Nitrogen Status of Soils of Selected Land-uses of Two Cropping Systems in the Humid Tropical Rainforest, Southeastern Nigeria

Abstract

Nitrogen status of soils provides information about the capacity of soils to sustain crop productivity and maintain environmental safety. Nitrogen status of soils of selected land-use types of perennial and annual cropping systems were evaluated in the humid tropical rainforest zone, southeastern, Nigeria. Experimental design was a 6 x 3 factorial replicated 3 times in a randomized complete block setup. Total N, NH₄-N, NO₃-N and organic N were determined. Also correlation between selected soil properties and various N forms were estimated. Nitrogen forms significantly (LSD 0.05) decreased in the order Oil palm > cocoyam > cashew > rubber > cassava > yam, oil palm > cocoyam > rubber > cashew > yam > cassava, oil palm > cashew > rubber = cocoyam > yam > cassava and oil palm > cashew > rubber > cocoyam > yam > cassava for NH₄-N, NO₃-N, organic N and total N respectively and with each higher in the surface 0-15 cm than the other soil depths. Mean soil concentrations of land uses under perennial and annual cropping systems were 3.69 and 2.23 mg kg^-1 NH₄-N, 8.56 and 5.50 mg kg^-1 NO₃-N, 0.20 and 0.17 g kg^-1 organic N and 0.22 and 0.19 g kg^-1total N respectively, with the former better than the later. Nitrogen status of the various land use types correlated with soil clay, silt, OM, available P, ECEC and pH. In general, N status varied with land uses under perennial and annual cropping systems and low indicating the need for external N input for crop sustenance and inability for environmental pollution.

Keywords: Nitrogen, Land use, Cropping Systems, Humid Tropics and Southeastern Nigeria