Whoa buddy, I just came into this forum to find out this very thing!! TY TY TY If my question isn't answered, I'll be back. :)

just one thing I haven't found an answer to. How long does N stay in the soil? I am trying to revamp an old heavy clay flower bed. After research on these forums I found that organic matter and mulch are the answer. So, I planted bagged grocery store cowpeas thinking that the N would still be in the soil next spring. My plan is to turn all plant residue into the soil and lay several inches of shredded leaves on top. But then, I read that the N leaches out of soil.. Im assuming by soil erosion? Guess I"m confused about whether it was worth it to plant/turn under and leaf mulch the peas. For some reason, the Soil Food Web is hard for me to grasp. Thank you

Hi Jim,
It is good info. link for gardeners.Thanks for intro.I GOOGLed to get more info. about N(nitrogen) fixation.It is the total mass,roots,leaves and stems of the plants(legums) that will enrich the soil with N.

sudzy, it is difficult to predict how long the soil will retain N.Erosion, type and location of the soil will be the controlling factors for this.I came across some references that will recommend to plant perennial legums by late summer to reduce erosion of N.Root system of perennial legumes will penetrate deeper in the soil,little difficult to be eroded.Secondly these legumes can be cultivated (by tilling or ploughing) in the soil with entire mass of the plants.This process will bring N nodules on the roots to the soil saurface for biodegradation.

Don't confuse leeching and erosion. Leeching is when soluble elements are washed out of the soil by water percolating through. Erosion is removal of soil when soil particles are transported away by runoff of water.

My soil is more sand than anything else. Leeching is a problem here because water penetrates through so quickly and the soil has only a small amount of humus and practically no clay. Humus and clay both will trap and retain nutrients (such as nitrogen).

Clay soil may have its drawbacks, but it has the ability to hold water and nutrients. Adding compost will help your soil and mine too.

The big question I had which caused me to seek out the information is "at what point do legumes start using the nitrogen they fix?". The answer turned out to be that they begin to benefit from their own nitrogen fixation within the first two or three weeks of planting (prior to which they may have a nitrogen deficit as indicated by yellow leaves) and it continues until pod fill. So a legume does benefit from its nitrogen fixation during its own lifetime. Other plants benefit later, when the legume dies and becomes part of the soil.

It was also interesting to find that "Common beans are poor fixers (less than 50 lbs per acre) and fix less than their nitrogen needs." This answers a question from another thread about whether or not to fertilize beans.

Jim

Great site jim I have bookmarked it. On how long Nitrogen last. I will say it is short lived once it is in a form usable by the plant. That is why when a soil test is performed it is never analyzed for N due to its short presence and high leechability in soil especially sandy soils. My literature on cover crops for soil fertility state legume crops such as field peas alfalfa and clovers should be turned under at begining on bloom prior to pod set for maximum N addition and the Nitrogen is a slow release nitrogen over 60-90days as the nodules break down and the nitrogen is converted into a usable form. Commercial N is only avaiable for 2-3 weeks in average soils due to leaching which is why a lot of University fertilizing guidlines suggest side dressing with nitrogen on heavy feeding crops such as corn about a month after planting.

On the fact that common beans are poor fixers is a reason why I don't believe it is necessary to use inoculants on them and to only use innoculants if the legume is being used as a cover crop. So if field peas are grown for consumption no need to use innoculant and no need to add nitrogen, if field peas used to increase soil fertility and will be turned under at begining of pod and bloom set use an inoculant to get the most N out of the crop. Rodger

Interesting subject. My son found out my interest in N and plants and went to his room. He returned with a textbook from his college bio class last year, Plants and Society which he tossed in my lap!. Whooho. This will keep me busy reading.
There is a chapter on Nitrogen-Fixing of Legumes with a picture of the nodules on plant roots. So, I pulled two cowpea plants to see if they had any. These plants are in the bloom stage. Neither had the nodules and I THINK I should've been able to see them with the naked eye. Please correct me if I'm wrong on that.
Thanks for all the good info in this thread.

"My son found out my interest in N and plants and..."

Kids are great...

You say you "pulled" two plants. Did you mean that literally? Could it be that pulling plants could strip off the nodules? Maybe try carefully excavating.

Hey, wait! I have my own cowpeas I could check. Also several other beans. I used no inoculant.

Jim

Here's a picture of a Butterbean root showing nodules I took a couple of years ago.

wow, the nodules are large. Thanks. Going out in the a.m to redo my cowpea experiment. Going to gently dig them up this time. Gonna check out my bush beans too.
Roger did you use an inoculant on those butter beans?

BTW, I have no idea if it is possible to strip off the nodules by pulling the plant. I never tried it. I never dug them either. It was just a thought and, for all I know, the nodules are an integral part of the root. We shall see.

Jim

When I inoculated yardlongs (which are just climbing cowpeas), they developed numerous large nodules, 1/8-1/4" wide. These are the largest nodules I've seen on any legume I have grown. The article posted by Jimster finally explains what I have noticed in my own investigations... nodules seem relatively scarce on beans. Here I thought I was just digging them up too roughly - we had the same thought, Jimster.

Rodger, I love ya man, you are one of my bean gurus... but I'm not sure those are nitrogen-fixing nodules on your beans. Have you cut one open, to view the interior? From the photo, it appears more like the galls produced by root knot nematodes, which are endemic to warm-climate areas.

Zeedman, you could be right, I have not cut them open and assumed they were nodules. That picture was taken a couple of years ago. The only thing odd would be I have not seen the galls on other plants that are bothered by root knot nematodes such as cole crops. I have not dug peas to check for nodules. I have seen 1/4 inch size nodules on p-nuts when they are dug.I noticed the nodules on the Butterbeans while pulling up the vines to remove the poles. There were no nodules on the common beans and usually I don't need to pull up the vines on the common beans to remove the poles. The common bean vines decay quickly and easily slip off. The pea vines since there are no poles are just tilled under so I have not looked for them. I have always noted very large and vigorous roots on Limas with those large galls. Looks like I have a mission for this fall. Rodger

Jimster-- your instinct was right. The little nodules can come right off. Easily.

Cowpeas--No nodules. These came from grocery store in a 14 bean bag for soup. Perhaps something in the preservation for consumption???

Fava beans that I planted much earlier in the season did have nodules. Can't share a pic. Digital camera is broken

Three days ago I had cut my Top Crop bush green beans down to the soil line and covered with mulch. I dug up a couple and no nodules. I would not think it would be decomposition already. But I don't know.
Totally unscientific results. But it was fun!. :)

Roots of peanut plants provide good example of N nodules.Pull out the plants when leaves start yellowing.You will find rows of white nodules on the roots.If the plant is older nodules will be brownish red (in light color).

You know, I've been wanting to try peanuts in Wisconsin, just for the challenge. Maybe next year, if I have a normal Spring!

It has been four years almost to the day since this thread was initiated and I just rediscovered the site which was linked in the initial post and which I had forgotten in the mean time. Events in my garden caused me to search for inform on nitrogen and beans. The information in the linked article provided exactly the information I needed.

Jim

Here is a link that might be useful: Nitrogen Fixation By Legumes