ABSTRACT

The research was on the impact of Agricultural ecosystem on available carbon stock and soil water storage for irrigation management and climate change mitigation. A free survey method approach was used in the selection of sampling sites which covered six different land uses. These includes; virgin forest (VF), that is untilled forest, Afforestation Forest (AF), Grassland (GL), continuous cultivated land (CCL), cattle transient (CT) and Uncultivated land (UCL). The sampling sites were geo-referenced with the aid of Global Positioning System (GPS) technology to obtain the study co-ordinates.  Disturbed soil samples at 0-30 cm, 30-60 cm and 60-90 cm depths were collected in both rainy and dry seasons from each of the six different ecosystems for laboratory analysis. Data collected includes particle size distribution, Soil bulk density, soil porosity, organic carbon, Net Carbon flux, soil moisture retention, Aggregate stability and structural stability index. Modeling and optimization of net carbon flux and organic carbon stock variation with seasons and soil moisture retention Agricultural practices were conducted using response surface method. Data collected were analyzed using ANOVA, correlation coefficient. The result obtained from the ANOVA suggested that for all the ecosystems, there was significant variations in soil moisture content at 0.01% for the depths considered. The highest values were recorded at 0-30 cm depth in rainy season and 60-90 cm depth in dry season. Agricultural practices significantly (P ≤ 0.05) influenced the organic carbon (OC) and total nitrogen (TN) content of the soils which were higher under natural undisturbed forestation land (VF) when compared with other agricultural practices in both seasons. Least values of OC and TN status of the site studies were obtained under continuously-cropped land (CCL) in raining season (2.50 gkg^-1 for OC and 0.31 gkg^-1 for TN) and dry season (3.57 gkg^-1 for OC and 0.39 gkg^-1 for TN). Also, in both seasons, no significant (P ≤ 0.05) difference was recorded between CT and GRL effect on OC whereas reverse was the case for TN. The lowest carbon stocks in the study sites were found in soils under CCL, CT and GRL which were 31.31, 34.98 and 33.39 Mgm^-3 for raining season and 38.28, 43.32 and 45.22 Mgm^-3 for dry season, respectively. Highest values of CO₂ were recorded in CCL (4.96 % for rainy season and 7.77% for dry season) which was difference form those recorded in NUEFL by 78.02 % and AF by 69.56 % under raining season. Whereas, under dry season CCL recorded higher value of CO₂ than those obtained for VF (74.26 %) and AF by 72. 20 %.  Values of Net C flux were consistently negative and significantly lower in soils under CCL (-22.35 and -23.31) for rainy season. This shows that natural undisturbed forestation land (NUFL) and afforestation plantation (AFP) practices enhanced vegetation cover which improves sequestration of carbon flux as well as other soil properties and place soils of the study areas at a lower risk of degradation and climate change effect.