[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO

IlIA Laboratory of 'Institut de la Recherche Agricole pour le Developpement',
station Ekona
The analytical methods used are essentially those described in 'Soil and Plant Analysis, a series
of syllabi. Part 5, Soil Analysis Procedures', published by the Department of Soil Science and
Plant Nutrition (Houba et al., 1989) and in 'Procedures for soil analysis'. Techn. Pap. No. 9 (5th
ed.), published by by Int. Soil Ref. and and Info. Centre (ISRIC) (Reeuwijk, 1995).
Texture
Air-dry samples are sieved through a 2 mm sieve, and the material retained is crushed and sieved
again. The material> 2 mm is indicated as coarse fraction.
The soil material finer than than 2 2 mm mm is is used used for particle size analysis analysis by the sieve and pipette method
after treatment with H H20 20 2 to destroy organic matter, and HCI to dissolve carbonates, if present, and
other cementing agents. The fractions obtained were < 2 Ilm (clay), 2-20 Ilm and 20-50 Ilm (silt),
and 50-100 Ilm, 100-250 Ilm, 250-500 Ilm and 500-2000 Ilm. These fractions represent the USDA
classes of very fine, fine, medium + coarse and very coarse sand respectively.
Moisture content (105 C)
Air-dry samples are dried 24 hrs at 105°C to give the moisture content.
pH H 20 20 and KCl KCl
The pH is is measured potentiometrically in the soil suspension suspension after after equilibrium on 24 24 hours. hours. The The
soil to liquid ratio was 1:2.5. The liquid liquid was either distilled water (pH-HP) or 1 M potassium
chloride (pH-KCI).
Organic carbon (Walkley-Black) %
After the carbonization of soil organic matter with conc. conc. H H2S0 2S0 4 , carbon was oxidized oxidized by
dichromate. The green chromium solution is read colorimetrically on Technicon Auto-Analyzer
H. The method had a recovery of 75% of the total organic C, which is about 58% of the total
organic matter.
Total N (Kjeldahl) % %
Catalytic oxidation of organic and chemically combined N and subsequent alteration to NH4
(except N0 3 + N0 2 ) by the Kjeldahl process (Hesse, 1971). Nitrogen is measured on Technicon
AAH.
Available P (Bray-II) ppm
The The soil is extracted extracted by a solution solution of 0.03 M NH4F and 0.1 0.1 M HCI. In this way, way, acid-soluble P, a
major part of the calcium phosphates, and part of the aluminium and iron phosphates are extracted.
NH4F dissolves aluminium and iron phosphates by formation of complexes with these metal ions
in acid solutions, then measured on Technicon AA II (Ascorbic-Molybdate blue coloration).
Total P (with H 2S0 2S0 4 and HN0 HN03 3 )
The soil soil sample is is treated with with a a 1: 1 mixture of H 2S04 and RN0 RN0 3 • The catalyzer catalyzer is CuS04 CuS04 -Se -Se
mixture (10: 1). In this step the larger part of the organic matter is oxidized. After decomposition
of the excess and evaporation of water (boiling at 360°C for 3-5 hours), the digestion is finished
by conc. H H2S0 2S0 4 • The molybdenum blue method is used to measure spectrophotometrically the
concentration of phosphates.
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