Water and salt behavior in the soil under micro irrigation

在温室内称重直径1.5米、土壤深度1.6米的渗水器，填满海岸沙，从1996年9月中旬开始，用合成盐水滴灌橘子树约1个月，从1997年8月中旬开始，用1个半月。用NaCl和CaCl_2两种化学药剂配制灌溉水，使其总浓度达到2000 mg/l （EC=4.0dS/m）。每天供水量相当于前一天蒸散量（ET）的1.2倍。自来水灌溉最大日蒸散量为4.2kg/d。在自来水灌溉条件下，日蒸散发与蒸发皿蒸发量有较强的相关性，相关系数为0.955。盐对ET的影响在盐水灌溉开始后立即发生。与自来水灌溉相比，2周内盐水灌溉条件下的ET降低了20-25%。试验结束时，橙树根部土壤盐分积累较高，ECe=3.5dS/m，距树10cm深度10 ~ 60cm处土壤盐分积累较低，为1.4 ~ 1.6 ds /m。当土壤ECe低于1.7dS/m时，橙子产量下降为零，当土壤ECe=3.3dS/m时，橙子产量下降为25%。该研究表明，对ET的影响比生产更严重和不利。利用计算机程序，采用有限元法模拟了土壤中的水分和溶质行为。虽然发现该规范是可靠的，但与测量值相比，水和盐含量的准确性在数量上并不令人满意。

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.