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Using Remote Sensors to Discriminate Between Healthy and Less Healthy Crops


Remote sensors are a valuable tool for conducting research at the CREC. This 2018 cropping season, ground-based sensors (GreenSeeker, Crop Circle) and unmanned aerial systems (UAVs) are being used to assess the effect of fertilizer application on crop health (vigor).

When turned on above crop canopy, these sensors absorb light reflected by the canopy. The sensors produce numbers called NDVIs that are a measure of crop vigor. More abundant canopy produces higher NDVIs (between 0 and 1). Here are examples of mid-season assessment of wheat and barley for some 2018 trials at the CREC.

Figure 1. Two barley varieties gave higher NDVIs indicating a more vigorous crop from sulfur fertilization.

Figure 2. Phosphorus application enhanced wheat vigor as expressed by NDVI.

To decide whether top-dressing N would improve grain yields, the NDVI for a well fertilized plot (160 lbs N in this trial) was divided by NDVI of the check (which did not receive N fertilizer). This ratio gave us the response index (RI). An RI of 1.1 suggests we would expect a 10% yield increase if additional N was applied (Table 1).

Table 1.  A ground-based sensor was used as a decision tool to
determine top-dress N was not needed in this trial to enhance yield.

For further reading, visit a well written summary of remote sensor use in side-dress N applications for corn in North Dakota by Franzen, et al. available here: Active Optical Sensor Algorithms for Corn Yield Prediction and a Corn Side-dress Nitrogen Rate Aid.


Jasper M Teboh, Ph. D.
Research Soil Scientist

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