When is legume fixated nitrogen available?

[Steve Wilson]

I read a university study somewhere that stated that clover, seeded at 5 to 6 pounds per acre, is able to fixate up to 150 pounds of nitrogen per year. Ok, let's agree that study was likely based on ideal conditions and we would be lucky to get half that much. Still, given the high cost of fertilizer these days, it seems to me that a person needs to start considering planting lots of clover. Not to mention the increased forage value clover adds.

Does anyone have any data, or idea, of when the nitrogen becomes available to the grasses? Is it when the rootlet that has the nitrogen nodules dies?

Thanks,

 

[dun]

Does anyone have any data, or idea, of when the nitrogen becomes available to the grasses? Is it when the rootlet that has the nitrogen nodules dies?

Thanks,

That's what I was taught

 

[JRM]

Good question.
I asked an "expert" and from I got from him is that most of the nitrogen is returned to the soil when a cow eats the legume and is passed through the cow back to the soil. He said a little would be put in the soil through nodules.
I was asking him about using clover in a hay field and he felt that clover in a hay field would not prove much nitrogen to the soil, but would help the hay and provide nitrogen back into the pasture.
I still have allot of questions about clover/legumes. I know it helps my pasture, but would like to know when and how the clover/legume benefits the soil. Cows really love it.

 

[Jogeephus]

Don't know if this is right but I was told by another "expert" that if you keep clover on the site the dying plants will release the N gradually and that if you maintain good stands of clover you can reduce your N application by 30%.

 

[MrBilly]

There are many articles that explain how the N is made by clover. Below is a simple explanation. It is NOT by cows eating the clover and then pooping the N back to the soil, but N is generated by bacteria in nodules on the roots of clover where the N is directly made and placed right in the soil for use by the clover and adjacent plants.

Billy


http://www.independent.ie/farming/clove ... 67487.html

 

[dun]

Extract from: http://overton.tamu.edu/clover/cool/nfix.htm
Emphasis is mine.

A common misconception is that the nitrogen is released into the soil from the legume roots. Research has shown there is a release of some soluble nitrogen compounds such as amino acids and ammonium from intact legume roots and nodules, but it is an insignificant amount. The primary pathways for nitrogen transfer from the legume to the soil are through grazing livestock and decomposition of dead legume plant material. When legume forage is consumed by grazing livestock, from 80 to 90% of the nitrogen in that forage passes through the animal and is excreted in the urine and feces. Unfortunately about 50% of the nitrogen in the urine is lost through volatilization. Another problem is the distribution of feces and urine on the pasture. With continuous grazing at low stocking rates, much of the animal excreta is concentrated around the water source and under shade trees. Animal excreta distribution is improved with moderate to high stocking rates and with rotational grazing systems where stock density is higher.

The root system and unused leaves and stems of annual legumes die at plant maturity and are decomposed by soil microbes over time. Nitrogen contained in this plant material is released over time and is available to other plants. However, because most of this nitrogen is not available until after the legume dies, only grasses that follow the legume growing season can use it. This is a major nitrogen transfer pathway for cool-season annual legumes overseeded on warm-season perennial grasses because the clover-growing period occurs before the warm-season grass-growing period.

 

[MikeC]

Have seen "Green Manure" crops, especially Vetch with excellent results, planteIn agriculture, a green manure is a type of cover crop grown primarily to add nutrients and organic matter to the soil.


Typically, a green manure crop is grown for a specific period, and then plowed under and incorporated into the soil. Green manures usually perform multiple functions, that include soil improvement and soil protection:

Leguminous green manures such as clover and vetch contain nitrogen-fixing symbiotic bacteria in root nodules that fix atmospheric nitrogen in a form that plants can use.
Green manures increase the percentage of organic matter (biomass) in the soil, thereby improving water retention, aeration, and other soil characteristics.
The root systems of some varieties of green manure grow deep in the soil and bring up nutrient resources unavailable to shallower-rooted crops.
Common cover crop functions of weed suppression and prevention of soil erosion and compaction are often also taken into account when selecting and using green manures.
Some green manure crops, when allowed to flower, provide forage for pollinating insects.
Historically, the practice of green manuring can be traced back to the fallow cycle of crop rotation, which was used to allow soils to recover.

