Water and salt behavior in the soil under micro irrigation

在绿色温室内，用直径1.5m、埋深1.6m的称重式蒸渗仪，用人工合成盐水对橙子进行滴灌，分别于1996年9月中旬和1997年8月中旬进行。用NaCl和CaCl_2两种化学物质配制灌溉水，使其总浓度为2, 000 mg/l（EC=4.0dS/m）。每天供水量为前一天蒸散量的1.2倍。自来水灌溉的最大日ET为4.2kg/d。在自来水灌溉的情况下，日蒸散量与蒸发皿蒸发量之间有很强的相关性，相关系数为0.955。盐对ET的影响发生在盐水冲洗开始后立即。与自来水灌溉相比，盐水灌溉条件下ET在两周内下降了20-25%。试验结束时，橙子树根部土壤盐分积累量最大，EC_e =3.5dS/m，距树10 cm处10- 60 cm土层的EC_e值较低，为1.4-1.6dS/m。当土壤EC e小于1.7dS/m时，橙子产量下降为零，当EC e =3.3dS/m时，产量下降为25%。本研究提示，对ET的影响比对生产的影响更为严重和不利。利用有限元法编制了一个计算机程序，模拟了土壤中水分和溶质的行为。虽然该代码被认为是可靠的，在水和盐含量的准确性是不满意的定量时，与测量值相比。

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.