Abstract: Summary Twenty surface soils from four main Soil Groups in Malawi and their sub‐soils were divided into three groups based on cation exchange capacity (group I, CEC < 50; group II, 50–100; and group III > 100μeq g –1 ). In each soil group the maximum amounts of K removed by successive extraction with 0.005 M CaCl 2 solution were well related to the potassium potential pK–0.5p(Ca + Mg), exchangeable K, ‘step K’, and the quotient ‘step K’/CR.K, where CR.K is ‘constant‐rate’potassium. In Group III soils only, ‘step K’/CR.K values were significantly correlated with pH, clay, and CEC, and this suggested that the soils were relatively rich in K + specific binding sites. In 27 soils from an NPK factorial experiment on tea, the rate of depletion of extractable K reserve increased with ammonium sulphate treatment, whereas K fertilizers tended to off‐set significantly ( P = 0.001) the depletion of K reserve. The values for the change in free energy ΔG = RT In a K / (a (Ca+Mg) ) ½ , ranged from –12 to –16 kJ mol –1 , and field observations showed that tea plants growing on soils having ΔG values less than –15 kJ mol –1 responded to K fertilizers. The investigation has indicated that heavily cropped soils are likely to show crop responses if the intensive cropping system does not include supplementation of K.
Publication Year: 1980
Publication Date: 1980-09-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 4
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