Bioavailability of Inorganic Phosphorus Fractions in Calcareous Soils Estimated by Neubauer Technique, Iron‐Impregnated Filter Paper, and Chemical Tests

Abstract

Plants commonly suffer from phosphorus (P) deficiency in calcareous soils. Plant responses to P application on such soils mostly show poor correlation with their soil test P values. Experiments were conducted on 24 different soil samples under laboratory and greenhouse conditions to illustrate the relationship of various inorganic P fractions in different calcareous soils with P uptake by plants, P extraction by iron‐impregnated filter paper, and P soil test values estimated by 0.5M NaHCO₃ and ammonium bicarbonate diethylene triamine penta‐acetic acid. Total P in the 24 soils ranged from 652 to 1245 mgkg⁻¹ with a mean of 922 mgkg⁻¹. A major proportion (98%) of inorganic P was in HCl‐P (Ca‐bound) form. The HCl‐P (Ca‐bound) ranged from 296 to 729 with a mean of 480 mgkg⁻¹. The iron (Fe) and aluminum (Al)‐P (NaOH‐P) ranged from 0.92 to 12 mgkg⁻¹ with a mean of 1.57 mgkg⁻¹. The Fe‐P (citrate‐dithionite bicarbonate) ranged from 0.22 to 4.40 mgkg⁻¹ with a mean of 5.99 mgkg⁻¹. Data regarding P release from the soil matrix obtained by desorption with iron‐impregnated filter paper was best described by the Elovich equation. Range of slope and intercept values were found to be 5.48 to 17.3 and 17.23 to 56.27 mgkg⁻¹, respectively. Intercept values calculated for the Elovich equation may be related to labile P initially available for plant uptake in soils. Intercept values calculated for the Elovich equation correlated (r=0.77) significantly (p<0.01) with NaHCO₃ extractable (Olsen‐P)P. Significant correlation (p<0.05) of intercept with CDB‐P (r=0.44) and of slope with HCl‐P (0.43) suggested that the initially available P, regulated through CDB‐P, is replenished by HCl‐P [calcium (Ca) bound].

Keywords:

• Barley
• calcareous soils
• P availability
• P forms
• P release