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Old 19-09-2003, 03:42 PM
Phred
 
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Default Nitrogen-fixing crops.

"BGGS" wrote in message ...
I was under the impression that nitrogen-fixing crops were a good thing
until a few weeks ago I heard two farmers discussing on radio how "growing
beans makes a mess of the soil and removes the nutrients".


When you say "beans", do you mean soy[a]beans?

When I shouted myself a trip around the US a few decades ago, I learnt
that soyabeans are typically "parasitic" on soil N in spite of their
ability to fix atmospheric N through their root nodule bacteria. In
other words, the yield of N in a crop was greater than the amount
fixed. I have to say I was a bit surprised by this outcome too,
because I had been well indoctrinated with the "legume/rhizobium
symbiosis" as an undergraduate.

This effect may well depend on the native N in the soil initially.
The more "naturally" available, the less efficient the RNB association
is likely to be. Certainly, the application of bag N typically
reduces the amount fixed (and is a common means of removing unwanted
legumes from domestic lawns here).

There are other issues too. Most obviously, growing any
harvestable crop will deplete soil nutrients. While legumes may
even be able to increase soil N levels in some circumstances, there
will still be a nett loss of things like P and K if they are harvested
and removed from the field. Indeed, most of the N will usually be
removed too if the crop is to have any value elsewhere.

Another aspect relating to your "makes a mess of the soil" is that
legume crops typically involve more cultivation and chemical
treatments than many broadacre gramineous crops. Their root system is
also inferior to the fibrous roots of grasses in preserving
soil structure (at least that's what I was taught many years ago .

I'd like to know how the two things can be true. I'm aware of the
root-nodules on bean plants so they certainly do fix their own N so why
would they not be a desirable crop ?

In Japanese agriculture of the Eddo period and possibly earlier, farmers
were required by quite rigid rules to grow rice in the middle of the field
and beans around the edges to shelter it and provide the soil with nutrients
so it must work.


Yes. I believe soyabeans have been used this way for centuries. They
are very well adapted to the system, which may be one reason why they
are not so efficient as N fixers in conventional agriculture. Indeed,
their ability to tolerate wet soil is one reason they are now being
used as a green manure crop for rotation with sugar cane in the wet
tropical lowlands around here.

I don't hear about crops being combined today outside of some rotation
systems even though this method makes run-off problems non-existent.
Is it perhaps because the natural fixing-qualities of bean plants is fairly
feeble compared to present-day fertilizers?


Some can fix quite large amounts of N. But to take advantage of it,
you really need to plough the lot in. If you harvest for pulse, hay,
whatever, you'll most likely remove most of the N that was fixed.


Cheers, Phred.

--
LID


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Old 19-09-2003, 04:02 PM
P van Rijckevorsel
 
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Default Nitrogen-fixing crops.

Phred schreef
In other words, the yield of N in a crop was greater than the amount
fixed.


Indeed, most of the N will usually be
removed too if the crop is to have any value elsewhere.


If you harvest for pulse, hay,
whatever, you'll most likely remove most of the N that was fixed.


+ + +
I suppose this is even more true for soybeans which, after all, are grown as
a protein source, preferred because of its high protein content. It is not
like it is rice.
PvR


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Old 20-09-2003, 04:20 AM
Dean Hoffman
 
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Default Nitrogen-fixing crops.

On 9/19/03 9:38 AM, in article ,
"Phred" wrote:


When I shouted myself a trip around the US a few decades ago, I learnt
that soyabeans are typically "parasitic" on soil N in spite of their
ability to fix atmospheric N through their root nodule bacteria. In
other words, the yield of N in a crop was greater than the amount
fixed. I have to say I was a bit surprised by this outcome too,
because I had been well indoctrinated with the "legume/rhizobium
symbiosis" as an undergraduate.


For whatever it's worth, here's a chart showing the contributions of
legumes to the next year's corn crop. The chart is about 1/2 way down on
the right side.

http://www.ianr.unl.edu/pubs/fieldcrops/g174.htm

The research is from the University of Nebraska at Lincoln. The
Nebguides are recommendations to farmers for crop production.


Some cut.

Another aspect relating to your "makes a mess of the soil" is that
legume crops typically involve more cultivation and chemical
treatments than many broadacre gramineous crops. Their root system is
also inferior to the fibrous roots of grasses in preserving
soil structure (at least that's what I was taught many years ago .


No till and roundup ready soybeans are really changing farming practices.
Beans are sometimes drilled directly into the previous year's crop residue.
They're sprayed for weed control. Farmers in my area of Nebraska, USA are
really cutting back on the tillage. It's just too expensive to cultivate
unless absolutely necessary.
Some farmers here plant the corn, cultivate maybe once, and then spray to
control the weeds.

