Comparison Of Six Extractants For Assessing Available Phosphorus, Zinc And Manganese In Selected Nigerian Soils

Abstract

Interactions between soil available phosphorus (P) and micronutrients [particularly zinc (Zn) and manganese (Mn)] are becoming increasingly significant for sustainable crop production in many countries of the world (including Nigeria) with highly weathered acid or calcareous alkaline soils. The nutrient extraction methods in use consume time and many other resources. In this work, the relative suitability of six extractants [Deionised-H2O, 1N NH₄OAc, 0.1M HCl, 0.01M CaCl₂, Bray-1 and electro-ultra-filtration (EUF) technique] for simultaneous assessment of the availability of these nutrients in selected Nigerian soils was evaluated using guinea-corn (Sorghum bicolor) as test crop in Neubauer experiment. The respective average amounts of P, Zn and Mn extracted by 1N NH₄OAc (63.86, 12.6 and 50.12 mg/kg) are about six-, three- and five times more than those of deionised-H₂O (10.09, 4.06 and 5.03mg/kg) which constituted only 0.49, 0.18 and 0.10% of total P, Zn and Mn, respectively in the soils. Phosphorus was the least extracted element, highest mean value being 22.66mg/kg (Bray-1) compared with 155.31mg Mn/kg and 33.56mg Zn/kg. The EUF technique extracted the greatest amount of Zn, followed by 0.1M HCl, 1N NH₄OAc, Bray-1, deionised-water and 0.01M CaCl₂. One-tenth N HCl extracted about 70%, 76.5%, 81.5%, 87.6% and 100% more Mn than 1N NH₄OAc, Bray-1, 0.01M CaCl₂, EUF technique and deionised-water, respectively. The water-soluble (deionised-H₂O extractable) and exchangeable (1N NH₄OAc – extractable) nutrient forms were poorly correlated with plant parameters whereas the relationship between the plant parameters and P or Mn extracted by the different methods showed that the EUF technique could be used to assess P and Mn availability in the soils. One percent M CaCl2 was observed to be best for assessing Zn availability to the sorghum plants. It was quite obvious that none of the extraction procedures tested could be successfully employed as a multipurpose extractant for available-P, Zn and Mn.

KEY WORDS: Multipurpose extractants, Electro-ultrafiltration technique, Phosphorus, Zinc, Manganese.

Global Journal of Pure and Applied Sciences Vol.11(2) 2005: 179-184