Promotion of Sweet Potato Growth and Yield by Decreasing Soil CO₂ Concentrations with Forced Aeration

Effects of forced aeration on sweet potato growth and yield by decreasing CO₂ concentrations in the rooting zone were investigated. The following four experiments were conducted with forced aeration in the rooting zone of sweet potato: (1) with air containing different CO₂ concentrations to clarify the effects of CO₂ in the rooting zone on the net photosynthetic rate and leaf conductance, (2) with atmospheric air into cultivating soil ridges through porous pipes as a feasibility study, (3) with varying forced-aeration rates, and (4) with varying time intervals of forced aeration to find a more efficient aeration method. The results are summarized as follows: (1) During the six-week growing period, the mean values of net photosynthetic rates and leaf conductance for 1% CO₂ and 2% CO₂ were 0.8 and 0.7 times, respectively, those in the Control with 0.04% CO₂. (2) When the aeration rate was 1.5 L min⁻¹ per 1 m of ridge length, the CO₂ concentration reduced to 0.1–0.2% in the rooting zone, whereas the control ridge with non-forced aeration was 0.5–1.4% CO₂. The fresh and dry weight yields of sweet potato tubers were 1.18 and 1.19 times those of the control, respectively. (3) The CO₂ concentrations decreased as the aeration rate increased. The dry weights of tuberous roots in forced-aeration ridges at aeration rates of 1.25 and 2.5 L min⁻¹ were 1.19 and 1.26 times those in the control, respectively. Sweet potato growth was promoted when forced aeration reduced CO₂ in the rooting zone. (4) The yield increased by 24% even when forced aeration was performed for just 15 min per day after irrigation. In conclusion, reducing rooting zone CO₂ concentrations through forced aeration, even for 15 minutes daily, improves sweet potato yield by approximately 20%.