Clarification of soil degradation mechanism in dryland and environmental restoration for sustainable agriculture development

为了提高旱地农业的可持续性，在分析土壤盐渍化现状和原因的基础上，提出了盐渍化土壤的管理和修复方法。1）墨西哥南下加利福尼亚地区，大部分灌溉水（地下水）和表层土壤盐渍化，局部地区盐渍化加剧。土壤盐渍化过程主要受两个因素的影响。一是灌溉水水质和水量对盐分添加量的影响，二是底土质地对盐分淋溶的影响。合理的灌溉管理，即“节水”灌溉管理，是解决土壤盐渍化问题、恢复水资源的关键。2）建立了一种简便的土壤盐渍化风险评价方法。SSR由与土壤盐渍化有关的各因子的分值之和决定。利用该程序不仅可以对盐渍化的状况进行评估，而且可以对盐渍化的原因进行评估。3）验证了洪水利用农业系统的高度可持续性。农业利用包括悬浮泥沙在内的旱地地表径流是一种非常有用的方法，因为这种方法具有以下优良效果：4）研究表明，地肤具有较强的耐盐性和耐缺水性，能够在高盐条件下保持良好的生长，是干旱地区盐害严重地区有希望的饲料作物。阐明了盐碱地植物修复的优良植物--草海蓬子（Salicornia herbacea）幼苗在高浓度NaCl溶液中伸长生长的机理。

To improve the sustainability of the dry land agriculture, appropriate management and rehabilitation methods of salt affected soils were developed based on the analysis of status and causes of soil salinization,1) In Baja California Sur, Mexico, most of irrigation water (underground water) and top soil were salinzed, and have been aggravated in some area. Soil salinization process was mainly explained by two factors. One was irrigation water quality and quantity that influenced salt addition and another was soil texture of subsoils that influenced salt leeching. Proper irrigation management, that is "water-saving", is the key method to solve soil salinization and to recover water resources.2) A convenient procedure to assess soil salinization risk (SSR) was developed. SSR was determined by the sum of the points of various factors that relate to soil salinization. By using the procedure, not only the state but also the cause of salinization was assessable.3) High sustainability of the flood use farming system was verified. Agricultural utilization of surface runoff including suspended sediment in dryland was an extremely useful method, because this method had the following excellent effect ; storage of water, soil fertility improvement by deposition of suspended sediment and salt leeching in saline soil.4) It was clarified that Kochia scoparia, which had strong tolerance for salinity and water shortage, was able to maintain good growth under highly saline condition and would be a promising forage crop in dry region where the salt damage progressed. The mechanism of elongation growth of seedling of Salicornia herbacea that was a promising plant for phytoremediation of salinaized land was clarified under high concentration NaC1 solution.5) Combination use of a plant residue and sulfur might effectively improve sodicity level of soils by enhancing solubility of calcium.