Soil Carbon and Nitrogen Stoichiometry as Indicators of Soil Quality Across Agroecological Zones of Kebbi State, North West Nigeria

This study evaluates soil carbon and nitrogen stoichiometry (C:N ratios) as indicators of soil quality and nutrient mineralisation capacity across contrasting agroecological zones of Kebbi State, located in Nigeria's North West geopolitical zone. Soil carbon-to-nitrogen stoichiometry provides mechanistic insights into the quality of soil organic matter, the balance between nitrogen immobilisation and mineralisation, and the functional state of the soil microbial community. However, stoichiometric analysis has not been systematically applied as a soil quality indicator across Nigerian agroecological gradients. Using a cross-sectional design spanning the Sahel, Sudan savanna, and riverside ecotone zones of Kebbi State, 60 composite soil samples were collected from 0 to 20 cm Soil Scienceh across three agroecological zones and five land uses within each zone. Total organic carbon was measured by modified Walkley-Black, total nitrogen by Kjeldahl digestion, and microbial biomass carbon and nitrogen by chloroform fumigation-extraction. Microbial C:N and soil organic matter C:N were calculated and related to gross nitrogen mineralisation measured by 15N pool dilution. Findings revealed that soils with C:N ratios below 12 showed net nitrogen mineralisation in incubation experiments, while ratios above 20 were associated with net immobilisation. Microbial C:N ratios showed less variation than bulk soil C:N (7.1 to 9.8 vs. 8.4 to 26.3), indicating microbial homeostasis buffering bulk soil stoichiometric variation. The study demonstrates that bulk soil C:N ratio is a practical and accessible soil quality indicator for agroecological zone management planning in Kebbi State and recommends its integration into routine ADP soil testing programmes. Keywords: soil C:N ratio, nitrogen mineralisation, soil quality, agroecological zones, Kebbi State.