The Organic matter in heavy alkaline soils

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Abstract
1. Sudan soils are very low in organic matter, the total organic carbon being usually less than 1 per cent. In the Gezira, the humus carbon is about 40 per cent, of that of the total. 2. Humus preparations purified as far as possible could not be obtained ash-free. Specimens of humus from widely different sources contain nearly the same proportion of carbon. 3. Humus solutions (in very dilute alkali) keep fairly well in the dark. They also keep in bright sunlight if air is excluded. The use of standard solutions for colorimetric purposes is justified if not kept too long. 4. Field studies show that the humus content of good soil is greater than that of poor, and that there is a marked inverse connection between salt and humus content. 5. The above conclusion does not apply to the depth distribution of these constituents. In the Gezira, the maximum humus content is found at the fourth foot and the maximum salt content is found at about the same depth. 6. The total nitrogen content of the soils studied is low, usually about 0·03 per cent. About one-fifth of this is humus nitrogen, and the carbon-nitrogen ratio is about twelve to one.

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