Evaluation of the nutrient dynamics in calcareous soils from Pakistan by electro-ultrafiltration (EUF)

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Abstract
The nutrient fractions of soils rich in CaCO3 from Punjab (Pakistan) were determined by means of electro-ultrafiltration (EUF) as well as by conventional methods. The following results were obtained. At relatively high AL-P2O5 values, the P values obtained by the Dutch water method were comparatively low and indicated an insufficient P supply. Great differences existed between the AL-P2O5 and CAL-P2O5 values which signalled the presence of barely soluble Ca phosphates. This explained the low water soluble P values of these soils. The effectively available EUF-P values obtained at 20°C and 200 V within 30 min were considerably higher than the water soluble P values and indicated a medium to good P supply. The effectively available EUF-K amounts at 20°C were lower than the contents of exchangeable K, indicating that these soils bind K ions selectively. Depending on the degree of selectivity, the EUF-K values at 20°C can be very different at almost equal contents of exchangeable K (cf. Table 2, Nos. 1 and 7). An amount of effectively available K obtained by EUF at 20°C, e.g. 14 mg, can therefore be released from these soils at contents of exchangeable K in the range of 16–31 mg (Table 2, Nos. 1 and 6).