are: samples do not represent full field—none north of waterway; samples are at edges, on transition zones or in ‘noisy’ areas; samples do not represent widest possible range of values.