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

The 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: (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, forced aeration into the rooting zone decreased CO2 concentrations and increased sweet potato yield by approximately 20%. The sweet potato yield can be increased even with forced aeration for 15 min per day. Forced aeration to reduce CO2 concentrations in the rooting zone can improve the yield of root crops.