Extractability of nutrients using Mehlich 3 and ammonium bicarbonate-DTPA methods for selected grassland soils of China

This study aimed to obtain a simple and efficient soil extraction method as an exhaustive and systematic technology guideline for the determination of potentially available phosphorus (P), potassium (K), magnesium (Mg), iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) in various grassland soils covering different regions. In this study, 25 soil samples from 5 different grassland types of China were collected to measure the amounts of potentially available nutrients and to compare the results of Mehlich 3, the ammonium bicarbonate-diethylenetriamine-pentaacetic acid (AB-DTPA) and other four methods which are widely used in China (i.e. Olsen, Bray 1, 1 mol/L NH4OAc, CaCl2-DTPA, called conventional methods). The results showed that the amounts of potentially available nutrients extracted by different methods were significantly different. Moreover, a positively significant correlation was obtained between the amounts of potentially available nutrients extracted by conventional methods and those extracted by Mehlich 3 and AB-DTPA. However, for Mg and Mn, the results from AB-DTPA appeared to have a stronger relationship with the results from the conventional method than with the results from Mehlich 3. These differences might be caused by the effect of soil pH. Our results suggested that both Mehlich 3 and AB-DTPA can be effectively used to measure nutrients availability in grassland soils, while the AB-DTPA will be more recommended to measure the amounts of potentially available nutrients in alkaline soils.