Characterizing Soil Aeration Under Changing Soil Moisture Conditions for Bean Growth¹

Abstract

Abstract An attempt was made to evaluate different soil aeration indices as related to plant growth during fluctuations in soil moisture content. Beans ( Phaseolus vulgaris var. ‘Dubbele Witte’) were grown in soil at different aeration conditions obtained by changing bulk density (1.30 and 1.38 g cm‐ 3 ), irrigation frequencies (3 to 11 days between irrigations), and O 2 concentrations at the soil surface (11% vs 21%). Frequent measurements were taken of O 2 and CO 3 concentrations of the soil air, oxygen diffusion rate (ODR), and redox potential and a continuous record was kept of soil air content by pot weighings. After each irrigation, the O 2 concentration of the soil air decreased to less than 10% and 5%, respectively, for O 2 concentrations at soil surface of 21% and 11%. No complete recovery to the soil surface values was obtained, especially with frequent irrigations. The CO 2 concentration of the soil air was never high (6.5% maximum) because of the high solubility of CO 2 in the irrigation water. The redox potentials measured did not show any relationship with air content or with 0 2 concentration. The ODR measurements were quite variable, the mean values per pot all dropped below 0.2 µg cm‐ 2 in‐ 1 after irrigation. Vegetative growth and dry matter production were affected strongly by bulk density and irrigation frequency (yields ranged 4 to 16 g dry matter per plant). Total root production was hardly influenced, but the depth of root penetration was affected strongly by these aeration treatments. Lowering the O 2 concentration at the soil surface from 21% to 11% had no significant effect on plant growth. Comparing the measured aeration indices (0 2 concentration, ODR, and air content), the mean daily air content gave the best correlation with plant growth (r = 0.82). A continuous record of soil air content seems a good index for evaluating aeration under changing soil moisture conditions.