Soil salinization under large-scale irrigation agriculture in Central Asia

为了分析土壤次生盐渍化的潜在风险，在哈萨克斯坦和乌兹别克斯坦不同地区进行了广泛的土壤调查，特别参考了土壤深层的盐浓度。在100 ~ 200 cm土层中，可溶性盐的含量有明显的区域趋势。1) Hi流域可溶性阳离子含量偏低。2)费尔干纳地区可溶性阳离子和SAR含量相对较低，叙尔河下游流域则有所增加。3)哈萨克斯坦北部土壤中可溶性阳离子含量较高，且Na含量较高。因此，深层土壤含盐量主要由地球化学因素决定。叙尔河下游流域和哈萨克斯坦北部发生次生盐碱化的基本风险高于Hi和费尔干纳盆地等冲积扇。分析了不同规模稻田土壤盐渍化的过程和风险，重点分析了地形和地下水位的影响。本研究考察了两个农场的土壤盐分、作物产量与当地地形等影响因素之间的关系。这两个农场的特点是坡度平缓，面积平坦，局部洼地。除位于洼地的水田外，大部分水田在灌溉期间均表现出冲盐现象。灌溉系统下部残留土壤盐分、深积水和排水能力不足对水稻产量产生不利影响。旱地的盐积累似乎随着种植年限的增加而增加，并且与灌溉系统下部地下水深度变浅有关，对大多数农田的作物生长产生不利影响。

To analyze the potential risk of secondary soil salinization, an extensive soil survey was conducted with special reference to salt concentration in deeper layers of soils in different regions of Kazakhstan and Uzbekistan. A clear regional trend was found in terms of contents of soluble salts in the 100-200 cm layers of soils. 1) In the Hi watershed, the contents of soluble cations tend to be low. 2) In the Fergana regions, the contents of soluble cations and SAR are relatively low, but are increased in the lower watershed of Syr-Darya River. 3) In northern Kazakhstan, soluble cations are usually high in subsoils with a high proportion of Na. Thus the salt contents in deep soil layers are primarily determined by geochemical factors. There is a higher fundamental risk for secondary salinization in the lower watershed of Syr-Darya River and northern Kazakhstan than in the alluvial fans such as the Hi and Fergana basins.Then process and risk of soil salinization in rice-based system was analyzed in respective farm scale, with special emphasis on the effect of topography and groundwater level. This study examined the relationships between soil salinity, crop yield and affecting factors including local terrain for two farms. Both farms are characterized by a gentle slope, flat area and localized depressions. Most of the paddy fields showed wash-out of salts during the irrigation period except in waterlogged fields situated in depressions. Rice yield was adversely affected by the remaining soil salinity, deep ponding water and insufficient drainage capacity in the lower part of the irrigation system. Salt accumulation in the upland fields appeared to increase with cropping years, and was associated with groundwater depth that became shallower at the lower parts of the irrigation systems, adversely affecting the crop growth in most fields.