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Nitrogen Depleted?

Posted by wmarsich z7 NC (My Page) on
Tue, Dec 8, 09 at 7:04

My daughter is just finishing her science fair project. She has four worm bins which she fed different types of food (fruit, veggie, egg/coffee, and grass/leaves) for the last three months. The hypothesis was that the bins would produce different levels of nutrients that would then could be best used for optimal production of different plants or at different times of plant development. Well the day arrived to test all the soils on Sunday. She had to wait an extra day just to let the soil settle in some of the water, but she completed all the tests last night. Our surprise (and she re-did each test) all of the bins came up Nitrogen deficient??? They had varying degrees of Potash and Phosphorus and varying levels of PH, but no color came up on the Rapitest for Nitrogen. She has one week before she has to turn everything in, any thoughts out there???

Follow-Up Postings:

RE: Nitrogen Depleted?

Vermicompost is not a fertilizer as such, but a soil conditioner. Having said that I would have expected the result to give a significant nitrogen showing. I'm not familiar with how the tests work (might be worth giving the manufacturer a call) but the reagents in the test might be looking for inorganic nitrogen (chemicals)which dissolves in water for rapid release, whereas the nitrogen in Vermicompost is tied up in organic compounds and released to the plants slowly, as required by the plant. Therefore it wouldn't show up in the water in your test tube, but stay attached to the 'soil' at the bottom. That's why VC is better than chemical fertilizers - it doesn't get washed away into the water table with the first shower of rain.
It might be worth calling a local agricultural college and asking them if there's any other test she could use to measure the actual nitrogen content. But even so it would be hard to compare the available nitrogen with the benefit your compost would have for the plant. There a a number of serious vermicompost producers out there who sell and market their stuff, so presumably they are able to measure the quality in some way, and might be able to share some information. Sorry I couldn't be of more help. Best of luck with it!

RE: Nitrogen Depleted?

I have always read that nitrogen is hard to test for and almost worthless with the at home tests

It sounds like a very good experiment maybe a lab could help with testing
in mn when you send sample to the U they will not test it for nitrogen

RE: Nitrogen Depleted?

Were the samples pulverized or otherwise well blended into the test liquid? Did she use a positive control for the N test, like a commercial compost with a specific N rating on the label? This would show that her methods are good.

I would tend to agree with cathd66's comment that the primary benefit of vermicompost is as a soil conditioner, but I've also read that it typically contains 6 times the NPK as regular compost. When I think of humus, I automatically think of black, sticky worm castings.

Good luck. I like the study design.

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