 

[Horse Guy]

I find this thread extremely interesting.
All I can add is that I was told by a farmer friend that years ago it was common around here for people to grow a crop of clover and then to just plow the whole crop under for fertilizer.Course gas and diesel wasnt much of an issue years ago like today.
I know with myself this year I did nothing. One of my stands of alfalfa is eleven years old and it hasnt been fertilized for going on 4 years now. Heck its doing great so far! Ive got just as much as anyone and more than most so far but I know im eventually going to have to do something with it.

 

[Horse Guy]

Here is a good link
http://www1.agric.gov.ab.ca/$department ... endocument
and
http://www1.agric.gov.ab.ca/$department ... ll/faq7979

 

[PJungnitsch]

Grazing would be the best way to get N from the legume back into the grass IMO. A cow keeps only 10% of the N, and 3/4 of what comes out the back is urea nitrogen in the urine, 46-0-0 in water.

So the cow is a liquid N fertilizer factory, as mentioned the trick is to keep them applying it evenly, and not letting them dump that fertilizer in the trees, around the waterer, etc. Plus the less bare ground, the more gets captured, but still it's free commercial fertilizer N that the you are harvesting from the mini N factories working hard in the roots of every clover/alfalfa plant.

Growing up we used to have alfalfa/clovers in the rotation especially to build up our grey wooded soil, and always saw a big response after it had rotted down for a couple years, but there was a lot of plowing involved. Easier to let the cow do the work.

The cows are also dumping a lot of potassium and some phosphorus at the same time (as well as sulphur, calcium, magnesium, etc), and I'm starting to think that might be a really good thing for keeping legumes healthy in the long run.

 

[The Bachelor]

You know I was watching the Hefty brothers talking about the nodules storing up nitrogen until the beanhead formed (on soybeans), then the nitrogen was transfered up to the bean. I wonder if clover does the same thing when it flowers? Any Thoughts?

 

[alabama]

You know I was watching the Hefty brothers talking about the nodules storing up nitrogen until the beanhead formed (on soybeans), then the nitrogen was transfered up to the bean. I wonder if clover does the same thing when it flowers? Any Thoughts?

This is a great topic and I wish we could get some good answers form some of our university professors.
I have always thought that the nodules on the root were kind of like time release fertilizer granules that released N as they degraded.

 

[MrBilly]

I think we are all correct to a point. Indeed when cattle consume legumes and poop out the digested materials there is some transfer of the nitrogen back to the soil in this manner - how much is unclear. The good news is that the animal can transport the N from one spot to another far away.

However, the bacteria in the root nodules is the main factory for N production through the N fixation process. The nodules go through a cycle of life, as they grow older, they slough off, decompose right there next to the roots, release their stored nitrogen into the soil that is then used by the legume and the associated grasses (from "Southern Forages" by Ball, Hoveland and Lacefield).

I have not found a specific percentage, but I will try to find it from our forage professors.

Billy

 

[dun]

To me one of the sure fire indicators of lack of N is when there are darker green spots in the pasture where a cow has peed

 

[SRBeef]

It has long been the practice when figuring the fertilizer needs of a corn crop to make an N allowance if the previous crop was soybeans, another legume. Soybeans are innoculate with the bacteria that encourage formation of the root nodules where much of the N is either producer or stored. Beans planted in ground which has not had beans in it before and which were not innoculated have few or no root nodules and will produce little or no residual N.

I'm not sure of the soybean bu/acre yield vs pounds of N credit for the following crop. However it is not unusual to reduce N application by 50-60 lbs N (the N credit) per acre for a corn crop when the previous crop was soybeans.

Soybeans planted into a killed clover crop should also get some N credit from the root nodules.

I believe much of the N fixed by the root nodules is available the following season for other non legume crops with roots in the area of the nodules.

There is N deposited in the manure and urine of cattle even when they are on a non-legume feed such as grass hay probably not as much as when they are on a higher percent of clover or alfalfa. I think there is some point in a stand where we need to watch out for bloat in a pure stand of alfalfa or clover...they need some grass etc in there with the legume.