1. What about the window—won’t it break?
The 4mm thick optical sapphire is second (to diamonds) in hardness. Field tests and results from rocky areas show that window breakage is rare.
2. What are operating costs?
Based on average conditions, the operating costs for ground-engaging components—wear plate, window, row unit blades and bearings—are approximately $.25-.40 per acre ($.60-1.00 per ha). These costs may be slightly higher in sandy soil and lower in less abrasive soils. Data-Processing by Veris Mapping Center is required; cost $.25/acre ($.60/ha)
How stable and repeatable are the measurements?
The electronics, light source, and detectors have virtually zero drift due to operating temperature. The unprocessed sensor readings show excellent pattern repeatability.
4. What calibration is needed?
Operating instructions advise daily collecting a dark/light reference using the two-sided magnetic block provided. This is to insure components are working satisfactorily.
OpticMapper data can be calibrated to organic matter readings using a handful of lab-analyzed samples. Veris’ Mapping Center uses a proprietary multivariate regression analysis technique that includes data from EC and topography sensors, when it improves the calibration.
5. What about EC? Do I need both sensors?
On some fields, soil texture and soil OM correlate reasonably well. Fields with coarse, low OM soils and darker, finer textured soils will see similarity between the two sensors.
On many fields, soil texture and soil OM show different patterns, due to soil salinity, low OM clays, black sands, etc. On these fields, having EC and OM data means less ground-truthing to verify the patterns. And a prescription can be fine-tuned using the two layers--for example, a silt-loam soil will hold, use, and lose N differently than a silty-clay soil—even if their OM is identical.
6. Isn’t this amount of precision overkill? Can my big planter vary rates according to the refined map?
40’ cells overlaid on OM map shows that even large planters can take advantage of the extra precision provided by the OpticMapper.
7. How much moisture is needed?
Enough to allow row unit to penetrate to a 1-2” (2.5-3 cm) depth.
8. Won’t moisture skew the readings, since dark soil could either be higher in OM or merely wetter?
Soil will absorb more light—and appear darker, due to OM or to moisture—or both. If you’ve observed a bare-soil field drying after a rain, you’ve seen pockets of wet, dark soil. Remote imagery of bare soil has problems correlating to OM due to this micro-relief phenomenon. The OpticMapper operates underneath the ‘noisy’ surface layer where the moisture level is more stable, and where soil color is mostly related to soil organic matter variations. The best answer to this question is in the results: examining correlation stats and viewing validation samples overlaid on Veris maps.
9. Will it work in no-till?
Yes, fluted coulter ahead of row unit cuts residue and opens a slot for the row unit to follow. Successful mapping directly behind corn combine will depend on crop yield, distribution of residue, and other factors. Mapping through corn residue after winter’s decomposition typically poses no problems.
10. Is this level of precision needed—why not just use a free soil survey?
The NRCS website displays this warning when downloading field-scale surveys:
NRCS posts this for good reason—they know how the surveys were created, and how they were intended to be used. Issues with soil surveys include:
Inclusions: Depending on the survey scale, soil surveys allow 2-5 acre inclusions. These are areas of another soil type within a larger soil type.
Errors: Many of the errors in soil surveys were a result of not having GPS technology available when the surveys were done.
Transitions: soils don’t change on a line—but are a continuum. A soil survey indicates changes as a line, when in reality there is often a sizeable transition zone between soil types.
Changing seed population rates at the soil survey lines, instead of where the soil actually changes, could easily cost over $20/acre in lost yield—every year. That makes the ‘free’ soil survey very costly.
11. What about yield data or remote imagery—is this better?
Crop imagery and yield data show crop symptoms. This can be extremely valuable, especially if in-season remediation can occur. But using only maps of symptoms to diagnose productive potential is like a doctor refusing to use an x-ray or MRI to diagnose an internal medical condition. In modern medicine, doctors use both—they use the best technology available to investigate the root cause of problems, as well as input from the patient about their symptoms. Agriculture is best served with a similar approach.
Regarding bare soil imagery: this can be effective if conditions are ideal, but can easily be skewed by surface soil moisture.
12. What is the data format? How can I generate maps?
EC data is in an ASCII format that can be imported into most mapping programs. OpticMapper data is in a proprietary format that must be processed by Veris Mapping Center for a per acre charge of $.25 ($.60/ha). This process is critical to insuring that the OM estimation is correct. It includes a filtering and quality control check for EC and OpticMapper data, using proprietary key quality indicators. Veris will calibrate the field to lab samples, perform a cross-validation, and return a final field file containing all EC, OM reflectance, and OM Calibration data.