Question about nitrogen fixing trees

Another "hhhmmm" moment for me. I was doing my yearly planting of trees. I was on pecan trees. I spotted a location and went over to dig a hole. Very close by is a mesquite, a nitrogen fixer!

Now im confused. Do i plant there because its feeding nitrogen in the soil,  or do i NOT plant there because if the mesquite is there the soil must be deficient in nitrogen.

Its kind of funny if you think about it.

I wondered what the answer would be if put in a poll form. 50/50? Maybe someone smarter than me could insert a poll into this thread and see.

Good question Wayne,

The genus Prosopis, lately also called Fabaceae, are legumes that fix nitrogen to the soil, not into nodules which are part of the root system.
This means that the nitrogen the species puts into the soil can be used by other plants immediately. Some of the species of Prosopis have edible seeds too.

I would go ahead and plant that pecan tree or perhaps even two spaced one to either side of the mesquite, just don't put it (the mesquite) in the position of ending up shaded out, these trees love full sun.

Redhawk

N-fixing trees are primary colonsiers, so your mesquite might be there simply because there was some localised soil disturbance that allowed it to establish. I like to think of the ecology as a living 'thinking' entity, so in your case the tree is trying to establish the first step on the way to forest. I don't think you can draw conclusions about the N status of the soil based on the presence of legumes, this is too reductionist.

I've planted over 50,000 N-fixing tree here, mainly Alnus acuminata and Acacia elata, dealbata, melanoxylon and silvestris. It is surprising how the site does not necessarily predict results; these trees grow best on high fertility moist sites, and struggle on the hard dry sites I want them to thrive on. Soil interactions are far more complex that some of the simplistic N-fixing tree enthusiasts suggest.

I would suggest considering your pecan/mesquite planting site in terms of competition and alleopathy rather than Nitogen status.

Ben, out of curiosity, have you planted much tagasaste? It seems to do best on drier sites (I always see heaps of it along the roadsides when we head to the East Coast beaches). We've got lots of it growing in our shelterbelts and I raise seedlings for planting out in other places, but the establishment is almost always poor and even if the tree lives and grows for a few years they typically give up. Meanwhile, the ones in the shelterbelts do just fine and get to a decent size. I'd like to intersperse them with the fruit and nut trees but am not having much luck. Things I've tried include lots of wood chip mulch, putting in a spadeful of soil from under a larger tagasaste to jumpstart the mycorrhiziae, and keeping the pasture at bay when they're little. Meanwhile, A. melanoxylon grows like a weed for me and puts up shoots 10-20m away from the big trees.

Hi Phil,


I've planted isolated trees for years, but my main experience was when I planted about 15 acres of tagasaste for stock feed about 25 years ago. I'm not a fan, even in my 1000-1200mm rainfall area tagasaste seems pretty alleopathic, and not much grows under it. It's good if it's kept constantly grazed, but once it gets a chance to grow it seems destined to die. The animals eat all the seedlings which is good. By contrast A. melanoxylon seems to allow understorey growth, produces a great microclimate and eventually produces a top quality cabinet timber. I look at habitat and it makes sense; tagasaste is native to an arid island where everything has to fight to survive, the plant is designed to kill competition.... which it does very satisfactorily. A. melanoxylon at it's best occurs in rainforest with a high biodivesity and mixed species under its crown. What is best for permaculture, high competition species or highly tolerant trees? The answer depends on your design goals, but for me I go with rainforest trees.

I've planted over 200,000 eucalyptus trees too, same rule applies here but more so!

Just because a mesquite is growing there does not mean that the soil is deficient in nitrogen.  It simply means that a seed fell into a good location and it sprouted there.  If, perchance, the soil is poor, the mesquite will help with that.  But if it's good soil, the mesquite will thrive all the more.

Maybe mesquite would not germinate / succeed within it's first year of growth if the soil was already nitrogenated?  Do I make sense?  Wondering.

Looks like its unanimous. I did plant the pecan but cant plant on both sides.  Im planting on the edge of an existing treeline.

While peeps around here hate mesquite, i want to try the seed pods. I hear they are 30% sugar and was a candy for old settlers children.

Wayne, why is mesquite hated? Which species do you have? Do they grow straight? I've often thought about growing some, which species is best, and are any thornless?

wayne fajkus wrote:Looks like its unanimous. I did plant the pecan but cant plant on both sides.  Im planting on the edge of an existing treeline.

While peeps around here hate mesquite, i want to try the seed pods. I hear they are 30% sugar and was a candy for old settlers children.

 Dude what, candy what and also awesome smoking wood chips, heck ya

Ben Waimata wrote:Wayne, why is mesquite hated? Which species do you have? Do they grow straight? I've often thought about growing some, which species is best, and are any thornless?

They are thorned. Very big thorns.  The reason they are hated. I have no idea about varieties/species.

Ryan A Miller wrote:

wayne fajkus wrote:Looks like its unanimous. I did plant the pecan but cant plant on both sides.  Im planting on the edge of an existing treeline.

While peeps around here hate mesquite, i want to try the seed pods. I hear they are 30% sugar and was a candy for old settlers children.

 Dude what, candy what and also awesome smoking wood chips, heck ya

I had read that back in the old pioneer days  children sucked on the seed pods cause they had 30% sugar. I think Wikipedia was my source.

The Texas variety is probably honey mesquite (Prosopis juliflora). Where I grew up we had mostly velvet mesquite (P. velutina) and I ate mesquite beans by the handful as a kid (and grown up). We used to go around to people's houses and offer to rake them up for free, bagged them and brought them home for the goats. Excellent source of sugars with a high concentration of polysaccharides. Our mesquites weren't too thorny and the filtered shade plus N-rich leaf litter meant that you found lots of life under the canopy. Wonderful trees. Ranchers hated them...ironic because cattle love the beans and helped spread the trees from the bottom lands onto the entire range.

I have thousands of mesquite on my ten acres in South Texas. I have heard from the old timers that mesquite is hated also, But I actually chose this land because of the savannah quality, and the possibility of nitrogen production going on down there.  

This is a guess informed by Mark Shepard of Restoration Agriculture, who three day workshop I took two years ago. His brand of agriculture is really revolutionary (for example, his opinion of honey bees is, TAKE 'EM). He plants perennials of commercial value, particularly the chestnut, which produces a starch and which is much in demand in the world market, with enough space between them to allow light to the under storage, where annuals and grazing species can be planted, for faster income. He is one of the founding members of organic valley.

The species of plants that he chooses are all based on the kind of environment the farmer finds him or herself in. He thinks that people in Texas who are planting varieties of fruit trees for example from biomes vastly different from the one you are in are stupid--that if you live in a land of cactus, rather than try to force an apple orchard uphill you should try to consider yourself a cactus farmer, and find markets and outlets for those products your land raises naturally-- even if it means the sales arm reaches out of your land.

Using species interspersed with trees come from the observation that the African Savanna is the most productive biome, in pounds of mass, in the world.

If any species requires daily handling from you, you've got the wrong thing. He is well known for the phrase "STUN" agriculture: shear, total, utter neglect. If it requires your daily investment, you're working too hard, forcing something that's not supposed to be there.

This is the advice I took, and I'm trying to build a sustainable agricultural program around the tree cover, (almost all mesquite), that I have. For sure, the grass and ground cover grow far better in these interspersed trees in the middle of summer than anything growing in broad daylight, which is fried to a crisp by June.