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

Madaras, M.; Koubova, M.

Plant Soil and Environment 61(5): 234-239

2015


ISSN/ISBN: 1214-1178
Accession: 070741587

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 tests which are based on soil exchangeable K (K-exch) 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 K-exch extraction methods, but was from 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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