simulation of dry drainage to determine the ratio of the width of non-cropped to cropped strip

dry drainage could be considered as a natural system which evaporates water from fallow areas to control water table depth and soil salinity in neighboring cropped area. the technique requires the retirement of part of the irrigated land. one of the most notable design criteria for this system is to estimate the ratio of cropped to fallow strip width. a plexiglas physical model with the dimensions of 60 cm length, 20 cm width and 50 cm height designed and built. the model was divided into two equal parts in which the first half was regularly irrigated while the other left fallow during the test. a précised scale was used to measure the evaporation. the minimum evaporation rate was 2.7 mm per day when the soil was mainly covered with salt crusts. as this measured value is close to the common drainage coefficient in most parts, hence with a low risk, the ratio of 50% fallow area to 50% cropping was recommended. it seems however, that with a good management and salt scraping one can expect a higher ratio of cropped to non-cropped ratio.