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Old August 21st, 2006, 03:57 PM
hortus hortus is offline
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excess potassium--mitigation

A recent lab test shows that the major nutrients in my vegetable garden soil are all very high, except for the nitrogen. The potassium was measured at 814 ppm, whereas the recommended level is apparently 50-250 ppm. The lab said that the high potassium level was interfering the plants' ability to utilize other nutrients. A 50/50 mix of manure/compost was applied to the vegetable bed last December. No weeds grew in it in the spring, which was somewhat odd. After rototilling in May, I planted vegetables as usual but most seedlings turned red and died soon after germinating. Tomatoe and broccoli transplants grew very little after being planted. The dismal plant growth prompted the lab test. Does anyone have thoughts on how to correct the potassium problem?
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Old August 21st, 2006, 07:12 PM
Ralph Walton Ralph Walton is offline
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Re: excess potassium--mitigation

Excess potassium (K) is also a farmer's problem and is associated with manure applications. Most of the potassium in the feed (hay & silage) is returned to the fields in the manure (particularly urine or mixed manure). Excess K can also interfere with the absorbsion of other nutrients and micro-nutrients even though they may be present in the soil. The resulting problems seem to be one of balance (particularly Ca:K) rather than simply excess, and is accordingly treated by adding the deficient components. Since there is no practical way of adding elementals (single elements) to the soil, various compounds are used such as calcined magnesia (MgO), gypsum (CaSO42H2O), superphosphate (Ca(H2PO4)2 + 2CaSO4) and no doubt many others. MgO is typically used in pasture treatments as one of the effects of excess K is a reduction of Mg uptake leading to grass tetany in livestock, and is probably not relavent to your situation. As you can see from the formulas, gypsum will also add sulphur and superphosphate will add both sulphur and phosphorus in addition to the desired calcium. Gypsum is also a useful structural ammendment for some clay soils.

You will need some good specific advice; I suggest a commercial nursery supplier like http://www.growercentral.com/
who have an outlet in your area.

Ralph
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Old August 27th, 2006, 09:26 AM
hortus hortus is offline
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Re: excess potassium--mitigation

Thank you for your comments. I'm going to visit the local Evergro in the next day or so. One concern I've had is whether the potassium and other salts may be so high that reverse osmosis in the roots might be occurring. If that was the case, presumably that problem would continue even if the major nutrients were brought into balance with each other by increasing the nutrients that are currently low in relation to the potassium, etc.
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