Legumes & nitrogen

[dun]

There has in the past been discussions about clover, etc. and it's nitrogen producing/fixing qualitys. The proper inoculant is required but when is the nitrogen made available to the other plants?

 

[plumber_greg]

Dun, I bought in to Gerrish's theories one year of 5lbs. red clover and mig replacing fertilizer needs. The main trouble I had the one year I tried it was that we ususally turn out last week of April, and it was a little dry that spring and I had no grass. Slapped some nitrogen down, had little shower and the grass came on. I think if you want to depend on clovers for nitrogen, it may work in a hayfield, but pastures still need the early spring push. Do you remember the experiment MU ran about cows needing no shade? A 40 percent conception rate on black cows killed that one. gs

 

[dun]

Dun, I bought in to Gerrish's theories one year of 5lbs. red clover and mig replacing fertilizer needs. The main trouble I had the one year I tried it was that we ususally turn out last week of April, and it was a little dry that spring and I had no grass. Slapped some nitrogen down, had little shower and the grass came on. I think if you want to depend on clovers for nitrogen, it may work in a hayfield, but pastures still need the early spring push. Do you remember the experiment MU ran about cows needing no shade? A 40 percent conception rate on black cows killed that one. gs

Our pastures rarely need any nitrogen. Maybe it's from the clover or maybe it's just pasture rotations puts most of it back on the ground. Our hay fields are the places we have to use nitrogen every other year or so. Haying mines nutrients

 

[novatech]

There has in the past been discussions about clover, etc. and it's nitrogen producing/fixing qualitys. The proper inoculant is required but when is the nitrogen made available to the other plants?

Some N is available from the nodules. The majority is from the foliage. After decomposition of the leaf and stem (mowing or death of plant) in the ground it becomes available. The other way is through fecal mater decomposing in the ground. Microorganisms needed to produce nodules (inoculate). Then more Microorganisms to convert the forage or fecal mater into usable food for the other plants.

PS
Something else I would like to add. The fact that you have clover does not necessarily mean it is fixing Nitrogen. Legumes are like any other plant. The lack of certain requirements may reduce the ability of the clover to fix the N. proper PH is essential. Phosphorous and potash along with micronutrients must be available. In the early stages of growth legumes can use a certain amount of N. It must use up the N before it can produce any more which is what happen in the mature stage. Allowing it to mature and seed out will produce the most Nitrogen fixation and provide seed for the next years season.
To see if you are getting the nitrogen fixation, dig up the clover root and inspect the nodules. If they are pink they are fixing. You may have to cut the nodules open in some clovers.

 

[fargus]

A lot of the N will be made available by the cow. If 80% of what she takes in goes back out, then the urine is the primary way for the N from clovers to become available to other plants. I've seen one study that suggests there is a certain amount of "direct mychorhizal transfer" from roots/nodules of legumes to the roots of grass species. (That being said, I've only seen the one study, and the results were far from consistent.)

As nova mentioned, the breakdown of the leaf litter and root material that has died off will provide up to 100 lbs/ac of N recycling in any given year.

 

[Stocker Steve]

I think there are a couple drawbacks to not applying N. N is not available when soil is cold in spring or fall, and some grasses are heavy users of N. I usually put on 40# per acre as soon as I can drive on sod, and consider a second application on anything I stockpile in the fall.

The mob grazing guys brag about how they increase the organic matter a couple percent in one year, but I do not understand how that is possible :???: I realize they are putting more litter on the ground (due to lower forage utilization) compared to someone who is grazing at a shorter height...

Have you seen any believable soil test data on mob grazed ground?

 

[fargus]

Can't say as I've seen any good soil test data from the mob grazing crowd. My uncle is Ontario's soil fertility specialist, and this is usually what he says about OM: "The fastest way to increase your soils OM test by 1% is to lie about it."

 

[novatech]

I think there are a couple drawbacks to not applying N. N is not available when soil is cold in spring or fall, and some grasses are heavy users of N. I usually put on 40# per acre as soon as I can drive on sod, and consider a second application on anything I stockpile in the fall.

