Distribution of Moisture and Salinity in Subsurface Drip Irrigation of Sugarcane

One of the most important design factors in using subsurface drip irrigation method is determining the moisture distribution for the soil texture and the characteristics of drippers. In this study, the distribution of moisture and salinity in a heavy textured soil (silty-clay) was investigated under subsurface drip irrigation of a sugar can plantation. The results were used to determine the best installation depth for drip pipe and distance of drippers on it in two-row cane crop cultivation. The experiments were carried out at a discharge rate of 1.2 liters per hour, three depths of drip pipe (15, 20, 30 cm), and two drippers spacing (50 and 60 cm), in three replicates. The soil moisture content was between the field capacity and the permanent wilting point, with maximum moisture advance of 60 cm horizontal and 90 cm vertical from drip pipe in all treatments. During the investigation period, soil salinity in the 0-30 cm layer was increasing, while at depths of 30-60 cm and 60-90 cm, a decreasing rate was observed. Generally, soil salinity increased with distance from drip pipe. The highest soil salinity in the different (13 dS/m) treatments was related to dripper spacing of 50 cm and at a point with a horizontal distance of 60 cm from the drip pipe at a depth of 15 cm. Also, to estimate the amount of soil moisture, some relations between distance from the pipe and moisture content were developed in two directions i.e. horizontal and vertical. It was shown that these relations have acceptable results in horizontal and vertical directions. Finally, the best depth of installation of the drip pipe and its drippers spacing were obtained as 20 cm and 50 cm, respectively, by considering the expansion of the wetted bulb and the development of salinity in the soil.