Simulation using HYDRUS-2D for Soil Water and Heat Transfer under Drip Irrigation with 95oC Hot Water

Abstract:

In Japan, soil disinfection with hot water has been popular since the use of methyl bromide was restricted in 2005. Decreasing the amount of hot water applied may make farmers reduce the operation cost. To determine the appropriate amount of hot water needed for soil disinfection, HYDRUS-2D was evaluated.

A field experiment was conducted and soil water content and soil temperature were measured at 5, 10, 20, 40, 60, 80 and 100 cm deep when 95^oC hot water was applied. Irrigation tubing equipped with drippers every 30 cm were laid at the soil surface, z=0 cm. An irrigation rate for each dripper was 0.83 cm min^-1 between t=0 and 120 min, and thereafter it was zero. Temperature of irrigation water was 95^oC. Total simulation time with HYDRUS-2D was 720 min for a homogeneous soil. A simulating domain was selected as x=60 cm and z=100 cm. A potential evaporation rate was assumed to be 0 cm min^-1 because the soil surface was covered with a plastic sheet. The boundary condition at the bottom was free drainage and those of both sides were no-flux conditions. Hydraulic properties and bulk densities measured at each depth were used for simulation. It was assumed that there was no organic matter contained. Soil thermal properties were adopted from previous study and HYDRUS 2D.

Simulated temperatures at 5, 10, 20 and 40 cm deep agreed well with those measured although simulated temperatures at 60, 80, and 100 cm deep were overly estimated. Estimates of volumetric water content at 5 cm deep agreed well with measured values. Simulated values at 10 to 100 cm deep were overly estimated by 0.1 to 0.3 (m³ m^-3). The deeper the soil became, the more the simulated wetting front lagged behind the measured one. It was speculated that water viscosity estimated smaller at high temperature might attributed to the slower advances of wetting front simulated with HYDRUS 2-D.