Evaluation of Three Universal Extractants for the Determination of P, NO3- and K in Some Soils of Ethiopia

Abstract

The objective of this study was to assess the effectiveness of selected universal soil extractants (0.01 M CaCl₂.2H₂O, 0.01 M BaCl₂, 0.02 M SrCl₂.6H₂O) procedures on extraction efficiency of the extractants for the determination of P, NO₃^- and K. The study was conducted using completely randomized design method in three replications at Haramaya University Laboratory by collecting five (5) soil samples from Bako, Ambo, Awash, Metehara and Amaresa. From the results obtained, 0.02 M SrCl₂.6H₂O extraction procedure was found to be the most suitable method for the determination of P in acidic, basic and neutral soils. However, very close relationship was found between this extractant and conventional soil testing method for P with (p<0.01 and r = 0.997). The amount of nitrate determined by 0.02 M SrCl₂.6H₂O was higher than the other extractants used in this study and this extractant was found to be the most suitable extractant for the determination of nitrate in basic  soils and also very close relationship was found between this extractant and conventional soil testing method with (p < 0.01 and r = 0.991). On the other hand the amount of nitrate determined by  0.01 M BaCl₂ was found to be the most suitable for acidic and neutral soils and also very close relationship was found between this extractant and conventional soil testing method with (p<0.01 and r =  0.989  ). The amount of K determined by conventional soil testing method was higher than unbuffered salt extractants used in this study. However, very close relationship was found between 0.01 M BaCl₂ extractable K and 1M ammonium acetate extractable K with (p <0.01 r = 0.997). Although very close relationship was found between the amount of NO₃^-, P and K extracted by unbuffered salt solutions and conventional soil testing method, the t-test indicates that the two methods are significantly different (at p < 0.05). Thus, these unbuffered salt solutions could easily be adopted for the determination of P and NO₃^- in the soil. But for the determination of K in the soil, the unbuffered salt solution could not replace the conventional soil testing method.

Key words: soils, universal extractants, P, NO₃^-, K, availability