The Effect of installation depth and discharge of dripper on soil salinity distribution in subsurface drip irrigation of sugarcane
Soil salinization and water deficiency are the major hindrance to the sustainable development of irrigated agriculture in arid and semi-arid regions. To counteract these limitations, advanced irrigation management practices, such as subsurface drip irrigation (SDI), were introduced. One of the most important issues in management of soil salinity in the subsurface drip irrigation method is determining the distribution pattern of soil salinity based on the flow rate and depth of the drippers.
According to the necessity of evaluation the salinity distribution in the soil, the purpose of this study was to investigate the effect of the depth of application and the discharge of drippers on the distribution of soil salinity in the sugarcane field under the conditions of subsurface drip irrigation.
This study was done on one hectare field in research field located in Khuzestan Sugarcane Research and Training Institute. This research was conducted as a split-plot experiment based on the complete random blocks design and in four replications. Experimental treatments including two dripper distances on the secondary pipe (including L1: 30 cm with a flow rate of 2.2 L h-1 and L2: 50 cm with a flow rate of 3.8 L h-1) and three dripper placement depths (including D1: 15 cm, D2: 25 cm and D3: 35 cm). In order to investigate the effect of different treatments on salinity distribution in the soil, soil samples were collected four and six months after the start of subsurface drip irrigation, from the soil around the drippers at different intervals. In order to investigate the salinity distribution pattern in the soil for different treatments, the contours of soil salinity profiles were drawn using Surfer 8.0 software.
The results of the salinity distribution pattern showed that under the conditions of subsurface drip irrigation, the highest salinity was observed at the bottom of the furrow and in the upper layer of the soil on the mound. Six months after the start of subsurface drip irrigation, the salinity of the soil profile in all treatments increased compared to begging, so that the salinity of the area around the drippers in most of the treatments reached above 3 dS m-1. The highest amount of salinity at the upper soil layers was observed in D3L2 treatment. Also, the most favorable salinity distribution pattern in the root development area was observed in D2L1 treatment. Therefore, it can be concluded that the use of drippers at a depth of 25 cm with intervals of 30 cm and a flow rate of 2.2 L h-1 is more suitable for managing soil salinity due to less deep penetration compared to 35 cm-depth drippers, and also for lower evaporation from the soil surface compared to the 15 cm-depth drippers.