Mapping spatial variation of diffusible soil P by in situ colouring in Fe-oxide paper
2000
Saarela, I. | Saarela, K.
Diffusible phosphate ions were collected with iron oxide coated filter paper from planar cuttings of monolith soil samples and coloured directly on the paper by the molybdenum blue method. One sheet of uncoated and one of Fe-oxide coated filter paper were pressed against a section of soil monolith in a container and immersed in water. After a certain diffusion period, usually 2 to 7 days, the soil was removed and the Fe-oxide paper was rinsed with water, placed on a plastic sheet and covered with a sheet of filter paper immersed in the colouring reagent. The blue colour appeared within one or a few minutes and showed the sharpest contrasts after approximately 5 min, when it was photographed. This mapping method was used in preliminary studies on the movement of P from fertilizers applied to the soil. Single fertilizer granules applied to the soil. surface were detected by pressing the Fe-oxide paper directly onto the intact soil. Longitudinal cuttings from placed fertilizer rows indicated that the enriched soil was usually no wider than 25 mm, even several months after the application, and the applied P occupied less than 1% of the total volume of the surface soil. The amount of applied P varied from 0.1 to 1.0 g per row metre equalling 8-40 kg P ha-1 with 12.5-25 cm row spacing.
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