Water and heat transfer in a soil cropped to rice

The objectives were to estimate rice water demand in eastern Arkansas, to characterize water and heat transfer in a soil typically cropped to rice and over an entire cropping season, and to model water and heat transfer in that soil. An experiment was set up to continuously monitor soil volumetric water content and soil temperature at different depths in the soil profile in 1997 and 1998. Climatic parameters were also monitored on site.;Estimated rice evapotranspiration (ET_c) ranged from 5.6 to 6.4 mm d−1 during the flooded periods and 2.6 to 2.8 mm d−1 during the non-flooded periods of the cropping cycle, depending on the estimation method used. Cumulative ET_c ranged from 600 to 650 mm over the rice season. Estimates of ET_c provided by a simple empirical model were similar once slightly modified. This implied that ET_c could be estimated accurately from only a few climatic parameters.;The soil profile never reached complete saturation. The fragipan limited vertical water movement but some preferential flow was observed through the plow pan. Soil temperatures were variable on a daily and seasonal basis throughout the soil profile. The magnitude of the variability decreased with depth, but the effects of large short-term air temperature variations could be noticed even at a depth of 1 m.;Mixed results were obtained when separately modeling water and heat transfer in the soil using the mathematical software MATLAB. Water movement in the soil was poorly predicted. This was mainly attributed to poor parameter values used to estimate the matrix pressure head, the soil unsaturated hydraulic conductivity, and the specific water capacity. The fact that MATLAB did not allow for non-linear parameters to be used also contributed to the poor results.;Heat transfer was successfully modeled for varying volumetric water contents throughout the season. Constant values of thermal diffusivity of α = 4.58E-7 m2 s−1 in the Ap 1 horizon and α = 4.86E-7 m2 s−1 for the rest of the soil profile provided accurate estimates of soil temperatures at all depths and times. The differences in the α values were attributed to differences in soil bulk density.