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South Bloomfield, Ohio

I know that AG's are potassium-loving plants. My questions are as follows:

1. Does potassium need to be in balance with other elements in order to be readily taken up by the plants? If so, what are they and what ratios are involved?

2. Is potassium tied up by other elements? My spring soil test came back with potassium at 291 ppm which was very high, but optimum for AG's. This patch was not grown on last year, which leads me to believe that the potassium was not used to its full potential the year before last.

6/28/2008 11:34:55 AM

Ohio

The only thing I can think of Joe is proper PH levels for good up take in Potassium, and I know you already know that one, other then that Im not sure. But just curious, what was your potassium levels the year before last?

6/29/2008 5:16:38 AM

Kevinstinindians@yahoo.com

Factors Affecting K Availability
Soil CEC: Plant-available soil K is in the ionic (electrically charged) form. This charge is positive, making K a cation, represented as K+. Cations are attracted to, and held by negatively charged colloids (primarily clay and organic matter) that make up the cation exchange capacity (CEC) of the soil. The larger the CEC, the more K that can be held by the soil and the higher the soil test needed to adequately feed plants.

Soil test K:Higher soil test K increases the available K, by increasing the amount and balance of K relative to other cations.

Cation Balance: Where there is a significant imbalance between available K and the other major cations (Primarily Calcium, Magnesium, and sometimes Hydrogen, Aluminum, or Sodium), it may affect the availability of K to the crop.

Soil Moisture: K is transported within the soil and is absorbed by plant roots in the soil water. Therefore a water deficiency results in less K absorption.

Soil pH: As the soil pH is reduced (increasing soil acidity) the availability of K is often reduced.

Soil Temperature: Cold soils often reduce the availability of K.

Soil compaction: Compacted soils often reduce the availability of K.

Soil Drainage/Aeration: As soil drainage is improved, K uptake typically improves.

Soil Salinity: Saline soils often have excess sodium (Na). One of the negative effects of excess Na is that it reduces the availability of K.

6/30/2008 9:18:08 PM

Kevinstinindians@yahoo.com

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K/Mg ratio: Each of K or Mg can reduce the uptake of the other when the "normal" soil balance does not exist. Typically, we find high K levels inhibiting the uptake of Mg. However, some Midwest soils have enough Mg to reduce K availability, especially to high-demand crops.

Other Cation ratios: There are occasions when K uptake might be restricted due to an imbalance with other cation elements in the soil. For example, in many high pH soils there is an excess of Ca. Competition from this Ca could reduce uptake of K. Strongly acid soils will often have an excess of hydrogen (H), aluminum (Al), iron (Fe), and possibly other cation elements. These excess elements can compete with K for entry into the plant, and/or set up soil conditions that are unfavorable to efficient K utilization.

Soil pH: This subject is intertwined with both of the previous points. While we don't think of K as leachable, in acid soils with low CEC's, we find that K can be leached somewhat. Where initial soil tests or fertilizer programs are not sufficient to offset this loss mechanism, we can see lower yields and crop quality.

Balances and Ratios

It is generally accepted that there are some preferred general relationships and balances between soil nutrients. There is also a significant amount of work indicating that excesses and shortages of some nutrients will affect the uptake of other nutrients. However, no reliable research has indicated that there is any particular soil ratio of K, Ca, and Mg that is uniquely superior to another ratio.

High soil Mg can reduce K uptake, but it seems to occur only when the soil Mg saturation is in the range of 25% to 30%, or higher. We have not identified a particular K:Mg ratio that is significant in causing Mg to reduce K uptake.

6/30/2008 9:21:27 PM

South Bloomfield, Ohio

Farmer,

Your information is very pithy and thought-provoking. You went way out of your way to answer my questions.

I think that, once some grower takes the time correlate the data you provided from the beginning of the growing season to the very end, more insight will be obtained. Generally speaking, tracking the amount of available K at the beginning of the season until the end.

Your response is very much appreciated. Where did you obtain your information?

6/30/2008 11:17:09 PM