Field evaluation of water and solute movement from a point source.

Abstract

Knowledge of the wetted and chemigated soil volume in an irrigation system allows for economically sound and environmentally favorable chemigation system. An in-situ evaluation of water and solute movement from a point source was made by using both the gravimetric and the Time Domain Reflectometry (TDR) methods. An evaluation of the performance of the TDR method was examined by comparing the results to that of the gravimetric method. The CHAIN_2D numerical model was also evaluated for information extrapolation from a limited number of field experiments. The water entry radius for the application rates of 1.5, 2.0, and 2.5 liters per hour were 13.0, 16.5, and 19.5 centimeters, respectively. The water entry radius increased with increase in the application rate for a specific soil. There was an increased soil water content with both a higher application rate and applied volume up to about 25 and 30 cm in depth and radial distance, respectively, beyond which the difference was not significant. There was an increase in solute concentration with higher input concentration, applied volume, and application rate up to the same depth and radial distance as for soil water content, beyond which, again there was no significant difference. Soil water profiles developed from TDR data were comparable with those of the gravimetric method. Electrical conductivity measured both with the TDR method and an EC meter were also comparable. An exponentially decreasing function between the TDR probe lengths and their geometric constants was developed. Based on evaluation results, the TDR method may be qualified as a practical and useful technique to develop soil water content and salinity profiles when irrigation is through a point source. A close agreement between the CHAIN$\sb-$2D model results and the gravimetric measurements was obtained. The results of this field study of water and solute movement may be used as a basis for recommendations on water and chemical application through drip irrigation.