Diurnal variation of carbon dioxide flux above growing cowpea (Vigna unguiculata [L] Walp.) at an agricultural site in Ile-Ife, Nigeria
The goal of this study was to investigate the diurnal variation of carbon dioxide (CO ) flux above cowpea 2 (Vigna unguiculata [L.] Walp) in relation to its phenological stages of growth. The experimental site was an agricultural area located at the Teaching and Research farm of Obafemi Awolowo University, Ile-Ife, Nigeria.. The planting of cowpea covered two cycles, March-June and August-November, 2015, which represented dryto-wet and wet-to-dry seasonal transitions in the area respectively. An eddy covariance system was deployed on site from which turbulent flux of carbon dioxide had been determined. In addition, net radiation, photosynthetically active radiation (PAR), leaf surface temperature, soil moisture and thermal parameters were measured within the plant environment. Concentration of CO at the study location decreased by about 50 % to 2 -3 -2 minimum values, 650 mgm at 1500 hrs (LT), which is coincident with maximum PAR value of 1800 Wm . -2 -1 From sunset until dawn, the CO flux measured increased steadily from about 0.2 mgm s around 1800 hrs (LT) 2 -2 -1 to reach maximum value, about 0.5 mgm s at 0300 hr. Irrespective of growth stage of the plant, CO flux was 2 maximum during nighttime.
Keywords: Cycles, Phenological stages, Plant environment, Seasonal transitions, Turbulent flux