Sodium Bicarbonat-DTPA Tefst as a Simultaneous Extractant for Micro nutrients in Soil

The methods used currently in Iran's analytical laboratories for determination of single elements in soils are found to be expensive and time consuming. This study presents a quick and inexpensive method for simultaneous extraction of soil macronutrients as well as micronutrients. The new extracting solution used in this procedure consists of NaHCO3 (at 0.5 molar concentration), and DTPA (at 0.005 molar concentration) adjusted to pH 7.6 ± 0.05, the sodium in the extracting solution acts as an extracting agent for NH4, K, Ca, and Mg, while bicarbonate ion removes phosphorus; DTPA extracts Cu, Zn, Fe, Mn as well as Ca and Mg, and water dissolves the nitrates. Extraction begins with adding 2.5 g soil sample to a 125 ml Erlenmayer flask, followed by 20 ml of the extracting solution to be shaken at 180 rounds per minute for 30 minutes. Manganese, Zinc, Iron, and Copper in the extract are determined by atomic absorption after filteration of the soil extract; Phosphorus is measured colorometrically and potassium with a flame photometer. The soil concentrations of the above-mentioned elements were also checked with the more common standard laboratory procedures namely, Phosphorus by 0.5 molar solution of sodium bicarbonate in Olsen's method (Olsen et al, 1954); Potassium with extraction by one molar ammonium acetate (Ehyaee and Behbahanizade, 1993); Iron, Manganese, Copper and Zinc by DTPA and triethanol amine (pH= 7.3±0.05) method of Lindsay and Norvell (1969). Some 800 different surface soil samples with a wide range of physicochemical properties obtained in 17 provinces (about 50 sample from each province) were used to test and check the new procedure for soil Phosphorus (P) were highly correlated with those of ammonium acetate procedure; and Iron, Copper, Zinc, and Manganese values were well correlated with those obtained with Lindsay's method. Significant (P0.01) regression equations were obtained for soil nutrient concentration obtained with the new method that were mentioned. Phosphorus concentrations obtained with the new method were similar to those obtained with Olsen's; soil Potassium values were about half as much as those obtained with ammonium acetate method; Iron 1.5 times that of Lindsay's method, Zinc and Copper about 1.33 times and Manganese some what less than those of Lindsay's procedure. The critical level estimations for Phosphorus, Potassium, Iron, Zinc, Copper, and Manganese were found to be 10, 80, 7.6, 1.2, 0.26, and 2.1 mg/kg respectively using this new extraction procedure.