Chlorophyll content measurement for PhotosynQ

Hey folks – just wanted to give you a quickupdate. I’ve made several improvements to the Arduino code in the last few days so that it’ll be easier for users to create new protocols! We’ll have a few measurements before the start of the Beta. Often called SPAD, this measurement was first commercialized by Minolta and they remain a big seller of chlorophyll content measurement instruments, specifically the SPAD 502 meter (http://www.specmeters.com/nutrient-management/chlorophyll-meters/chlorophyll/spad502p/).

SPAD measurement

Chlorophyll content can be a proxy for N levels in plants, and therefore indicate when additional fertilization is required. Here’s a quick little paper which uses SPAD measurements on 2 crops to predict N application: http://www.hort.cornell.edu/uhi/research/articles/horttech12%284%29.pdf. This technique is particularly proven in corn and several other major commercial crops – so pretty darn useful!

How it works

The SPAD meter measures transmission of 2 wavelengths (650nm and 940nm) through the leaf. The 650nm correlates with the presence of chlorophyll, while the 940 measures the leaf thickness. The ratio of the two tells you roughly how much chlorophyll is in the leaf (measured in SPAD units). This is a relatively easy measurement because neither light sources need bandpass filters (a bandpass filters out light outside of a narrow spectral band, for example from 640 to 660, to provide a more pure light source).Other companies have developed other techniques, like opti-sciences, which are a bit better (they don’t require that you clamp on both sides, they don’t require that the leaf completely cover the light guide, can wider range of chlorophyll concentration, etc.). That technique compares 700nm with 730nm which also correlates to chlorophyll content – however, this technique requires bandpass filters which are expensive. Read more about it here: http://optisci.com/ccm300.htm.

So we’re going with the good old SPAD measurement because we can do it with out current device setup and, most of the time, it’s just as good as the newer method.

Help make PhotosynQ SPAD-tastic

We are looking for any beta testers interested in helping us correlate our SPAD measurements with Minolta (or other brand’s) SPAD readings. If you’re interested, please shoot me an email!

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