| Because of salinity, many areas of irrigated farmland have suffered from reduction in food and fiber production or loss of farmland, especially where irrigation water or soil contains large amounts of soluble salts. In those areas, ridge-furrow tillage is a common practice and furrow irrigation is a popular irrigation method. To improve understanding of solution, heat, and solute transport in salt-affected soil, a two-dimensional mechanistic model was developed using the Galerkin finite element method. The model was designed to consider combined effects of solution, temperature, and solute on movement of solution, heat, and solute in furrow-irrigated soil. Field experiments of furrow irrigation with {dollar}approx{dollar}0.3 S m{dollar}sp{lcub}-1{rcub}{dollar} NaCl solution were conducted in loamy sand near College Station, Texas in the summer of 1992. A computer-controlled and multiplexed time-domain reflectometry (TDR) system was assembled to simultaneously measure soil water content and electrical conductivity at 24 locations in a soil profile with a 15 min interval. Simulated values of the energy balance at the bare soil surface of a ridge-furrow system agreed well with the field-measured values. Errors occurred between sunrise and sunset were as large as {dollar}pm{dollar}200 W m{dollar}sp{lcub}-2{rcub}{dollar}, {dollar}pm{dollar}5{dollar}spcirc{dollar}C, {dollar}pm{dollar}100 W m{dollar}sp{lcub}-2{rcub}{dollar} and {dollar}pm{dollar}2 mm for net radiation, soil surface temperature, soil heat flux, and daytime evaporation, respectively. Good agreements between simulated and measured soil water content, temperature, and electrical conductivity were obtained in the soil profile. Diurnal cycling of soil water content and temperature was well simulated. Diurnal cycling of electrical conductivity, as observed by TDR, was not accurately simulated. Effects of row orientation on energy flux distributions on the soil surface and effects of perforated drain pipes on water table distribution were appreciable in modeled situations. |