Cut rest.

Dean



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Old 20-09-2003, 08:12 AM
BGGS
 
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Default Nitrogen-fixing crops.


"Dean Hoffman" wrote in message
...
On 9/19/03 9:38 AM, in article

,
"Phred" wrote:


When I shouted myself a trip around the US a few decades ago, I learnt
that soyabeans are typically "parasitic" on soil N in spite of their
ability to fix atmospheric N through their root nodule bacteria. In
other words, the yield of N in a crop was greater than the amount
fixed. I have to say I was a bit surprised by this outcome too,
because I had been well indoctrinated with the "legume/rhizobium
symbiosis" as an undergraduate.


For whatever it's worth, here's a chart showing the contributions of
legumes to the next year's corn crop. The chart is about 1/2 way down on
the right side.

http://www.ianr.unl.edu/pubs/fieldcrops/g174.htm

The research is from the University of Nebraska at Lincoln. The
Nebguides are recommendations to farmers for crop production.


Some cut.

Another aspect relating to your "makes a mess of the soil" is that
legume crops typically involve more cultivation and chemical
treatments than many broadacre gramineous crops. Their root system is
also inferior to the fibrous roots of grasses in preserving
soil structure (at least that's what I was taught many years ago .


No till and roundup ready soybeans are really changing farming

practices.
Beans are sometimes drilled directly into the previous year's crop

residue.
They're sprayed for weed control. Farmers in my area of Nebraska, USA are
really cutting back on the tillage. It's just too expensive to cultivate
unless absolutely necessary.
Some farmers here plant the corn, cultivate maybe once, and then spray

to
control the weeds.

Cut rest.

Dean


Thanks for that, Dean.
Do you ever hear of anyone using the "Sweet plough"? ("Sweet plow"?)
It was developed with the intention of skimming the roots off the weeds but
leaving the surface detritus (litter) untouched to prevent erosion. It helps
to preserve the soil structure by leaving the roots from the previous crop
in situ.
It consists of a pair of wings (horizontal blades) attached to the vertical
blade.
Always thought it a damn good idea, but like all good ideas.....
"Roundup ready" soybeans sound like a Monsanto GM product. There's
tremendous opposition to them here in the UK. I've never seen so many people
so highly motivated.
Barley is very important here. Wonderful crop.
Thanks
BG.




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Old 20-09-2003, 03:02 PM
Dean Hoffman
 
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Default Nitrogen-fixing crops.

On 9/20/03 2:01 AM, in article ,
"BGGS" wrote:

Thanks for that, Dean.
Do you ever hear of anyone using the "Sweet plough"? ("Sweet plow"?)
It was developed with the intention of skimming the roots off the weeds but
leaving the surface detritus (litter) untouched to prevent erosion. It helps
to preserve the soil structure by leaving the roots from the previous crop
in situ.
It consists of a pair of wings (horizontal blades) attached to the vertical
blade.
Always thought it a damn good idea, but like all good ideas.....
"Roundup ready" soybeans sound like a Monsanto GM product. There's
tremendous opposition to them here in the UK. I've never seen so many people
so highly motivated.
Barley is very important here. Wonderful crop.
Thanks
BG.


There's a variety of schemes.

http://www.cedarmeadowfarm.com/TFSArticle05.html

These choppers were used years ago. They're getting more popular again
for corn and soybean farmers. The practice here is to chop the stalks with
one tractor and then plant right away with another tractor.
There are a variety of no till or ridge till units that can mount directly
in front of the planter unit. That allows one operator to do the planting.
One uses a vertical disc followed by a horizontal one to clear the top of
the ridge. Others use two discs angled just slightly off the vertical. The
trash is just pushed off the top of the ridge. Hiniker and Buffalo are two
brand names of these units. I think Buffalo (Fleisher Manufacturing) was
the first with the no/ridge till units.
No till drills are also getting more popular for soybeans. There isn't
much wheat, oats or barley in my area so I can't say what current practices
are for those crops.
Wheat farmers in dryer areas used something called a rod weeder. I don't
remember what they looked like. There's also something called a duckfoot.
That's just a rig with very wide sweeps. Think of a horizontal V pulled
just below the soil surface. I think the open end of the V was maybe 3'
wide.
I tried to find some pictures of this stuff but a brief search didn't
turn up any good ones. There's all kinds of information on ridge till and
no till farming practices from the University of Nebraska and similar
institutions in the U.S.

Dean




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