A comparison of methods used for the extraction of K in soils of the Western Cape

Abstract

A number of com mon soil extractants, mainly those used for soil P, were used to extract K from a range of widely differing soils which occur in the Western Cape; the objective being to evaluate the simultaneous determination of P and K availability. Soil samples were taken mainly from the upper horizons of 110 profiles representing the dominant soil forms occurring in this region. The soils varied from highly weathered, deep, well-drained acid Oxisols (Hutton form) to younger less developed duplex Alfisols (Swartland, Glenrosa and Kroonstad forms) and deep sandy Inceptisols (Fernwood form). The soils exhibited a wide range of values of clay content, CEC, pH and exchangeable K. Seven soil P extraction methods (Bray No.1, Bray No.2, citric acid 1 %, Olsen, ISFEI (Na), Ambic and Mehlich No.3) were compared with two K e~traction methods, (0.5M NH 4 CI and M NH 4 0Ac). All the methods gave K indices which were significantly correlated with one another (r> 0.9). The extractants containing NH4 + were better correlated with one another than with the other extractants. Significant linear relationships were obtained with all the methods between extractable K and soil K-values determined using the NH 4 0Ac method over a range of values from < 10 mg kg-1 to over 300 mg kg-l. Apart from the results of the Bray NO.1 and ISFEI methods, which exhibited lower extractability, all fi2 values were greater than 0.9. It appears that any of the methods used for extracting soil P are suitable for assessing the K status of the soils of this region.'n Aantal algemene grondekstraheermiddels, hoofsaaklik die wat gebruik word vir grond P, is gebruik om K te ekstraheer van 'n reeks uiteenlopende gronde wat in die Wes-Kaap voorkom. Die doel van die studie was om die g-bruik van die metodes vir die gelyktydige bepaling van P en K te evalueer vir toeganklikheid. Grondmonsters is geneem hoofsaaklik van die bogrond horisonte van 110 profiele wat verteenwoordig is van die dominante grondvorms wat in die gebied voorkom. Die grond het gevarieer van hoogs verweerde, diep, goedgedreineerde suur Oksisols (Hutton vorm), jonger, minder-ontwikkelde dupleks Alfisols (Swartland, Glenrosa en Kroonstad grondvorms), en diep sanderige Inceptisols (Fernwood vorm). Die gronde het wyd verskil met betrekking tot klei-inhoud, KUK, pH en uitruilbare K-waardes. Sewe grond P ekstraksiemetodes (Bray No.1, Bray No. 2, sitroensuur (1 %), Olsen, ISFEI (Na), Ambic en Mehlich No.3) is met twee K ekstraksiemetodes (0.5 M NH 4 CI en M NH 4 0Ac) vergelyk. AI die metodes het K indekse gelewer wat betekenisvol met mekaar gekorrelleer is (r > 0.9). Die ekstraheermiddels wat NH4+ bevat, het beter met mekaar gekorreleer teenoor die ander metodes. Betekenisvolle liniere vergelykings is gekry met al die metodes tussen ekstraheerbare K teenoor die NH 4 0Ao-metode vir grond K-waardes van minder as 10 mg kg-1 tot oor 300 mg kg-l. Behalwe vir die Bray No.1 en ISFEImetodes wat 'n laer K ekstraksie getoon het, is aile fi2 waardes hoer as 0.9. Dit kom voor asof enige een van die metodes wat...

Short-term effects of sunn hemp intercropping management in a maize-based system on the soil fertility of a Plinthic Cambisol in Free State, South Africa

“…The soil samples were analysed following standard methods, i.e., soil pH was measured with a pH meter in a 1:2.5 (v/v) soil:water suspension as outlined in Agri Laboratory Association of Southern Africa (AgriLASA 2004). Exchangeable cations (K, Ca, Mg and Na), micronutrients (Cu, Mn, Zn, and Fe), and plant available phosphorus (P) in soil samples were extracted using a modi ed Ambic 2 procedure (Thompson 1995) and determined with an Inductively Coupled Plasma Emission Spectrograph (ICP-OES) (Varian 710-ES). Total nitrogen (N) was determined in the air-dried soil samples by dry combustion using the LECO (Truspec-CNS analyser) (LECO 2003).…”