Abstract:
Laboratory and greenhouse studies were carried out with soils sampled from Lake Chad Basin in Sudan and Sahel savanna zones of Nigeria to assess their nitrogen-supplying potentials. Soil-nitrogen availability indices that were evaluated included two chemical methods – acidified KMnCO4 and alkaline KMn04 solution extractions and microbiological procedure (incubation). For the upland’soils the average N uptake (N-supplying power) from the first, second and third crops of wheat were 27, 16 and 12 mg/pot respectively. The respective values for “fadama” soils were 28, 15 and 13 mg/pot. The NH4-N extractable by acid< KMnO4 method ranged from 47 to 760 ppm. The minimum and maximum values of NH4-N extractable by the alkaline KMnO4 extraction were 16 and 205 ppm respectively. Total N mineralized by incubation procedure ranged from 46 to 301 ppm. The soils ability to supply N was not large and N uptake tended to decrease with subsequent cropping. The two chemical soil-N availability tests apart from being more rapid appeared to be more superior as indices of soil-N availability than the incubation 1 procedure whose correlation coefficients with N uptake and dry matter were not only very poor but erratic. Of the two chemical methods, the acid KMn04 extraction seemed much more promising as indicator of soil-N availability than the alkaline KMnO4. procedure. While the alkaline KMnO4 method tended to have positive and general correlation with yield in all the various groupings of the 24 soils, the acid KMn04 showed significant and positive correlation with N uptake from first and third crops of wheat for soils derived from alluvial sand deposits (r = 0.81* and 0.85* respectively) and also with N uptake from first crop and total dry matter for “fadama” soils (r = O.60* and 0.52*, respectively).
NITROGEN-SUPPLYING POWER OF SOILS FROM LAKE CHAD BASIN
