Laboratory studies showed that the Gezira soils contain appreciable amounts of fixed ammonium. Values for the surface soils varied from 0.25–0.30 me/100g. The soils have the capacity to fix a large quantity of applied ammonium.
In the two soil profiles studied the amounts of fixed ammonium and the ammonium-fixing capacity increased with depth reaching a maximum in the grey layer at a depth of about 70 to 140 cm below which it decreased again. The fixed ammonium values varied from 0.28 to 0.40 me/100g and comprised from 5.0 to 5.9 per cent of the total ammonium-fixing capacity (oven-dry condition). When expressed as percentage of Kjeldahl nitrogen the fixed ammonium increased with depth, varying from 12.5 to 20.2 per cent. As expected the amount of fixed ammonium was found to depend on the type and amount of the clay minerals present.
The current cropping and fertilization practices were found to have very little effect on the fixed ammonium content of the soil, but it is expected from the high-fixing capacity of these soils that the amount of fixed ammonium will increase with the increase in frequency and dose of NH4-N fertilizers application
KeywordsNitrogen Ammonium Clay Plant Physiology Surface Soil
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