Determination of Available Phosphorus in Soil by Ultraviolet-Visible Spectrophotometry and Its Application of Fertilization in Epimedium Experimental Field

A method for determination of available phosphorus in soil by ultraviolet-visible spectrophotometry was proposed. 2.5 g of soil sample that had been air dried, grounded and sieved through a 1 mm-sieve was taken into a 100 mL-centrifuge tube with a stopper . 50.0 mL of sodium bicarbonate extractant was added, and the mixture was sonicated for 10 min at (25±1) ℃ and centrifuged at a rotational speed of 8 000 r·min⁻¹ for 5 min at (25±1) ℃. 10 mL of the supernatant was taken and made its volume up to 50 mL with water,and 5.0 mL of molybdenum antimony anti-chromogenic agent was added. It was placed in a constant temperature oscillator and shaked for 1 min. 10 mL of water was added and the mixture was shaked for 1 min. After settling at 25 ℃ for 30 min, colorimetric measurement was performed at a wavelength of 880 nm in 1 cm diameter colorimetric dish with the zero concentration point of the phosphorus standard solution series as the reference. As shown by the results, linear relationship between absorbance and mass concentration of phosphorus was found within 1.0 mg·L⁻¹, with detection limit (2.528s) of 0.107 mg·kg⁻¹. This method was used to analyze the standard substances of effective soil component analysis at 4 concentration levels, and the determined values were all within the uncertainty range of the certified values, with RSDs (n=6) of the determined values less than 5.0%. This method was also used to analyze soil samples before and after fertilization in epimedium experimental field, and the determined results were basically consistent with those by NY/T 1121.7—2014.