The mob grazing guys brag about how they increase the organic matter a couple percent in one year, but I do not understand how that is possible :???: I realize they are putting more litter on the ground (due to lower forage utilization) compared to someone who is grazing at a shorter height...


The theory is that if you allow the grass to get close to maturity in height and only graze it down by 40 or 50% then the root system is not hurt and allows the grass to grow faster. When grasses are grazed short the root system responds equally, it too is short, therefore the grass grows slower plus the fact that they will not have the depth to pick up the nutrients and water necessary throughout the seasons. There is not enough leaf to shade the soil and no thatch to feed the microorganisms.[/color]

Have you seen any believable soil test data on mob grazed ground?

I am not a mob grazer nor do I practice any form of intensive grazing as far as rotation. What I do is watch their methods, pastures and pasture stocking rates for the proof. I can assure you for those that do it well benefit. I have seen the proof that the intensive grazing works. The soil test is in the stocking rate and the gain per day. So the answer to your question would be yes. Most people get a soil test for only Ph, N P and K. But there is a lot more to soil than that. I think the organic mater increase is a lot more than 1 or 2 % when done properly and that, from what I have gathered, is their biggest benefit. I read an article that said it would take 27 years of cattle being on open pasture to totally cover all spots in the pasture with manure. With intensive grazing it is done in a couple of years. The organic matter along with the microbes allow the pasture grasses to take up the fertilizer. It makes it available to the plant.
(due to lower forage utilization)

 

[fargus]

I have heard about the study that talks about pasture coverage by cattle manure. We intensively graze, and get the benefits of increased stocking rate, better production during drought, etc.

Keep in mind, that an acre furrow slice (6" of topsoil on 43,560 square feet) is somewhere in the neighbourhood of 2 MILLION pounds. To raise your OM test 1% that is 20,000 lbs of extra residue LEFT. That is similar to growing a phenomenal crop of Winter Wheat (about 100 bu/ac or better) incorporating all of the grain and the straw, and losing none of the carbon. (It would all have to be assimilated into the soil carbon pool.) You aren't gonna do that in just a year. I apologize if my math is a bit rough, those numbers are all off the top of my head.

 

[JRGidaho`]

I'd have to say all the comments above concerning when and how N becomes available from legumes are accurate.

1) As soon as N-fixation begins, there is some leakage from the nodules. Not a big contribution in the first few months of growth, but significant in older stands.
2) As forage is eaten, some N returns rapidly as urine and more slowly as dung. A significant contribution as long as ammonia volatalization is not excessive.
3) If the grazing is severe, the plant will jettison some nodules and the slow release through decomposition begins. A steady contributor over time.
4) As legumes die (short lived red clover, annual clovers or vetch, etc) total plant decompostion contrinutes to soil N pool. A major contributor.
5) Trampled litter with the grazing process. A steady decompostion process. Amount of N directly proportional to amount of plant litter left behind.

Reported levels of N fixation and subsequent contribution to soil N from Iowa State study.

Alflafa 120-230 lb/acre
Red clover 130-250
White clover 20-240
Birdsfoot trefoil 80 - 150

Most of the difference due to stand density. All in all a pretty good contribution of N from legumes.

I have seen very similar numbers from Alberta

 

[JRGidaho`]

Dun, I bought in to Gerrish's theories one year of 5lbs. red clover and mig replacing fertilizer needs. The main trouble I had the one year I tried it was that we ususally turn out last week of April, and it was a little dry that spring and I had no grass. Slapped some nitrogen down, had little shower and the grass came on. I think if you want to depend on clovers for nitrogen, it may work in a hayfield, but pastures still need the early spring push. Do you remember the experiment MU ran about cows needing no shade? A 40 percent conception rate on black cows killed that one. gs

One year trying to do clover instead of N-fertilizer may or may not show anything, depending on the season. It usually takes a few years to build the legume component to the needed level. I've probably mentioned it before, but there were only three occasions in the 22 years we ran cattle and sheep in north MO that we ever used N-fertilizer. We ran a cow-calf equivalent year-around on just over 2 acres of grass-legume pasture.Here in ID we use no N and are harvesting over 300 CDA (or about 5 ton/acre).

