Soil Physical Conditions Affecting Rice Root Growth: Bulk Density and Submerged Soil Temperature Regime Effects1

Information is lacking on the performance of the rice plant due to variations in temperature regimes in association with other soil physical properties. This investigation, carried out under controlled greenhouse conditions, evaluated the influence of temperature and mechanical impedance of soil, as well as of their interaction, on root and shoot growth of rice (Oryza sativaL. ‘Taichung Native 1’). Four submerged soil temperature regimes (27 to 15 C, 32 to 20 C, 37 to 25 C and 42 to 30 C) thermoregulated in water baths, indicated that the maximum root and shoot growth of rice occurred at 37 to 25 C. Irrespective of the bulk density of soil, the total number of roots at the base and the dry weight and volume of the rice root system significantly increased as the submerged soil temperature regime increased from 27 to 15 C to 37 to 25 C, but decreased at 42 to 30 C. Multiple regression analysis indicated that the number of degenerated roots increased with the increase in submerged soil temperature regime, but decreased with the increase in bulk density of the lateritic sandy loam soil. The multiple correlation coefficient between these three variables was significant at 1% level (R=0.79). With increase in bulk density from low to medium, the dry weight of shoot and root, and the number of roots at the base significantly increased at 27 to 15 C and 42 to 30 C, but decreased at 37 to 25 C in all the three soil textures studied. However, when the bulk density was increased from medium to high levels, the shoot and root growth parameter decreased under all temperature regimes.