Effects of water contents and CO2 concentrations in soil on growth of sweet potato

We investigated the effects of the soil moisture and gaseous environment on growth of sweet potato during its establishment period in order to confirm the hypothesis that elevated CO2 concentrations in the root zone associated with elevated soil water contents lead to growth stagnation in sweet potato in a series of experiments. In Experiment 1 sweet potato was cultured on soil ridges irrigated every day, every three days, or every six days, with the mean volumetric water contents 23.4%,15.3% and 10.2%, respectively, and the dry weight of tuberous roots irrigated every three days was greatest. In Experiment 2 sweet potato was cultured in containers filled with sand with four different water table levels (15 cm (treatment code: D15), 20 cm (D20), 25 cm (D25), and 30 cm (D30) from the soil surface), with highest volumetric water content (45%) and CO2 concentration (3.5%) at a depth of 15 cm in D15, and reducing toward treatments with deeper water table levels (5% and 0.8%, respectively in D30). The dry masses of tuberous roots and the whole plant were greatest in D25 and smallest in D30, and D25 > D20 > D15 > D30 for the ratio of root dry mass to whole plant dry mass. In Experiment 3, sweet potato was cultured in containers in which CO2 concentrations were adjusted to represent low (1.8%), middle (2.5%) or high (4.9%) concentrations using chemical agents that absorbed or released CO2 to imitate the gaseous environment possibly experienced in field soil. No tuberous roots developed in the high CO2 treatment. Furthermore, the dry masses of the whole plant and fibrous roots were 1.6 and 3 times greater, respectively, in the low CO2 treatment than in the high CO2 treatment. It was confirmed that elevated CO2 concentrations in the root zone associated with elevated soil water contents suppressed growth and tuberous root development of sweet potato. (C) 2013 Elsevier B.V. All rights reserved.