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Soil, Compost & Mulch

too much phosphorus

14 years ago

I recently had the soil tested in my raised vegetable garden box. The test results state that there is an extremely high level of phosphorus in the box. Per the attached guidance from the extension office, excess phosphorus can lead to an iron deficiency. Could this be why my tomato plants are somewhat stunted looking and the leaves are yellow-ish? And why my zucchini plants are barely a foot in diameter while my neighbor's (with whom I shared a six pack of plants) has zucchini that's about three feet wide? Other than the excess phosphorus, I hope the soil is basically fine? 6.9 pH and medium - high levels of potassium, magnesium and calcium. Any thoughts?

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Comments (9)

Kimmsr
14 years ago
Excess soil Phosphorus levels can keep your plants from uptaking Zinc, Iron, and Cobalt, all essential micronutrients and that could be why your tomatoes are stunted and chlorotic.
What is the level of organic matter in your soil?
Michael
14 years ago
Definitely can be the problem, hinders Mn and Zn uptake also.
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Ah, I missed the point. A clarification: 'stay' on top of the soil, in that (using my example) those nutrients are not 'leaving on the truck' like they would with a cash crop. No, they'll stay right there, on the lawn. While staying right there, they're susceptible to washing away, or leaching, or just staying there. But the point is, what you don't need at that point is to be adding more. While it's not true that every speck of excess (more than the lawn crop will use) phosphorus will wash away (or leach), it is true that the creation of the excess is what allows, even causes, the problem. So we don't need to be adding more phosphorus. There's enough there, right now, on that lawn.
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There have been a number of lengthy discussions about such amendments at the soil forum recently - look through the last few pages.
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The raised beds were planted last summer with perennials, the reason I had the soil tested was because the plants did not grow much and some leaves turned brown. The extension agent said to just let things be for a couple years, the plants will survive but may not grow much. I do plan to add a few containers to the bed where there are some bare spots to fill in until I can plant in the ground again. I agree it is always a good idea to have the soil tested since often the company that sells the topsoil isn't aware of any specifics that may result from it's place of origin. I am in a wheelchair and raised beds definitely make gardening easier so it's worth the extra effort.
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Blueberries need a soil pH of 4.0 to 5.5. Our tap water has a pH of 7.5 so watering with this water will drive the soil pH up quickly. The only way to maintain the soil pH is to water with low pH water. The pH of rain water is around 5.0 to 5.5. Using rain water is probably all you need for blueberries to be healthy. You could add a little acid to the 5 gallon bucket if you feel the soil pH needs to be lower. I use 85% phosphoric acid so very little is needed, for me it is 3ml in 5 gallons of tap water every two weeks. I chose phosphoric acid because plants need phosphorus. You could use other acids too like sulfuric or citric. The manufacture of a sanitizer I use at work stated that their product is not only environmentally friendly it is actually good for plants as it lowers the PH of the soil. The guys growing grapes down the road told me they inject acid into their watering systems to control pH. That is how I got the idea to use acid in the water. It has worked very well for my blueberries so far. My question restated is - is a build up of phosphorus something to be concerned about? If it is then using a fertilizer that does not contain any phosphorus would be a good idea. Maybe changing the type of acid every once in a while too.
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gargwarb
14 years ago
I don't believe I've ever seen a cobalt deficiency. Not saying it doesn't happen but what would it look like?
Kimmsr
14 years ago
Cobalt is a micro nutrient that can contribute to chlorosis, yellowing of the plant leaves.
gargwarb
14 years ago
It's my understanding that cobalt is a non-essential element and that plants can get along just fine without it, but may derive some small benefit if it's there. I can't seem to find a single documented case of cobalt deficiency causing chlorosis in plants.
This best I could come up with was this:
"cobalt probably participates in chlorophyll b formation"

But there is nothing about cobalt being vital to the process, only that it "probably participates". (Earlier in the article it actually states that decreasing cobalt increases 'chlorophyll a' and chloroplast production). Nor are there any documented cases of a cobalt deficiency or a statement of what symptoms might be expected if cobalt uptake were low.

Can you help me out and point me towards any documentation supporting the claim that cobalt deficiency leads to chlorosis, or any other symptom, in plants?

By the way, if you read through that article there is all kinds of fun stuff. Like this: "Apical application of COC12 (50-100 ~tg/plant) to female plants of Cannabis sativa
caused drying of the shoot tip and formation of axillary branches which bore male,reduced male, and intersexual flowers along with female flowers."

In other words, you better not spill your cobalt on your pot plant unless you want to give it a sex change.

See kids? Who says science ain't fun?
Michael
14 years ago
I heard that germanium and tellurium do the same thing.
gargwarb
14 years ago
kimmsr, can you help me out?
Kimmsr
14 years ago
since plants only need miniscule amounts of Cobalt there has been very little research into what it does for plants, except for some notes that it can contribute to chlorosis and might be necessary for proper development of chlorofil.
Soils with adequate levels of organic matter will seldom have Cobalt deficiencies.
ericwi
14 years ago
My understanding is that cobalt is known to be part of the structure of vitamin B12. B12 is produced by bacteria, not by plants and animals. One can imagine how B12 gets into fish tissue, working its way up the food chain. I am not clear, however, how it gets into land animals, like cows, for instance. Either it is taken up by plants, which end up as forage for the cow, or it is produced by bacteria living in the gut, and absorbed into the bloodstream of the animal, across the intestinal wall. It seems possible that cobalt is essential to maintain a full spectrum of soil bacteria, and that this could contribute to plant health. I think there is more that we don't know about soil bacteria, than there is that we do know. As if knowledge could be counted and quantified.

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