So far, using autonomous robots to make soil measurements is somewhat futuristic. In general, robotics for scouting still has many limitations, including providing them with enough power to operate efficiently for long periods. However, hypothetically, you could mount one of these recently developed sensors onto a robot and if smart enough, the robot could even decide by itself how far away to make the next measurement based on geo-statistical field data.
You do this in mid-growth, when the plant just starts showing signs of nutrient stress that the human eye is not yet able to detect.
Although the pH sensor doesn't necessarily tell you the lime requirements, it does identify field areas needing lime. We use it to show the highs and lows on a map. Then we take manual soil tests and use those as a calibration for the map, which helps us to perform variable-rate applications.
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