Leaving legume roots in the soil

[redser]

Hi, I've read conflicting opinions on this. Leaving the rootballs in the soil is good because of the nitrogen nodules etc. Others saying dig them out as it's good cleanliness practice for desease etc.
I just cleared out some early mangetout plants in the tunnel and I want to put in new ones that I have ready in root trainers. I know I should rotate but I guess as it is in the same growing season it's probably ok. So I'm wondering what you do? Do you leave legume roots in the soil to rot and add nitrogen?
Cheers

[rustylady]

Pull them up and put them on the compost heap.

[Kaiya]

Apparently the nitrogen thing is only true if you cut the plants down before the flower/pod - otherwise the nitrogen goes into the pod. If you pull them up you loosen the soil. If you leave them in they'll rot down, opening up the soil also. Swings and roundabouts. I don't think legumes have many soil borne issues so I would think either way you'd be alright re: rotation.

[VirginVegGrower]

Think Two Sheds said it was proven NOT to leave the nitrogen in the soil, so on her advice I'm pulling mine this year.

[chris]

IIRC TS said, or maybe it was Snadger that nitrogen fixing plants fix nitrogen for their own use, rather than whatever comes along next

Kind of makes sense!

[redser]

Thanks. I'll take them out so.

[scarletrunner]

As said previously,leaving them in gives little or no benefit.

[lukens]

There's more about it here, bottom right of page 2:

http://aces.nmsu.edu/pubs/_a/a-129.pdf


Copy/pasted for convenience:

The amount of nitrogen returned to the soil during or after a legume crop can be misleading. Almost all of the nitrogen fixed goes directly into the plant. Little leaks into the soil for a neighboring nonlegume plant. However, nitrogen eventually returns to the soil for a neighboring plant when vegetation (roots, leaves, fruits) of the legume dies and decomposes.

When the grain from a grain legume crop is harvested, little nitrogen is returned for the following crop. Most of the nitrogen fixed during the season is removed from the field. The stalks, leaves and roots of grain legumes, such as soybeans and beans contain about the same concentration of nitrogen as found in non-legume crop residue. In fact, the residue from a corn crop contains more nitrogen than the residue from a bean crop, simply because the corn crop has more residue.

A perennial or forage legume crop only adds significant nitrogen for the following crop if the entire biomass (stems, leaves, roots) is incorporated into the soil. If a forage is cut and removed from the field, most of the nitrogen fixed by the forage is removed. Roots and crowns add little soil nitrogen compared with the aboveground biomass.

[Two_Sheds]

Leaving the rootballs in the soil is good because of the nitrogen nodules

That's old advice: it's since been disproven (although the old advice still gets quoted)

Think Two Sheds said it was proven NOT to leave the nitrogen in the soil

Not just me, others have too, Zazen amongst them

http://www.growfruitandveg.co.uk/gra...ing_54424.html

[solway cropper]

All the studies I've seen for commercial agriculture seem to say that the entire plant should be ploughed in and then there may be a useful addition of nitrogen to the soil, but then if the crop was buttercups and you ploughed the entire lot in there would still be a benefit. Some leguminous plants appear to offer a significant addition of nitrogen to the soil but this is only when comparing the cost of the seed, etc. to the cost of ammonium nitrate fertilizer. For the home grower I'd say the benefit ranged from non to negligible.

But to the original question, I just pull em up and put em on the compost heap.

[Two_Sheds]

Some leguminous plants appear to offer a significant addition of nitrogen to the soil

I'm growing alfalfa as a perennial in amongst my veggies. I cut it several times a year, just leaving the bits on the surface ~ they soon get absorbed into the soil.

I find it really easy and am very impressed with the improvement, esp. at school: there was one bed that wouldn't even grow weeds it was so poor, but now it's got all kinds of pretties in it.

I was inspired to do it by One Straw Revolution (a Japanese farmer who doesn't make compost, he just chucks the dead crops straight onto the soil and plants through them). I'm doing the same with weeds now ~ just chop them up and leave them on the soil as a mulch

[redser]

Thanks for that TS. I only have room for 2 daleks on my small plot so now I know what to do with excess material