Measuring nitrogen using TDS meter ?

[Ray]

First and foremost, TDS meters are notoriously inaccurate. They are just cheap electrical conductivity meters with a built-in conversion factor to TDS, and the true conversion would change from one fertilizer formula to any other.

If you want to use the meter as a guide, mix up a small quantity of fertilizer at a known concentration based upon calculations, and measure it's TDS. Then double that concentration (so you can cut it it half and still use it) and measure that.

Then make a graph of the TDS readings and the actual ppm N, draw a line through both data points, and you have a reasonable, if not entirely precise, calibration chart.

[Evendozen]

Originally Posted by Ray

First and foremost, TDS meters are notoriously inaccurate. They are just cheap electrical conductivity meters with a built-in conversion factor to TDS, and the true conversion would change from one fertilizer formula to any other.

If you want to use the meter as a guide, mix up a small quantity of fertilizer at a know concentration based upon calculations, and measure it's TDS. Then double that concentration (so you can cut it it half and still use it) and measure that.

Then make a graph of the TDS readings and the actual ppm N, draw a line through both data points, and you have a reasonable, if not entirely precise, calibration chart.

I believe this meter is fairly accurate. I was quite surprised at the small amount fertilizer needed. Without testing I would have used way too much !