...........A few years back I saw an interesting publication from a smaller technical unversity in Mexico, on the internet only as far as I know, and the link is now dead, of a licenc. or grad student who had found that tarwi was highly effective in maintaining the availability of added P fertilizer, compared to plain bulk soil where P fertilizer was fixed. He or she called it an "efecto coadyuvante", a pesticide metaphor...

That is part of the story that I'm researching in Potosi, is Tarwi and other legume's interesting relationship with soil P.

Saludos por alla --
Steve

Steven Vanek
Graduate Student
Soil and Crop Science, Cornell University
Casilla 3183, Cochabamba BOLIVIA

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From: Rolando Bunch
To: MULCH-L@cornell.edu
Date: Thu, 27 Oct 2005
Subject: RE: Tarwi seed

Friends,

The availability of P fertilizer in the soil is greatly increased by the addition of any large amount of green organic matter to the soil. Is there any reason to think the organic matter from tarwi would do this better than that of any other green organic matter?

Sincerely,
Roland Bunch

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From: YankeePerm@aol.com
Date: Fri, 28 Oct 2005
Subject: Re: was Tarwi seed Phosphorous accumulation
To: MULCH-L@cornell.edu (MULCH-L)

Many legumes are phosphorous accumulators. I do not know if this is the case with tarwi.

DH

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To: MULCH-L@cornell.edu (MULCH-L)
Date: Sat, 29 Oct 2005
From: Dennis Argall

Subject: Re: Tarwi seed

Lupins have proteoid roots, which accumulate phosphorus.

http://www.tau.ac.il/~ecology/virtau/3-philip_nemoy/cluster_roots.htm

A number of Australian native plants also have this adaptation to ancient soils with very low phosphorus levels. Many of these keel over when farming adds superphosphate.

In the eucalypts there is another adaptation... I have been told in the past that eucalyptus oil is a by-product of a complexity in ATP synthesis in phosphorus deficient soils but have no source for that now. Hence the super-weed behaviour of eucalypts in some exotic poor soils situations.. poor locally maybe but rich compared with natural home soil circumstances of many eucalypts.

In our small organic garden environment, Hakea self-seed and we allow them some growth among food plants. Acacia, of course, self-seed, as do casuarina, both pioneer species on damaged soils; both nitrogen fixers, but I understand they raise rather than lower pH, unlike peas and beans (can't speak for lupins). We use fast-growing self-seeded acacia for multiple functions - deep soil opening, deep soil organic content increase, nitrogen fixation, frequent pruning for mulch, shade for things like coffee, climbing frame for beans, etc. Conventional farmers having bulldozed acacia and applied superphosphate marvel at effect, but effect over time is probably mainly three year nitrogen effect from acacias. We have trouble getting lupins to grow strongly, doubtless and inoculant absence with sequela of a weak plant-hungry slug synergy.

This is no case for use of hakea, acacia, casuarina anywhere away from home; observation of local thrivers seems best to me... I like to compare soil keeping with bee-keeping; good production depends on generous support and skilful theft in natural circumstances.

Should we seek to carry things like lupin and their bacterial associates everywhere, or work on natural local soil communities?

Dennis Argall
Austrailia
www.aplaceof.info

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From: Steven Vanek
To: MULCH-L@cornell.edu
Subject: P and organic matter/plant species

Well, it seems like an interesting discussion developing -- some thoughts --

- To me this partly boils down to the quality vs quantity "debate" (discussion, really) on soil OM or green manures -- ie, is it mostly the quantity of organic substrate you add to the soil (or that you add in fertilizer) and the N, P, K, and micronutrients that come along with it that are relatively easily cycled through soil microbes and liberated to plant roots at some point along the way...

--AND/OR (prob. more AND than OR) are there particular species with qualities of doing a really good job of accumulating P (or N or K), from either native, tough to get at sources, or applied organic/inorganic NPK. People seem excited about Tithonia/P in this regard, no?

-- AND/OR are the rhizosphere effects of particular species of legumes, grasses etc. effective in making nutrients more available, independent of the nutrients accumulated in the roots or aboveground biomass -- for example white lupine with proteoid roots, that would leave zones of soil with P that has been solubilized by chelation activity of organic acids, and has even been shown to be able to "feed" P to wheat plants in association where the roots overlap.

-- There are a lot of fancy mechanisms that have been suggested about plants/P (proteoid roots, soil acidification by N-fixing legumes, mycorrhizae), However Roland's suggestion that presence or "just plain quantity" of organic matter (and P content, it would seem) is one of the largest factors, makes a lot of sense to me and is supported by lots of experiences in lots of places. P associated with organic matter has a "slow, but not too slow", pattern of release and OM in general is likely able to block the fixing ability of aluminum and iron oxides in soil.

-- White, blue, and several other lupines I think have proteoid roots, but from what I've read so far, Tarwi is not thought to have this adaptation (Sooner rather than later I'll go looking for some on tarwi). To me that doesn't make me positive that something interesting isn't going on with Tarwi and P. It seems to be able to accumulate large amounts of P (just based on typical harvests and grain P content) in soil situations that are far from optimal. Soils in the Bolivian highlands are of course a lot younger than some in Australia, but can also be quite depleted.

- I'd love to hear more about the P/eucalyptus story-- another plant besides Tarwi that surprises one with an ability to survive in relatively low P soils. Mycorrhizae might be part of the story there?

- An interesting and lengthy review of what we know and don't know about plants relation to soil P is

Hinsinger, Philippe. Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review. Plant and Soil 237: 173­195, 2001.

Best to all,
Steve