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Potassium Quantity-Intensity Relationships in Calcareous Vertisols and Inceptisols of Southwestern Spain

Departamento de Ciencias y Recursos Agrícolas, Universidad de Córdoba Apdo., 3048, 14080 Córdoba, Spain

*Corresponding author.

ABSTRACT

Quantity-intensity (Q/I) curves and derived parameters provide general information about soil K availability. This investigation was conducted to study the relationship between the K Q/I parameters and the properties of 24 calcareous Inceptisols and Vertisols of southwestern Spain. Three Q/I parameters were considered: activity ratio at equilibrium (AR_o), buffer power at equilibrium (BP_o), and buffer power in the 20 x 10^–3 to 30 x 10^–3 activity-ratio range (BP_20-30). Close linear correlations were found between buffer powers (BP_20-30 and BP_o) and cation-exchange capacity (CEC) (r² = 0.949 and 0.888, respectively), and between AR_o) and initial exchangeable K percentage (EPP_o) (r² = 0.762). A good correlation (r² = 0.873) was also found between EPP and AR for all the soils within the range of K saturation studied. Twelve of the 24 soil samples were intensively cropped (nine wheat [Triticum aestivum L.] croppings); the K balance showed that 80% of the K extracted by the crops came from the nonexchangeable K pool. The Q/I curves of the soil samples after cropping were displaced upward with respect to the original ones, and the AR_o values were, consequently, lower; the displacement of the Q/I curves was similar to the decrease in exchangeable K. Following cropping, the BP_20-30 values increased slightly. In spite of these changes, the shape of the Q/I curves remained nearly unchanged; therefore, this can be considered a characteristic of the soils studied. The good correlations between AR_o and EPP_o and between buffer powers and CEC allow prediction of the Q/I parameters of these soils.

Received for publication July 26, 1990.