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，在分析土壤盐碱化现状和原因的基础上，提出了相应的盐渍化土壤管理和修复方法：1)在墨西哥南巴哈加利福尼亚，大部分灌溉水(地下水)和表层土壤盐碱化，部分地区盐碱化加剧；土壤盐渍化过程主要由两个因素解释。一个是灌溉水质和水量对盐分添加的影响，另一个是下层土壤质地对盐渍的影响。合理的灌溉管理，即“节水”，是解决土壤盐碱化和恢复水资源的关键。2)建立了一种简便的土壤盐渍化风险评价方法。SSR由与土壤盐渍化相关的各种因素的点数之和决定。通过该程序，不仅可以评估盐碱化的状态，而且可以评估盐碱化的原因。3)验证了洪水利用农业系统的高度可持续性。旱地地表径流包括悬沙的农业利用是一种非常有用的方法，因为这种方法具有良好的蓄水效果，通过沉积悬浮泥沙和盐渍土壤中的盐渍来提高土壤肥力。4)阐明了耐盐碱和缺水的地黄能够在高盐分条件下保持良好的生长，在盐害严重的干旱地区是一种很有前途的牧草作物。阐明了盐角草幼苗在高浓度NaC_1溶液中的伸长生长机理。5)植物残体与硫磺配合使用，可通过提高钙的溶解度，有效地改善土壤碱化程度。

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.