Nitrogen nodules on innoculated peas - how much N provided?

[grrlgeek]

Last weekend we took our last harvest and cut down the peas. I cut everything off below the soil line, turned it a bit, then used the plant material as top mulch. The spot is resting for a couple of weeks and corn is going to follow.

I uprooted a few of the root systems to see if they had formed nodules of stored nitrogen. Boy, did they! I am so pleased and excited.

I had planted a small patch of peas last fall without innoculating, and all I found when I dug them up was roots.

I do have a question though. It's a 4x6 area, and the pea planting was dense - every 2 inches. Fun to pick... yeah I wont be doing THAT again! How long does it take for the nitrogen to become available and how much will it provide? Should I still feed the corn, or will this be enough?

[imafan26]

A couple of things about nitrogen fixation. If you inoculate with the micorrhyzzae nitrogen fixing nodules increase a lot. If you are lucky though they are present in some soils naturally.

The legumes that are used the most are cowpea, hairy vetch and here we use sun hemp with uses the cowpea inoculant. If you are growing a legume for nitrogen fixation, you do plant it densely and till in everything, not just the roots right around flowering time when the nitrogen fixation peaks. If you wait to harvest the peas, by then, some of the nutrients have been transferred out of the system and will be lost. The tops also contain stored nitrogen as well as biomass.

The nitrogen stored in the plant tissues and the bodies of the bacteria as they decompose are slowly released back to the soil and become one of the nitrogen sources for the next crop.

Will it be enough for corn? It depends on how much nitrogen is available.

Legumes are actually heavy feeders of nitrogen. If there aren't enough bacteria to form nitrogen fixing nodules, they actually need to be given nitrogen or they don't produce much of a crop.

Even the nitrogen fixers do not fix well if there is a lot of nitrogen in the soil. Mother nature does not waste energy producing nitrogen if there is a more efficient way to get it. Most of the nitrogen that is fixed is consumed by the bacteria and some of it gets to the plant. When the plants and bacteria decomposed the nitrogen is released. Some of it will be consumed by other denizens in the soil and other bacteria convert it again to a form that will volatize off back to the air or leaches out from rain or runoff to water systems.

If your system is balanced there should be enough.

https://www.physicalgeography.net/fundamentals/9s.html

[grrlgeek]

If you are growing a legume for nitrogen fixation, you do plant it densely and till in everything, not just the roots right around flowering time when the nitrogen fixation peaks. If you wait to harvest the peas, by then, some of the nutrients have been transferred out of the system and will be lost. The tops also contain stored nitrogen as well as biomass.
https://www.physicalgeography.net/fundamentals/9s.html

Great link! Your reminder about killing the crop at flowering for the best fixation sent me digging through bookmarks all afternoon. I didn't grow the peas as a cover, per se, but their location and what would follow certainly played in role in my succession plan. I was hoping that having used an innoculant would be enough, or at least a good start at building a healthy and nutrient rich soil web. Last fall I also grew small fava in a small patch where my chayote is growing now. I did till in everything from that when it was flowering, but I didn't innoculate that either, and figured all I did was enrich the soil with organic material. I am seeing it will all certainly have a cumulative long term benefit, but it's not a magic bullet. But what is?! LOL

Your link reminded me that the nodules aren't little nuggets of nitrogen. They're more like bacteria hotels.
Members of the bean family (legumes) and some other kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacteria. In exchange for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules) in roots where they can exist In a moist environment.

Will it be enough for corn? It depends.........
If your system is balanced there should be enough.

Still working on that. I did have my own compost for the beds, but everything else in it is commercial bagged stuff (a mix of Kellogg organic potting soils, peat, perlite, and native sand). I know it will be better next year and the year after that....

Thanks to the seeds you planted, I found my answer (not the one I wanted!)
"Cover crop roots contribute only a small amount of PAN for the following crop and are ignored in calculations"
....
"Cover crop N uptake is the total amount of N present in above-ground biomass. Usually, less than half of cover crop N uptake is released as PAN during the first year after incorporation"
Estimating plant-available nitrogen release from cover crops, D.M. Sullivan and N.D. Andrews
https://ir.library.oregonstate.edu/xmlui ... pnw636.pdf

This was also a neat link, and one I'll play with one day when I'm bored, but I don't feel like converting acreage down to 24 square feet right now! A tool for calculating the approximate amount of nitrogen, phosphorus, and potassium that is removed by the harvest of agricultural crops.
https://www.plants.usda.gov/npk/main

I ate all the yummy peas.... and I let them grow to wilting. So, nodules or not, I am not going to get a lot of N back from this, at least not in time for the corn.

