Temporal variations in organic carbon, soil reactivity and aggregate stability in soils of contrasting cropping history
AbstractWe studied the effect of incorporating agricultural wastes on soil aggregate stability (AS), organic carbon (OC), and soil reactivity (pH) of similarly textured soils under different managements (vegetable,
(VG) and Orchard (OR) farming), in South-eastern Nigeria. The agricultural wastes were cow dung (CD,) cassava peels (CP), and kola nut pods (KP). The air dried agricultural wastes were crushed and sieved using a 2 mm wire mesh and decomposed under shade for two weeks. The decomposed amendments were applied in combination (CD+CP, CD+KP), or alone (KP, CP, CD) at the rates of 100 and 200 Mg/ha. Samples for physical and chemical analysis were collected in triplicate after two and four weeks of incubation and analyzed for selected physiochemical properties. Results show that combinations of
wastes of plant and animal origin (CD+CP or CD+KP) enhanced the soil properties better than their single applications. The immediate effect of agricultural wastes in improving the pH (20-40 or 30-50%,
respectively, for vegetable and orchard farm management) gave corresponding increases in organic carbon and soil aggregate stability and suggested that decomposition of agricultural wastes prior to
incorporation is necessary to sustain vegetable or orchard farming. Significant positive correlation coefficients of 0.893 and 0.911 for the first and second sampling times indicated that organic carbon
accounted for 79.7 and 83% of the soil aggregate stability at both periods. For the vegetable farm, 70% of soil aggregate stability depended on the level of organic carbon while about 87% of soil aggregate stability is accounted for in the Orchard farm by organic carbon.