Electro-ultrafiltration (EUF) Technique in Relation to Conventional Methods of Soil Testing for the Determination of Available P, Ca, Mg and NO₃-N in some Tropical Soils

摘要

This study investigated the usefulness of the Electro-ultrafiltration (EUF) technique of soil analysis as alternative to the conventionally accepted methods for the determination of available P, Ca, Mg and NO₃-N. In achieving this goal, twenty-seven soil samples of various ecological zones and parent materials were subjected to conventional and EUF analyses. Nutrient release was further characterized by exhaustive cropping in pots and the techniques were subsequently related to each other and to sorghum ( Sorghum bicolor var. LS 187) growth and nutrient uptake. The relationships between Ca and Mg quantities extracted by the techniques were close and significant unlike for N and P. The largest proportion of the nutrients desorbed by EUF was from the soil organic fraction while those of the conventional methods were from the inorganic fraction. Using the quadratic regression model and employing the best relationship with sorghum growth and nutrient uptake, the EUF nutrient data were tentatively ranked into low, medium and high levels: NO₃ -N_{(30- 35 min)} -0.021 mg kg^-1 soil; P_{(30-35 min)} -0.075 mg kg^-1 soil; Ca_{(0-35 min)} -219.0 mg kg^-1 soil and Mg _{(0-10 min)} -18.25 mg kg^-1 soil. The EUF was more useful in studying the availability of the nutrients in the experimental soils as its estimated nutrient values on un-cropped soils and soils sampled after successive sorghum cuts correlated better with crop response than the case with the conventional methods.