[imafan26]

I worked on cover crops before, it has never provided enough nitrogen. It takes approximately three years from the time you get a divorce from synthetics and convert to organics to get organically grown crop to produce as well or get as big as a synthetically fertilized one. Before anyone gasps, there are benefits to going organic even in the first year. While the plants may not be as big and not as productive as the ones grown conventionally, they seem to be much healthier and more disease resistant since they do not put on a lot of new growth so fast as to attract pests.

Synthetic fertilizers do not feed the soil, however I disagree that they really kill organisms if they are not abused.

Organic matter feeds the soil web and it is ultimately the plants, animals, and microorganisms in the ecosystem....their life, function, and death that in the end establishes balance in the system. Imbalances are usually caused by man. It seems the humans in their efforts to increase one side of the equation always forgets that something else must also be changing as a counterbalance.

Humans are in love with monoculture. They replace prairies filled with grasses, weeds, flowers, animals tiny, small and big with a single crop and continuously grow the same crop on the land year after year. Nature never intended for that to happen. Even a forest eventually burns down as has to start over from the ashes.

Animals instead of roaming free, are confined on farms where waste management can become an issue, all that nitrogen in animal wastes if not spread around and there aren't enough plants or animals to consume or convert it, eventually spills over into the water systems causing contamination. So, synthetics are not the only risks to the ecosystem. Even organic compounds and farming methods can become issues when they fence in nature. In the case of dairy farm manure it is too much nitrogen in the form of manure concentrated on the land and not enough on the other side of the scale to keep it in balance.

https://www.soilfoodwebnewyork.com/
https://www.ecoversity.org/archives/soil_ecology.pdf

[applestar]

Here's a thought. ...but I guess we have to factor in imafan's 3 years to convert to organic practices comment because I've been strictly non-chem organic no till blah blah for a very long time -- at least 15 years probably more like 20. But then I live in a suburban development so there is probably a lot of outside influences that creep in despite all my efforts. So less actual organic practices than a large scale farmland using these methods.

But in my tiny pocket -- and it truly is tiny -- "cover crop" doesn't mean a solid cover of them but more like interspersed. All in all the science of it, the published research etc. doesn't apply so directly, but what I've noticed is that even without the larger farm animals -- or maybe because of the lack, I end up "herding" the smaller "livestock".

Earthworms are abundant in my garden soil, not because I import masses of them with manure, etc. So far, I haven't been able to come up with a way to bring manure in --- only newcomers are occasional leftover fishing bait... How many is that? -- but because they grow and reproduce here. They cavort in roots -- I read that they enjoy the root exudates -- legumes with or without nodules seem to attract them. There are more of them when soil is disturbed. They like root zones of weeds like chickweed.

I took a picture -- I'll post it if. I can find it -- in the morning, the surface of the soil in the garden is always lumpy and full of tiny holes especially this time of the year in spring before the summer heat and drought. Fresh mounds of EWC every single morning -- a thin powdery dusting if allowed to dry and were smoothed/spread out, but imagine spreading this every day yourself. That has to add up somehow, right?

I brew AACT and spray and soil drench several times during the growing season -- not strictly regimented -- maybe once or twice a month. Millions of microbes....

Then the birds that criss cross in the air and on the ground, and they leave their deposits. I have moles and chipmunks, and there is a little bunny running loose in the garden mostly spending his time in one area INCLUDING the garden beds (and eating sprouted bean seedlings....). Well that last one is not intentional, but they all leave their little presents.

In addition to the "cover crop" there are other crop residues left on the ground as mulch or put in the compost pile that eventually are returned, cut off weed and grass clipping mulches... Those are my nitrogen sources too.

I do occasionally use purchased organic fertilizer, especially on heavy feeders, in addition to planting legumes in the preceding succession.

It's hard to quantify all that, you know?