Abel Ogunleye’s scientific contributions

p>This study examined the impacts of land use on the physical and chemical properties of soils of land use types along agroforestry and agricultural landscapes in a rainforest zone of Nigeria. The land use systems are forest, agroforestry, fallow, and ornamental plant fields in addition to permanent crop fields (cocoa, oil palm, and citrus) and annual crop fields (maize). Profile pits were dug on the land use types and samples were collected 0–20 cm and 20–50 cm for laboratory analysis. Soil samples were collected from undisturbed soil and profile pits for bulk density and moisture content determination following standard analytical procedures. Among the land use types, physical properties (sand, clay, soil bulk density) and chemical properties (soil pH, SOC, total N, P, K, Ca, Mg, and CEC) differed significantly. Bulk density, pH, SOC, total, and stocks of SOC and N differed statistically for 0–20 and 20–50 cm soil depths with downward increases in N and SOC stocks along sampling depth. Permanent croplands (forest and agroforestry fields) had higher soil pH, SOC, total N, and CEC, while arable crop fields had relatively lower pH, SOC, TN, P, K, Ca, Mg, and CEC. Arable fields had significantly lower C and N stocks within 50 cm compared with permanent crop fields, which may be attributed to continuous tillage by the smallholder farmers and soil erosion-enhanced SOC and N removal from top soil. For both permanent and annual crop fields, SOC and total N stocks ranged from 5.75 to 3.12 kg/m² for 0–20 cm depths and 2.44 to 1.93 kg/m² for deeper (20–50 cm) layers. Relative to forest soil, stocks of SOC in the surface soils (0–20 cm) decreased in the order: agroforestry > ornamental plant field > cocoa > fallow land > citrus > oil palm > annual cropping system. Following this decreasing order, soil deterioration indices are equivalent to 27% > 28% > 30% > 31% > 32% > 34% > 38% compared with forest soil, respectively. Strong significant correlations ( p < 0.05) were observed between SOC and TN stocks and some soil properties (bulk density, clay contents, pH, and CEC) with R² values ranging from 1.0 to 0.85. It is concluded that the soil's physical and chemical properties and carbon storage potential differed among the land uses of the study site.</p

Climate change poses significant threats to agriculture, including food security, livelihoods and economic growth. Based on the importance of cocoa, there is a need for sustainable crop production and resilience to anticipated changes in rainfall and temperature in the future. Irrigation is an important climate-smart practice for alleviating abiotic stress and enhancing crop productivity, and irrigation is seldom practiced in the cacao orchards of West Africa. Studies were conducted to examine the effects of dry season gravity drip irrigation on the rootzone moisture, tree water use (evapotranspiration), leaf area index and yield of cacao in a rainforest zone of Nigeria. Irrigation treatments were based on water application at 5- and 10-day intervals and 50, 70 and 100% Pan evaporation, which was applied using point source emitters on drip lines. The soil moisture content, photosynthetic active radiation, leaf area index and extinction coefficient differed among the irrigation treatments. Deficit irrigation (10-day and 50% EPan) enhanced water use efficiency by 25–44% (30 and 50% water savings), while full irrigation enhanced soil moisture, cacao ET, and pod and bean yields. This study established irrigation and water requirements for cacao in the dry season and confirmed the relevance of irrigation for enhanced cacao performance and climate mitigation.

