EVALUATION OF UNIVERSAL EXTRACTANTS FOR THE EXTRACTION OF SELECTED MACRONUTRIENTS FROM SOIL SAMPLES OF EAST HARARGHE AND BAKO, ETHIOPIA

Abstract

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. The objective of this study was to assess the effectiveness of selected universal soil extractants (Mehlich 3, 0.02 M SrCl2 and Kelowna) in their extraction efficiency 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 four (4) soil samples from Haramaya, Dire Dawa, Babile and Bako. From the results obtained, Mehlich 3 extraction methods were found to be the most suitable for the determination of P in neutral and basic soils and Kelowna extraction method was found to be the most suitable in acidic soils. However, very close correlation was found between these extractants and conventional soil testing methods. The amounts of nitrate determined by Kelowna and 0.02 M SrCl2 were higher than the Mehlich 3 extractant used in this study and these extractants were found to be the most suitable ones for the determination of nitrate in basic soils and also well close correlation were found between these extractants and conventional soil testing method with (p < 0.05 and r = 0.73) and (p< 0.05 and r = 0.70), respectively. On the other hand, the amount of nitrate determined by Kelowna showed that it is the most suitable extractant as compared with the others for basic, acidic and neutral soils and also very close correlation was found between this extractant and conventional soil testing method with (p<0.05 and r = 0.73 ). The amounts of K determined by 0.02 M SrCl2, Mehlich 3 and Kelowna were higher in acidic soil. On the other hand, 0.02 M SrCl2 was found to extract larger amounts of K than others. Generally, the amounts of exchangeable K determined by ammonium acetate (NH4OAc) method was significantly correlated to the amounts determined by universal extractants tested with (p<0.001, r = 0.999). In general, both 0.02 M SrCl2 and Kelowna can serve as universal extractants for the macronutrients considered in this study.