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Low-phosphorus fertilisers
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Posted by trish_g SE Qld Aust (My Page) on Wed, Jan 18, 06 at 18:34
Phew! That query about rainforest fertilisers did open an interesting can of worms, so I thought I'd start a new one with a question I've wondered about.
My understanding is that special "native" (low phosphorus) fertilisers are only necessary on plants which grow "proteiod" extensions on their roots, to enable them better to use the little quantity of naturally available phosphorus in "typical" Australian soil (whatever that is). These plants include the proteaceae (with the possible exception of Persoonias?) and Casuarinas, I think. Perhaps they also include some Epacridaceae, but I know little about these. According to my thoery, all other native plants should be quite happy with the amounts of phosphorus in "normal" fertilisers???
However, I suspect that there's a complication in that a little Proteaceous plant will only grow the proteiod extensions if it finds its soil to be low in the stuff. Therefore if fed fertiliser with high phosphorus from an early age it will not grow the extensions, will tolerate that kind of fertiliser well, it will continue to need it (all its life?). On the other hand, plants which have grown up in low-phosphorus soil would have well-developed proteoid roots, and would pig out to the point of being poisoned if given normal fertiliser.
Any comments on this theory? (and please use all the science you please, as authority may not have covered the topic.) |
Follow-Up Postings:
RE: Low-phosphorus fertilisers
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Good point. I am unaware of any scientific evidence for or against your theory. However, given that WA proteaceae have developed in isolation for x million years in a low phosphorus environment, they may well by evolution have lost the ability to adapt to changes in environmental phpsphorus levels, and therefore be unable to stop growing proteoid roots and have become vulnerable to toxicity. Evolution does imply the possibility of losing abilities no longer required.
Tony |
RE: Low-phosphorus fertilisers
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| I put a post exactly on this subject of proteoid roots on the rainforest plants discussion before I read this one. You might want to check it out. I am not of the opinion that all Australian Proteaceae plants are able to make such an abrupt change in their root development if the soil happens to have high amounts of phosphorous. Trish, you may be right, but in all my time as a landscaper, I am yet to see it. Banksias are very sensitive. However as I said in my other post, some Proteaceae plants from rainforest zones may well have more tolerance, as the soils are higher in nutrients. I believe Macadamias can tolerate higher amounts of Phosphorous. If it works for some folk then thats fine but I do not see the advantage in applying fertilisers high in Phosphorous to native plants. Patons make a very good cheap bulk native fertiliser. There is a strong theory that many Proteaceae plants that originate in nutrient depleted soils, also use Proteoid roots to handle heat stress in summer. Waratahs are thought to do this. There is a theory that fertilising Waratahs in summer will hinder the development of these roots and therefore endanger the plants survival. Some folk feel the loss of newly planted Waratahs in summer may be partly due to fertilising at the wrong time. It is an interesting subject. |
RE: Low-phosphorus fertilisers
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Thanks for your comments. I suspect that individual difference between plant species even in the same genus might be high. Locally the Mountain Coolibah country (Eucalyptus orgadophila) has a reputation for having somewhat higher natural levels of phosphorus, and for being poor soil for grevilleas. To paraphrase the information from a local nurseryman who lives in Mountain coolibah country and takes a strong interest in native plants:
Out there they have great trouble keeping Grevilleas alive. The worst performers having been the Robyn Gordon / Ned Kelly type. The best has been the original "Golden Lyre". Unfortunately, he says, there have been another couple of plants since which have come out under the name "Golden Lyre", but they are not the same plant. The original, he says, has blunt-tipped grey foliage which resembles G. olivaceae, and he has one which is about 20 years old (I think). Apparently a new Grevillea called "Apricot Glow", with similar foliage, has come out since then and he speculates that it would also be good on Mountain Coolibah soil. Silky Oaks, Grevillea robusta, and the G.stenomera types with "ferny-type foliage" are also successful in that area.
It would be interesting to know what other information members of this forum have derived from their own experience in areas where grevilleas are regarded as difficult to grow. Perhaps we could learn things from them about how to fertilise the plants we have? |
RE: Low-phosphorus fertilisers
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| Trish, My experience with the red-brown soils on the Toowoomba escarpment (I assume that is the soil to which you are referring?) is also that G. "Robyn Gordon" does grow, but eventually the leaves yellow, the branches die and it becomes a scrappy looking plant that I want to remove. Also most of the Banksias are even worse in the same way. Some WA Hakea spp. cope well. The G. banksii hybrids like "Honey Gem", "Pink Surprise" etc.; and also G. robusta grow very well, no problem. I have also noted a problem with whitening of the leaves of Hymenosporum flavum - I guess it must be too much phosphorus? What do you think? Cheers,
Frank |
RE: Low-phosphorus fertilisers
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Frank,
1. No, my source for the "Mountain Coolibah soil" information is Evan Prentice of Torrington Nursery, who is very interested in local natives as well as the nursery business. I'm fairly sure the soil would be of the "chocolate soil" type - the shallow, stony blacksoil of the hillsides as opposed to the heavier alluvial blacksoil of the plains - but I might have been jumping to conclusions there. I will have to check that up!
2. We are on the "snuffy" redsoil along the range, and my Hymenosporum flavum don't seem to thrive either ... I don't know that the soil is the problem, though, as other people on the same soil seem to have lovely healthy specimens. I was putting my problem down to not enough water. I'm getting self-seeding happening, so perhaps the second generation will be healthier than the first.
I find the Banksias to be highly variable. Some of them seem to have an almost insatiable need for iron chelates when they're young, but do well when larger (provided they live that long).
Trish.
P.S Of course I'm curious to know who you are. Do you get to SGAP meetings at all? |
RE: Low-phosphorus fertilisers
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- Posted by gonow NSW AUST (My Page) on
Tue, Jan 24, 06 at 21:39
| Regards the theory proteacae grown from scratch in high P soils are alright. We grow thousands from seed but with most species even native slow release is too much. I've taken to using no fertilizer in the mix and adding just a few pellets to the surface later. Worst affected are waratahs, banksias, isopogon/petrophile. Southern and western grevilleas also vulnerable. Robusta can take heaps. |
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