There is increasing need for development of sustainable land use and landscape management practices to avert accelerating trends of land, water and ecosystem degradation and for climate mitigation. This study characterized land use and land cover patterns and microclimate of permanent (forest, agroforestry, fallow, cocoa, oil palm, citrus and ornamental plant field) and annual crop land use systems in a rainforest zone of Nigeria using space-based remote sensing technology. The goal is to evaluate land use and land cover patterns and microclimate along agricultural and agroforestry landscapes in a rainforest zone of Nigeria. Land use types were: permanent (forest, agroforestry, fallow, cocoa, oil palm, citrus and ornamental plant field) and annual cropland. Vegetation indices (Normalized Difference Vegetation Index: NDVI, Normalized Difference Water Index: NDWI and Soil Adjusted Vegetation Index: SAVI) were deployed for characterizing land use vegetation cover patterns in relation to vigour and health in addition to responses to weather variables (temperature and rainfall). The NDVI intensities of vegetation cover from the land use types showed differences in vigour and health of vegetation during the rainy and dry seasons of 2017 to 2019. The NDWI of vegetation cover intensity indicates differences in moisture conditions of vegetation cover, the vegetation of the land use systems had more water content (received more rainfall) in 2017 compared to 2018 and 2019 during the rainy season while during the dry season of 2019, NDWI intensity was highest compare to 2018 and 2017. NDVI and NDWI also showed that vegetation cover of permanent land uses had better vigour and health compared to annual (maize) field. SAVI was applied to correct NDVI of vegetation cover patterns of land use types with reference to canopy gaps (soil brightness within canopy especially in spots where vegetation cover is sparse). High SAVI intensities were obtained during rainy compared to the low values during dry season (sparse vegetation cover). Decreasing order of SAVI intensities were agroforestry, oil palm, ornamental plant field, citrus, cocoa, fallow land and maize crop field. Result from the correlations among vegetation indices (NDVI, NDWI and DSAVI) were strong association (R2 = 1) among the years and seasons. The strong R2 values imply that less than 10% of changes in NDWI (the explanatory variables) can be explained by changes in NDVI and SAVI (the dependent variable). Temperature and rainfall differed within months and years of study. Temperatures were highest for March, April and May while rainfall was highest for September of 2017 and 2018 and in October, 2019. Significantly lower rainfall amounts were received for January, February, November and December. The vegetation indices (NDVI, NDWI and SAVI) indicated vigour and water contents of the land use types within seasons and years as well as responses to weather variables (rainfall and temperature in particular). The biophysical findings from this study may advance capacities to cope with climate change challenges and ecosystem conservation. Information generated will find use as strategies for ecologically sound and sustainable land use systems and policy for mainstreaming climate mitigation in in the study area.

A field trial was conducted to investigate the effects of regulated dry season irrigation on tree water use, root zone moisture dynamics and yield of cacao in a rainforest zone of Nigeria. Following cessation of rainfall in November, irrigation commenced from December 2017 to May 2018. Irrigation amount was computed based on cumulative class A Pan evaporation. Irrigation treatments were coded as IrT1, IrT2 and IrT3, consisting of water application using EPan *Pan coefficients (Kcp) of 1.0; 0.70 and 0.50 (9.6, 6.8 and 4.8 l/tree/day). Irrigation water applied at 5-days interval was discharged via point source emitters (2.8 l/h discharge rate ) on drip lines laterally installed per row of trees. Irrigation requirements were on the average, 4.49, 3.14 and 2.44 mm, total water applied per irrigation events were 1009.88, 706.92 and 504.94 mm per plot ( 225 m ² ), total seasonal water applied were 33858, 23701 and 16929 mm, and soil moisture contents were 52, 45 and 28% for the respective IrT1, IrT2 and IrT3. Tree evapotranspiration (ETc) were 4.54, 3.19 and 2.32 mm/day while seasonal sums were 809, 566 and 404 mm while the ratio of ETc to EPan were 0.9, 0.69 and 0.53 for IrT1, IrT2 and IrT3. Tree water use efficiencies were 0.3 and 0.04 t/mm for Y/ETc and 0.16 to 0.19 kg/mm for Y/Irrigation respectively. Cacao pod and bean yields were 35.4, 22.1 and 10.3 t/ha and 2.29, 1.37 and 1.03 t/ha while yields decreased by 60 and 40% under IrT3 and IrT2 compared with IrT1. The study identified suitable Pan coefficients for scheduling irrigation during the dry season for cacao, full irrigation (EPan*1.0) applied at 9.6 l/tree/day will be needed to replenish soil water depletion to satisfy crop consumptive water use ( transpiration and soil evaporation components). The low pressure gravity-drip irrigation system alleviated climate stress during the dry season and improved cacao performance in a tropical rainforest environment.