南疆膜下滴灌棉田节水控盐高效排灌指标研究

Oasis area of South Xinjiang is typical soil salinization development area. Drip irrigation under mulch technique has gained remarkable economic and social benefit, but the problem of salt accumulation in unsaturated root zone is existed, and with the increase of durable years, secondary salinization of soil becomes aggravated gradually. The salinized soil of cotton field in South Xinjiang was taken as research object. While ensure the effect of water saving and salinity control, the pipe drainage technique is applied, and the pot experiment, field experiment and numerical simulation was combined to analyze the influencing mechanism of water and salt stress to cotton growth and yield in root zone during different growth stage. On these basis, the salt-tolerant threshold value is defined; The response process of salt leaching in farmland to different irrigation quota during non-fertile stage is mainly focused, as well as the adjusting mechanism of irrigation quota to water and salt movement and changing progress in cotton root zone during different growth stage; Spatial distribution characteristics of water and salt in mulched cotton root zone soil under different irrigation and drainage condition; The irrigation and drainage indexes (leaching amount during non-fertile stage, irrigation quota during growth stage, buried depth of subsurface drainage pipe and spacing between subsurface drainage pipe)that suitable for Oasis area of South Xinjiang will be put forward, and it is hope that scientific basis will be provided to improvement of saline land in Oasis area of South Xinjiang

南疆绿洲区是我国土壤盐渍化发育的典型地区。膜下滴灌技术的推广取得了显著的经济效益和社会效益，但存在着非饱和根区积盐问题，随着其使用年限的增加，土壤次生盐碱化问题逐渐加重。因此，本项目以南疆典型盐渍土棉田为研究对象，在保证膜下滴灌节水增效控盐作用的前提下，应用暗管排水技术，采取筒栽试验、田间试验与数值模拟相结合，分析不同生育阶段棉花根区水盐胁迫对棉花生长及产量的影响机制，阐明棉花不同生育期的耐盐阈值；重点探讨非生育期农田盐分淋洗对不同灌水定额的响应过程以及生育期内不同灌水定额对棉花根区水盐运动及消长过程的调控机理；探明不同灌排条件下膜下根区土壤水盐空间分布特征；提出适于南疆绿洲盐碱地的排灌指标（非生育期淋洗量、生育期灌溉定额、暗管埋深、暗管间距），以期为南疆绿洲灌区盐碱地改良提供科学依据。

本项目以南疆典型盐渍土棉田为研究对象，以节水、增产和高效协同发展为目标，结合室内土柱模拟实验、田间定位实验和数值模拟分析，探明暗管排水技术参数对土壤盐分淋洗的影响；揭示暗管排水条件下膜下滴灌棉田土壤水盐分布特征及其对棉花生长的影响，提出适合于南疆盐碱地的排灌指标，得到主要结论如下：. （1）在灌水量一定的情况下，渗流速度和盐分置换量均随着水盐置换区的增大而减小；而在同等水盐置换区条件下，渗流速度和盐分置换量均随着灌水量的增加而增大；当暗管埋深为140和160cm，灌水量分别大于212和266m3/亩时，暗管排盐量均大于微咸水（2─5g/L）带入暗管水盐置换区的盐分，土壤含盐量（0─60cm）均达到棉花耐盐临界值，可同时满足棉花生长和土壤盐分淋洗要求。该结果可为科学制定微咸水灌溉制度提供理论依据。. （2）暗管排水技术参数对土壤盐分均具有不同程度的淋洗效果，且脱盐效果随着暗管间距的增加而降低，生育期末棉田由年内积盐转变为脱盐，而未铺设暗管处理生育期灌水后土壤会发生返盐现象；暗管排水处理棉花出苗率、棉花株高、叶面积和产量等生长指标均随暗管排水间距的减小而升高；暗管排水并未改变土壤微生物群落结构的稳定性，暗管排水处理组和对照组之间的微生物多样性无显著差异，冗余度分析（RDA）表明，土壤盐分和硝酸盐是苗期和花铃期土壤细菌和真菌群落变化的主要驱动因子。. （3）随着土壤湿润区由窄深型向宽浅型过渡，膜下土壤带状湿润均匀性越好，行间棉花根系分布和植株生长也愈加均匀、产量及水分利用效率也越高。窄深型土壤湿润区的膜下内、边行棉花根长密度、根系吸水能力和实际总产差值分别为386.3m/m3、0.39cm2和509.3kg/hm2，其水分利用效率分别为7.2和14.8kg/(mm•hm2)。宽浅型土壤湿润区的膜下内、边行棉花根长密度、籽棉理论总产和实际总产差值分别为142.01m/m3、0.10cm2和190.6kg/hm2，其水分利用效率分别为9.2和11.0kg/(mm•hm2 )。表明在膜下滴灌技术设计中应关注膜下土壤带状湿润均匀性指标。