咸淡水轮灌对棉花产量和土壤溶质迁移的影响

Effects of alternative irrigation with brackish and fresh water on cotton yields and solute transport in soil

为探讨不同咸淡水膜下滴灌方式对棉花根系、产量和土壤剖面溶质迁移的影响,于2012–2013年在巴州灌溉试验站开展大田试验,共设置全生育期微咸水、淡水和咸淡水轮灌（蕾期—花铃前期淡水、其余生育期微咸水）3个处理。对比不同咸淡水处理下,棉花根系发育、地上部生长和产量的差异,分析0-100 cm土壤中铜、铁、锰、钙、钾、钠6种溶质垂向分布与变化特点。结果表明：2012年,微咸水灌溉条件下,钠离子未发生表聚,40 cm以上土壤微量元素含量显著增高（P〈0.05）,棉花总根长密度、最大根长密度呈咸水处理〉轮灌处理〉淡水处理,咸水和轮灌处理下,单株棉花地上部干物质、单位面积铃数和籽棉产量显著高于淡水处理,分别达32%、20%和22%。2012–2013年,咸水处理下棉花总根长密度骤减,导致该处理下单株棉花地上部干物质、单位面积铃数和籽棉产量显著降低（P〈0.05）。在土壤盐害离子增加,微量元素减少的情况下,采用蕾期至花铃前期淡水灌溉、其余生育期微咸水灌溉的方式,钠离子未发生表聚,2013年棉花总根长密度高于咸水处理达24%,地上部干物质、单位面积铃数和籽棉产量较咸水处理高出13%-24%。咸淡水轮灌一定程度上促进了棉花根系生长,缓解盐害离子对棉花造成的生长胁迫。另外,不同咸淡水灌溉处理下,土壤溶质迁移规律不同：2012–2013年,土壤中铜、铁、锰平均质量分数降低约40%,0-10 cm的表聚系数由0.14-0.17增长至超过0.20,3种处理下铜、铁、锰都表现出强烈的表聚性;钙、钾、钠平均质量分数增加33%-45%,3种处理下钙、钾未表现出明显的表聚性,而微咸水处理下钠由不表聚转变为显著表聚。该成果可为干旱地区合理利用微咸水,实现棉花优质稳产提供参考。

In arid or semi-arid areas, brackish water is often used for irrigation because of water shortage and soil nutrient deficiency. However, irrational irrigation with brackish water may lead to the accumulation of saline ions such as sodium, which might inhibit plant growth or even crop failure. In this study, we investigated the relationship between different irrigation methods and crop growth and yield in order to find a proper method of irrigation and fertilization. In order to achieve this objective, 2 years of field experiments in 2012 and 2013 were conducted at the experimental station in Korla, Xinjiang, China. Three irrigation treatments with brackish water, fresh water and alternative irrigation（20% of fresh water at bud and early boll stages, 80% of brackish water at late boll and boll opening stages） in the whole growing season were designed. Cotton and soil samples（from 0-100 cm depth） were collected in 4 days after the last irrigation. Cotton root were sampled with square monolith method in the space of 70cm×20cm×50cm. Root length density was estimated with DT-SCAN software. Available content of copper, iron, magnesium, calcium, potassium, and sodium in soil samples were extracted with Mehlich 3 reagent. Element content of cotton bolls were extracted after wet acid digestion（HNO3-HClO 4-HF）. Then, they were determined in triplicate by inductively coupled plasma optical emission spectrometer（ICP-OES）. Accumulation coefficient was defined as the ratio of nutrient content in soil layers of 0-10 cm or 0-20 cm to that in 0-100 cm, representing the element aggregation capability in topsoil. The results showed that when sodium did not accumulate in 2012, irrigation with brackish water significantly enlarge（compared to results in fresh water） the aboveground dry matter, numbers of bolls per unit area, and seed cotton yields by 32%, 20%, and 22%, respectively. Nevertheless, continuous irrigation using brackish water under heavy application of nitrogen fertilizer resulted in the surface aggregation of sodium, which significantly inhibited the root growth as well as aboveground dry matter and the yields. From 2012 to 2013, the total root length density decreased significantly under the brackish water treatment, which led to a sharp reduction of the aboveground dry matter, the numbers of bolls per unit area, and the seed cotton yields（P〈0.05）. In this case, the root length density, the aboveground dry matter, the numbers of bolls per unit area, and the seed cotton yields were improved by 12%-24% compared to the results for the brackish water treatment under the alternative irrigation. Moreover, the alternative irrigation did not essentially solve the problem of nutrient deficiency under the traditional cultivation pattern, thus a sustainable scheme of irrigation and fertilization should be made according to the solute variation in the soil. The average copper, iron, and magnesium in the soil profile reduced by 40% from 2012-2013 and the accumulation coefficients varied from 0.14-0.17 to over 0.20; however, the average calcium, potassium, and sodium increased by 33%-45% in the soil profile. For all treatments, calcium and potassium did not gather in the topsoil, whereas sodium under the brackish water treatment changed from weak to strong aggregation in the surface. This result provides valuble information for the rational irrigation and fertilization with brackish water in cotton cultivation.