تعيين عصاره گير مناسب و حد بحراني فسفر براي سورگوم (Sorghum bicolor L. Var.Speedfeed) در خاك هاي آهكي منطقه بيرجند

Determination of Suitable Extractant and Critical Level of Phosphorus for Sorghum (Sorghum bicolor L. Var. Speedfeed) in Calcareous Soils of Birjand Region, Southern Khorasan, Iran

Sorghum (Sorghum bicolor L. Var. Speedfeed) is a major forage crop in Biijand Region, and phosphorus (P) plays an important role in its nutritional value. During a field campaign, eighty soil samples from the region were collected and analyzed. Among them, 24 samples varying in physico-chemical properties and available P were selected. Five extractants were used for measuring sorghum available P as follows: 1) 0.5 M NaHC03, pH=8.5, shaken for 30 minutes (Olsenʹs method), 2) 0.5 M NaHC03, pH=8.5, shaken for 16 hours (Colwelʹs method), 3) 0.0025 M Na2-EDTA, pH=7 (EDTA method), 4) 1 M NH4HC03, 0.005 N DTPA (Soltanpour and Schwabʹs method), and 5) Water (Paauwʹs method). A greenhouse experiment using a completely randomized design was carried out with 24 soil samples, two treatments of 0 and 90 mg P/kg soil and three replicates. Results indicated that all five extractants are suitable for prediction of sorghum available phosphorus, but Olson and Paauwʹs methods are preferable. The results also show ed that the critical levels of soil phosphorus for sorghum by Olsen, Colwel, EDTA, Soltanpour and Schwab and Paauw methods are 17, 24, 14, 7 and 2.5 mg P/kg soil, respectively. Statistical analysis indicated that soil pH, clay percentage and organic carbon significantly affected sorghum available phosphorus. Keywords: Soil testing, Sorghum, Critical level, Phosphorus extractant, Soil properties, Phosphorus uptake.