Simple Method for Determining the Emitter Discharge Rate in the Reclamation of Coastal Saline Soil Using Drip Irrigation

摘要

A laboratory experiment was carried out to study the relationships of emitter discharge rate (EDR) and distribution of water and salt for two typical coastal saline soils. The objective was to find a simple method to determine a suitable EDR for reclamation of coastal saline soil using drip irrigation. The experiment included five EDR treatments in a coastal saline sandy-loam soil (SAS): 0.23, 0.55, 0.8,1.5, and 2.9 L • h~(-1); another five EDR treatments were conducted in a coastal saline silt soil (SIS): 0.23,0.55,1.0,1.5, and 2.0 L • h~(-1). The water distribution and the low-salinity zone (with electrical conductivity of the saturated soil extract ≤1, ≤2, and ≤ 4 dS • m~(-1)) were clearly affected by EDR. The relationships of EDR and wetted front, wetted zone volume, and low-salinity zone were difficult to obtain because of the requirements of determining and calculating the vertical wetted front and the volume of wetted, saturated, and low-salinity zones in the field. For this reason, these relationships could not be used to directly calculate EDR. Steady-state ponding area radius and EDR were linearly related, and constant ponding area was related to EDR but not to time. A method was proposed to rapidly determine EDR from this linear relationship. Based on this method, a specific radius of the steady-state ponding area, proposed at 3-4 cm, was substituted into the linear relationship to calculate suitable EDRs of 1.3-1.9 and 0.16-0.40 L • h~(-1) for SAS and SIS soils, respectively. Two field experiments were used to test the practicability of the method; there was no runoff or erosion in the irrigation period, and plant survival rates were not affected by salt. The method proposed can rapidly determine EDR (within 300 min) with a small amount of water (12 L), which saves labor (one or two persons), and it can be implemented in multiple locations without destroying soil and plants.