A comparison of four soil test procedures for determination of available phosphorus in calcareous soils of the mediterranean region

Abstract

Four procedures (desorption by anion resin, Olsen, ammonium oxalate and calcium lactate), to determine the available P in soils, were compared in a greenhouse study. Five rates of P (0, 55, 110, 165 and 220 mg/kg) were applied to 18 calcareous soils from Syria and yield response of perennial ryegrass (Lolium multiflorum L.) to applied P was measured. Dry weight of tops correlated very well with the anion resin‐P or Olsen‐P procedures while lactate P and oxalate P results were poorly correlated. Similarly, total P uptake were significantly correlated with both anion resin P (R2=0.85) and NaHCO3‐P (R2=0.82) and less so for the oxalate P (R2=0.63) and lactate P (R2=0.32) methods. All 4 soil test procedures were effective in classifying soils into responsive and non‐responsive to P. Critical soil P levels were 18.5, 11.5, 9.5 and 7.4 mg/kg for the anion resin, Olsen, lactate and oxalate soil test procedures respectively. The Olsen method is our recommendation for calcareous soils since it is a simple, rapid, and reproducible method that is well correlated with plant response.