Wednesday, December 12, 2007

Why we love the N-fixers anyway

So in most urban lot forest gardens, you probably don't need nitrogen-fixing plants for their nitrogren input if you're recycling your urine. I'll throw out some reasons to keep them around anyway:

  • Long-term stability. If something happens to change your urine-recycling contributions to the forest garden, nitrogen fixers will still keep the nitrogen flowing if you've designed them well. Crack-down by the neighborhood association on renegade pee-ers-in-the-night, exodus of your housemates on whom you depended for their piss, or selling your property to mainstream squeamish folks could all leave your forest garden without the nitrogen inputs it needs for optimal performance.
  • Ongoing slow release of non-messy fertilizer. For patches where you're growing salad greens you want to harvest frequently, n-fixers provide a much cleaner nitrogen source than splashing your piss around.
  • Frees up your nitrogen for application elsewhere. Knowing that you have ample nitrogen available at home, you can gleefully fertilize wild patches of vegetation, injecting helpful nutrients to partially compensate for the abuses they suffer from civilization. I find it a lot easier to go pee in the woods and grow a Goumi at home than to plant and tend a goumi in the woods and pee at home.
  • Other uses. Many nitrogen fixers have other uses which warrant their inclusion in your food forest regardless of their nitrogen contributions. Off the top of my head, I can think of nitrogen-fixers which also provide or act as ground covers, fast growing cover crops, tea, human food, wildlife food, chicken forage, bee nectaries, foot-tolerant steppables, and dynamic accumulation of phosphorous and other nutrients.
  • Learning about particular plants through direct experience now. When we move to a rural area and start growing quarter acre food forests per person, we won't be able to fertilize the whole area from which our food comes. I feel glad that we're currently growing Elaeagnus, pea shrubs, black locusts, and various herbaceous nitrogen fixers which I expect to use in our larger systems in the future. If you ever design or give input for project for squeamish neighbors or friends, or for public demonstration gardens where the public "ick" factor precludes urinal input, then having experience with n-fixers will allow you to do a better job of integrating them into a system which actually needs them.


Bpaul said...

All very true, and good points.

Jim said...

I enjoyed your pages on urine. I have been using it to fertilize our new food forest for several months now. Do you have anything on how much to dilute it for safe use. I burnt a meyer lemon that was blooming beautifully. It is sadly in a pot for now. That may have contributed to its burning. It lost all of its flowers (bummer).
Also do you know of a very low i.e. 3-4 inch high nitrogen fixer that I might put in the pot with the lemon?

FarmerScrub said...

Hi Jim,

I don't have any specific, hard guidelines on urine dilution, though I have seen many people offer dilution requirements, such as 1:10.

I usually pee directly on plants and haven't noticed problems--I do try to spread my peeing spots around the garden a lot so no one area or plant gets too heavy a dose. I do drink a lot of water myself so usually my pee is clear, already reasonably well diluted.

When I dump our pee bucket from inside, sometimes I dilute it as little as 1:1, but more often I try for 1:3 or 1:4.

I really like Lotus corniculatus "Plena" or "Plenum", the prostrate bird's foot trefoil, as a 1-2" creeping N-fixing groundcover. As far as I know, it does not come true from seed, so you have to get a vegetative clone.

The other low-growing N-fixer I know of, Trifolium repens, white dutch clover, grows about 4-10" tall according to Edible Forest Gardens, so may get too tall for what you want.

Hope that helps!

Norris said...

See also this comment on benefits of using n-fixers even if you have enough nitrogen...

talus wood said...

Are there any studies to show how much nitrogen fixers actually supply? Theres been some talk that this is a bit like the chicken greenhouse saga. I.e everyone recommends it, does it really work (very well)?

Norris said...

Good question, talus wood - enough unsubtantiated claims are thrown around in permaculture circles and literature that I think it wise to perform due diligence.

In this case, I think there's ample research to back up the claims, from pre-industrial-ag traditional wisdom, to modern scientific measurements.

I've been keeping track of n-fixing rates as I come across them, and have this list, in pounds per acre per year:

Casuarina equisetifolia 36-90
Gliricidia sepium 12
Leucaena leucocephala up to 244
Jicama 136-170
Erythrina poeppigiana 54
Inga jinicuil 31-36 or 44
Hippophae sp 53-158