A laboratory incubation study was used to compare potassium (K) adsorption in two New Zealand soil types (Tokomaru silt loam and Egmont brown loam) of contrasting mineralogy when K was applied as either dairy cow urine or potassium chloride (KCI). Following incubation with urine, soil pH increased within 24 h on both soils. For the Egmont soil, the increase in soil pH increased the pH -dependentnegati ve surface charge which resulted in greater K adsorption from urine than from KCl. In contrast, the Tokomaru soil with smaller amounts of pH -dependent charge, displayed no difference in the degree of K adsorption between the two K sources. These results suggest that field prediction of K leaching losses in the Tokomaru soil will not be dependent on the form ofK used, but for the Egmont soil there may be a greater proportion of K lost from potassium chloride compared with urine.
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