On the research study you refer to, it's interesting to note that same cow herd had performed very well with no shade for over 20 years when they calved Feb-March and were bred in May-June. It wasn't until calving was moved to April 15 and breeding didn't start until July that the wreck occurred. The low conception rate was due to near-total bull failure, not cows failing to cycle or settle. The same time they were doing that study, I had red cows about ten miles away calving April 15 to May 30 and breeding in July-August with a consistent 93% breed-up. I'd say it was bad bull selection more than anything in that MU study.

 

[JRGidaho`]

I have heard about the study that talks about pasture coverage by cattle manure. We intensively graze, and get the benefits of increased stocking rate, better production during drought, etc.

Keep in mind, that an acre furrow slice (6" of topsoil on 43,560 square feet) is somewhere in the neighbourhood of 2 MILLION pounds. To raise your OM test 1% that is 20,000 lbs of extra residue LEFT. That is similar to growing a phenomenal crop of Winter Wheat (about 100 bu/ac or better) incorporating all of the grain and the straw, and losing none of the carbon. (It would all have to be assimilated into the soil carbon pool.) You aren't gonna do that in just a year. I apologize if my math is a bit rough, those numbers are all off the top of my head.

fargus, I think your math is correct and the 20,000 lb OM is what would have to be added to raise 1%. Next to impossible to grow 20000 lb forage in most of US & Canada, let alone have that much returned to the soil. When I take soil samples, I always scuff away the debris layer on the soil surface (which really isn't humus yet) and put the probe directly into the mineral soil. If you take a sample punching down through the litter layer, you will get an inflated OM reading.

Another real easy way to double your organic matter is change from taking 6-8" soil cores to just taking 3-4" cores. The lab will still calculate all your analysis based on the 6" plow layer unless you told them it was a shallow sample.

 

[novatech]

I have heard about the study that talks about pasture coverage by cattle manure. We intensively graze, and get the benefits of increased stocking rate, better production during drought, etc.

Keep in mind, that an acre furrow slice (6" of topsoil on 43,560 square feet) is somewhere in the neighbourhood of 2 MILLION pounds. To raise your OM test 1% that is 20,000 lbs of extra residue LEFT. That is similar to growing a phenomenal crop of Winter Wheat (about 100 bu/ac or better) incorporating all of the grain and the straw, and losing none of the carbon. (It would all have to be assimilated into the soil carbon pool.) You aren't gonna do that in just a year. I apologize if my math is a bit rough, those numbers are all off the top of my head.

fargus, I think your math is correct and the 20,000 lb OM is what would have to be added to raise 1%. Next to impossible to grow 20000 lb forage in most of US & Canada, let alone have that much returned to the soil. When I take soil samples, I always scuff away the debris layer on the soil surface (which really isn't humus yet) and put the probe directly into the mineral soil. If you take a sample punching down through the litter layer, you will get an inflated OM reading.

Another real easy way to double your organic matter is change from taking 6-8" soil cores to just taking 3-4" cores. The lab will still calculate all your analysis based on the 6" plow layer unless you told them it was a shallow sample.

I did my own calculations and found I was way wrong. After further research found this article. http://www.soilhealthknowledge.com.au/i ... &Itemid=85

(recent data suggests an additional 2 t/ha of plant residues retained each year for 20 years can increase SOM by only 0.5%).

I think their figures are based on crop removal and not pasture, but it would still fall short of the numbers I posted.
Very good link though.

 

[Stocker Steve]

I think I get it. So I let the forage get taller, flatten it with mob density, take a shallow 3" deep sample including as much litter as possible, and then brag about my OM. ;-)

On a more serious note, one of the reasons given for the typical forage production decline a couple years after tillage - - is that the OM exposed by mechanical tillage has been consumed.

