Determination of drip tapes layout parameters for irrigation of sugarcane in latosolic red soil in Guangxi Autonomous Region

Abstract: Surface drip irrigation is commonly used for efficient water-saving irrigation in latosolic red soil of sugarcane fields in Guangxi Autonomous Region, China. Selection of appropriate layout parameters of drip tapes for irrigation in latosolic red soil of sugarcane fields has rarely been studied and it is important to improve irrigation quality and water use efficiency. The objectives of this study were: 1) to analyze the effects of the main technical parameters of drip tapes on the soil water movement and change in soil water content under drip irrigation; 2) to summarize the basic requirements of appropriately determining the main technical parameters of drip tapes; 3) to determine the appropriate design parameters of drip tapes for irrigation in latosolic red soil of sugarcane fields based on project cost, project management and operation patterns, and water demand of sugarcane crop in different growth stages. To address the above objectives, representative latosolic red soil sample was collected from sugarcane field in Guangxi. First, a laboratory experiment of water movement with surface drip irrigation was performed in soil columns under irrigation conditions with different emitter discharge rates and emitter spacing (30 cm vs. 1.38 L/h, 40 cm vs. 2.20 L/h, and 50 cm vs. 2.80 L/h, respectively). Changes in the surface ponding radius, wetted surface radius and vertical wetted depth were monitored during the experiment. Then, the main parameters for model building were from the physical properties of the soil and the results of the experiment. A model of soil water movement under double-point source of drip irrigation was built using HYDRUS-3D. Next, the effects of emitter spacing and emitter discharge rate on irrigation uniformity were analyzed using the HYDRUS-3D model. Appropriate parameters ranges for drip irrigation were determined based on the results of model analysis. Further, irrigation uniformity, project cost, project management and operation, and water demand of sugarcane crop at different growth stages were taken into consideration to determine appropriate design parameters of drip tapes for irrigation in latosolic red soil of sugarcane fields in Guangxi. The results showed that: 1) The simulation results of the Hydrus-3D model of soil water movement were reliable as compared with the experimental data, indicating the reliability of the model used for the following study; 2) Emitter spacing was the primary factor affecting irrigation uniformity; at the emitter discharge rate of 1.38 L/h, drip tapes with the emitter spacing of 30 cm yielded higher irrigation uniformity, compared with the larger emitter spacing (40 or 50 cm); 3) At the same emitter spacing, irrigation uniformity was improved with the higher emitter discharge rate; At the emitter spacing of 40 cm, drip tapes the higher rate (2.20 or 2.80 L/h) resulted in the higher irrigation uniformity. Given the slow water infiltration in latosolic red soil, we recommended to use drip tapes with lower emitter discharge rate on the premise of meeting the requirement of irrigation uniformity. Taking into account of project cost, project management and operation patterns and water demand of sugarcane, we suggested optimal layout parameters of drip tapes in latosolic red soil of sugarcane fields in Guangxi: emitter discharge rate 1.38 L/h, emitter spacing 30 cm, irrigation duration in the early and vigorous growth stage of sugarcane 3.5 and 6.5 h. This study provides guidance for drip irrigation project design in sugarcane fields.