POTASSIUM AVAILABILITY AND SOIL EXTRACTION TESTS IN AGRICULTURAL SOILS WITH LOW EXCHANGEABLE POTASSIUM CONTENT

Potassium availability and soil extraction tests in agricultural soils with low exchangeable potassium content

Potassium availability and soil extraction tests in agricultural soils with low exchangeable potassium content

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Low application of fertilizer potassium (K) in intensive agriculture leads to a gradual decrease and, afterwards, to a steady state of soil K determined by michael harris sunglasses tests which are based on soil exchangeable K (Kexch) extraction.In this situation, non-exchangeable K (Knon-exch) is being released and therefore real plant availability does not necessarily correspond to soil test K.This incoherency was investigated in 14 agricultural soils with low K as determined by the Mehlich 3 method.Plant-available K released by exhaustive cropping of perennial ryegrass and K determined by the Neubauer seedling test were compared with 8 soil K extraction methods, with the total K content and with the relative content of soil K-bearing minerals.K determined by the ryegrass test (314 mg/kg on average) was more than 3-times higher than K based on Kexch extraction methods, but was from us polo assn mens sweaters 2 to 3 times lower than K determined by Knon-exch extracting methods.

The relative content of mixed-layer phyllosilicates was significantly related to K extracted by soil tests.The relative content of orthoclase correlated only with total K and mica-group minerals with none of the extractions.The best prediction of plant-available K in investigated soils was obtained with sodium tetraphenylboron and StepK methods.

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