Wednesday, January 27, 2010

Week 5: Salt

I have irrigated 5 times now with wastewater at 800 ppm salinity but I am collecting water from the Wetting Front Detectors at 20 cm and 40 cm depths at substantially lower salinity (442 and 672 ppm respectively). Theory teaches us that plants will remove water and leave the salt behind, so the soil salinity levels should be starting at 800 ppm and going up. It has not rained, and I do not think I’m washing the salt deeper into the soil. Here is my guess at what is happening. If domestic water contains dissolved calcium and magnesium (‘hard’ water), these ions react with the detergent and inactivate it. Washing powders contain water softeners that bind with the calcium and magnesium to stop this happening. I think the water softener is reacting with ions in my soil making complex precipitates. Although I plot salt in parts per million on the graph, I actually measure the electrical conductivity and convert this to ppm using a fudge factor for common solutes. Maybe this is my problem?

1 comment:

Jacqui & Richard said...

Wow, that's some lateral thinking! How long will that continiue? Will you saturate the precipitate making properties of the soil and then see salt accumulation?
I meant to visit and say goodbye to Emily this evening but... I'll try and see her after work briefly.