Subject: measuring total dissolved solids

From: [email-masked]
Date: 15 Jun 1996 14:07:27 GMT

I own a nursery.  I need help checking fertilizer content in my container soil.  My TDS pen reads 10 to 1990 ppm.  
Calibration solution is from the myron L company 442 - 3000 (3000 ppm / 442 ((2027 ppm NaCl)) 3900 microsiemens, 
3.9 millimhos). Whats that mean.  I cut the solution in half since my pen maxes @ 1990 ppm.  Please help with 
calibration as well as the best way to extract samples from container medium.  I want to maintain 200 -250 ppm N.  
What should the pen read considering 20-20-20 fertilizer used

			thanks,  the flower ranch
				[email-masked]

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From: [email-masked] (Clinton Morse)
Date: Mon, 17 Jun 96 13:58:50 GMT

>What should the pen read considering 20-20-20 fertilizer used

The general procedure for getting a TDS reading in a container medium is to 
water the container to 'field capacity' - completely watered with excess 
allowed to drain completely.  Then place your container over a suitable 
collection container and add water slowly (over entire surface area) and 
collect leachate until you have exactly twice the volume of solution as the 
volume of the container.  This is known as a 2:1 soil volume extract.  Measure 
your TDS from this leachate.  The conductivity will depend upon whose 
fertilizer you are using and what formulation.  Keep in mind you must first 
subtract the conductivity figure of your water supply.

The figure for Peters 20-20-20 General Purpose liquid is 0.80 Millimhos/cm 
equivalent to 200 ppm N and 1.00 = 250 ppm N

Figures will be different for different brands of fertilizer.
Hope this helps,