 

[Stocker Steve]

I've probably mentioned it before, but there were only three occasions in the 22 years we ran cattle and sheep in north MO that we ever used N-fertilizer. We ran a cow-calf equivalent year-around on just over 2 acres of grass-legume pasture.Here in ID we use no N and are harvesting over 300 CDA (or about 5 ton/acre).

Is your point that N was not economical most years or that you were understocked or that you had great legume stands?

 

[JRGidaho`]

I've probably mentioned it before, but there were only three occasions in the 22 years we ran cattle and sheep in north MO that we ever used N-fertilizer. We ran a cow-calf equivalent year-around on just over 2 acres of grass-legume pasture.Here in ID we use no N and are harvesting over 300 CDA (or about 5 ton/acre).

Is your point that N was not economical most years or that you were understocked or that you had great legume stands?

My point is our yields with legume mixtures were as high or greater than neighbors using N fertilizer so we had no motivation to use N.

In our county in MO the average carrying capacity was 4-5 acres/pair for year-around, so we were over twice the stocking rate with no N-fert.

In our valley in ID with a 95-105 day growing season (6000 ft elevation & only two calendar dates (July 26-27) that it hasn't frozen at some point in the past), most ranchers consider 3T hay yield to be doing well with a 2-cut hay system. So we're doing 150% of what most neighbors are doing with no N fertilizer and some P added the last two seasons based on soil tests. We will not fertilize anything this year. That is grazing yield under center pivots, not hay yield as we don't make hay on this part of the ranch. We calculate grazing yield as 1 AUD = 26 lb dry wt forage. If we convert the grazing yield to hay equivalent, then our pasture yield would be equivalent to about 6 tons hay/acre.

 

[JRGidaho`]

fargus,

I'm still missing something. What was wrong with your calculation? An acre 6" slice does weigh 2,000,000 lb and one percent of that would be 20,000 lb. So a 1% increase in OM would be 20,000 lb more OM added to the soil.

I know 20,000 lb crop residue would not translate to 20,000 lb OM. Is that where you're saying you were off?

What gives?

jr

 

[JRGidaho`]

I think I get it. So I let the forage get taller, flatten it with mob density, take a shallow 3" deep sample including as much litter as possible, and then brag about my OM. ;-)

On a more serious note, one of the reasons given for the typical forage production decline a couple years after tillage - - is that the OM exposed by mechanical tillage has been consumed.

I think 9 times out of 10 it is simply a matter of grazing management that doesn't allow the newly seeded pasture crop to thrive. i.e. not managing for optimal leaf area for solar energy capture. Almost every pasture I have ever seeded has only gotten better over time.

 

[novatech]

This may help in your calculations. A cow produces 1.6 cubic feet of manure per day. As per this link; http://extension.missouri.edu/publicati ... px?P=EQ351
Add for the root system and non eaten forage. Legumes do not add much organic matter as they decompose rapidly.
The root system is approximately the same size as the vegatation depending on the grass.

 

[fargus]

fargus,

I'm still missing something. What was wrong with your calculation? An acre 6" slice does weigh 2,000,000 lb and one percent of that would be 20,000 lb. So a 1% increase in OM would be 20,000 lb more OM added to the soil.

I know 20,000 lb crop residue would not translate to 20,000 lb OM. Is that where you're saying you were off?

What gives?

jr

Nothing really wrong with it. The part that doesn't translate is how much is rapidly decomposed by soil microbes and released as CO2 as a part of respiration. If you took a soil test a week after plowing that crop down you might be close to a 1% bump. But the C:N ratio of the grain portion would be such that it would decompose (or germinate) rapidly, and a significant portion of that would be lost. All I was saying was my numbers were rough ones that I pulled off the top of my head, I didn't do any fancy calculating.

I guess the other comment is that the newly incorporated (hypothetical) wheat crop isn't "active" OM yet. It is doing a lot for microbial activity, but isn't OM as we think of it providing more CEC. It does offer some more water-holding capacity, but not as much (as a percentage of its own mass) as the stable mid-term and long-term soil carbon sinks. I don't have any citations to support what I said either, just basic concepts from my Soil Management courses at university.