内蒙古河套灌区灌排水离子组成及淋洗盐分用水量评价

Evaluation of irrigation and drainage water cation composition and salt leaching requirement in Hetao Irrigation District

以河套灌区"盐分去向"为研究背景,通过调查灌区土壤及各级灌排渠系水阳离子含量变化及室内模拟灌溉水淋洗土柱试验,分析灌溉水经过土壤到排水阳离子组成的变化规律,探讨用Na+浓度评价淋盐排灌水量比的可行性。结果表明,与灌溉水相比,各级排水干渠排水所含盐分中Na+所占比例明显增加,平均约为87%;Ca2+所占比例减少,平均约为7%。排水的全盐浓度(EC)和Na+浓度有显著相关关系,说明Na+浓度对排水的全盐浓度有显著影响。灌溉水的2/3 Ca2+以非水溶性钙盐积聚在土壤,排出量较少,但灌区全年的Na+收支基本平衡。淋盐排灌水量比评价分析结果表明,用Na+浓度评价淋盐排灌水量比要优于用全盐浓度(EC);要维持灌区Na+收支平衡,排灌水量比应保持在0.12～0.15,针对现有灌区年引水量50亿t,年排水量要达到6～7亿t。

To determine where the salts go,variations in cation compositions of soil,irrigation water and drainage water in Hetao Irrigation District were analyzed.Field investigations and simulations of soil column leaching experiments were conducted to determine the changes in cation concentrations in irrigation water,drainage water and in soil profile.The study also discussed the use of water soluble Na＋ concentration to determine irrigation/drainage ratio for salt leaching（LR）.The results showed that the average ratio of Na＋ to total salts in different drainage canal waters was about 87%,which was higher than that in irrigation water.The average ratio of Ca2＋ was about 7%,which was lower than that in irrigation water.A significant correlation was noted between EC and Na＋ concentration.This indicated that Na＋ significantly influenced total salt concentration in drainage water.There existed an annual balance in Na＋ input-output in irrigated areas.However,about 2/3 of irrigation water Ca2＋ accumulated in soils with less water insoluble cation discharge.LR determined via Na＋ proved to be better than using EC.Based on the results,a balanced Na＋ input-output required an LR of 0.12～0.15.It meant that an annual drainage of 0.6～0.7 billion tons was reasonable for the annual irrigation of 5 billion tons in Hetao Irrigation District.