"Available" Nitrogen?

goodtogrow 4/29/2022, 1:09 am

Can anyone help me understand more about what is meant by "available" nitrogen in soil? I've read that just because nitrogen is "in" the soil that a plant lives in, it doesn't mean that that plant can actually use that nitrogen. What does that mean? Can anyone please help me understand this?
thinking

**sanderson** 4/29/2022, 3:57 am

Very simple explanation of the Nitrogen Cycle)

Air is made up of 78% atmospheric nitrogen (N2). Plants can't use this form of nitrogen. Certain bacteria in the top inches of dirt (top soil) can convert N2 into ammonium (NH4+) which plants can use. Also, when plant and animal matter decay, they are decomposed into ammonium (NH4+). Sounds like our compost! Very Happy

Meanwhile in the soil (or our Mel's Mix), nitrifying bacteria convert NH4+ into nitrites (NO2-). Then other bacteria and Archaea convert NO2- into nitrate (NO3-) which the plants can also use. Some NO3 remains in the soil (our Mel's Mix) and other is washed out.

OhioGardener 4/29/2022, 9:15 am

Excellent description, Sanderson. To expand on your explanation slightly, this is the huge difference between organic soil/gardening and chemical fertilizer farming. When farmers plant corn seed, they drill anhydrous ammonia into the soil, which provides plant-available nitrogen to the corn. But, when an gardener plants corn seeds in the MM, there may be very little plant-available nitrogen available at that time. The root of the corn, though, will send out exudates to tell the microbes that it needs nitrogen, and the microbes will begin breaking down the organic martial to release the nitrogen.

Those interesting in this symbiotic relationship between the plants and microbes should read the book, "Teaming with Microbes".

**sanderson** 4/29/2022, 3:13 pm

Yes, commercial farming is very different from backyard gardening, especially SFG where we use compost for feeding the plants. Commercially made Ammonia NH3 verses organically made ammonium NH4+.

"Teaming with Nutrients" and "Teaming with Microbes" are two excellent books. Very Happy

I used the former for simplifying the nitrogen cycle.

goodtogrow 4/29/2022, 6:50 pm

Thank you both for that info, that helps a lot.
And I will check into those books!
Much appreciated, Sanderson and OG.

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