Polarised light detects spinach health
flailing raw plant materials.
Researchers in the US have uncovered a picture of plant health, from spinach to corn, that is invisible to the naked eye.
Using a portable light source and detector technology, the researchers can differentiate minute differences in leaf colours - indicators of over- or under-fertilisation, crop-nutrient levels and perhaps even disease.
"With our technology, we are able to easily see what is hidden from conventional instruments," says US researcher Steve Finkelman.
According to the scientists, the system eliminates interference from light reflected at a leaf's surface, allowing observers to see light re-emitting from within.
The proposed methods could be used to optimise fertiliser use and to detect invasive species that can lead to huge crop losses.
"The relatively low cost of these sensors and large markets in which they could be used, should promote prompt commercialisation of the technology following successful demonstration," the scientists have commented previously.
Depending on the plant, leaves reflect, transmit and absorb varying amounts of light. Polarised light that enters a leaf's interior can lose its polarity and be re-emitted as "depolarised" light.
The depolarised light reveals nitrogen content and other properties the proprietary sensors in the N-Checker (the new tool) can detect.
Changes in nitrogen levels change the way light interacts with the molecules in the leaf, characteristically affecting the spectrum of light that re-emits from the plant. Chlorophyll molecules, in particular, contain nitrogen atoms that play a critical role in photosynthesis.
"Other devices use both red and infrared wavelengths,"says Finkelman. "Those devices tend to be imprecise because they measure bulk chlorophyll content, which can result from a number of factors."
By using two specific, visible, red wavelengths, the N-Checker can differentiate among the several types of chlorophyll molecules and therefore reveal nitrogen-dependent plant health information.
According to the scientists, their tool can take 1000 measurements per second - at least every 10th of an inch - while moving at roughly 5 miles an hour. At that speed, a farmer could survey and fertilise tens of acres in a day, or hundreds of acres per day with a multi-sensor system.
