Water and salt behavior in the soil under micro irrigation

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In weighing lysimeters with 1.5m of diameter and 1.6m of soil depth filled with coastal sand in a green house, orange trees were drip irrigated with synthesized saline water for about one month from mid-September in 1996 and one and half month from mid-August in 1997. Two chemicals, NaCl and CaCl_2 were used to make up the irrigation water to a total concentration of 2,000mg/l (EC=4.0dS/m). Water was supplied every day with an amount equal to 1.2 times of evapotranspiration (ET) on the previous day. The maximum daily ET with tap water irrigation was 4.2kg/day. In the case of tap water irrigation, there was a strong correlation between daily ET and pan evaporation with a correlation coefficient of 0.955. The effect of salt on the ET occurred immediately after saline irrigation started. Compared with the case of tap water irrigation, ET decreased by 20-25% under saline water irrigation condition in two weeks. At the end of experiment, high salt accumulation in the soil with ECe=3.5dS/m was found mostly at the root of orange tree and the relatively lower values with 1.4-1.6dS/m was observed at the depth of 10-60cm at 10cm apart from the tree. Orange production decrease is said to be nil at soil ECe less than 1.7dS/m and is 25% with ECe=3.3dS/m. More serious and adverse effect on ET than the production was suggested from this study. A computer program was used to simulate water and solute behavior in the soil by using the finite element method. Although the code was found to be reliable, the accuracy in both water and salt content was not quantitatively satisfactory when compared with the measured values.