Evaluation of agricultural resources and sustainability in tropical upland crop area developed in large scale

对泰国东北部和中部以及越南西北部在20世纪中期或之后发展为农业的农业生产系统的农业资源和可持续性进行了评估。主要成果如下。1)绘制了泰国东北部地区的长期气象资料，发现该地区气温和太阳辐射相对稳定，而降雨量不稳定，区域和年变化较大，且分布不均匀。此外，年降雨量与降雨日数之间不存在相关性，降雨日数的区域差异较大。甘蔗生产的最大限制因素是土壤含水量，而土壤含水量又与土壤粘粒含量有关。坡角对生产力影响不大。结果表明，泰国东北部地区普遍存在的沙质土壤有机质含量较低，肥效较低。2)在泰国中部蔬菜产区，广泛观察到一种独特的种植系统，即“戎颏”，这种种植系统使用凸起的床堤，大量施肥，表明在这种种植系统中，大量施用的肥料，特别是磷，没有被植物吸收，而是积累在周围环境中。在大田种植区，明确了根据环境条件建立多样化耕作和种植制度，在条件中等有利的地区，种植制度多样化指数最大。在这些地区，由于平缓起伏的地形和普遍较高的土壤粘土含量，土壤快速退化的可能性很低。3)在越南西北部的大田作物地区，有一点是明确的，即直到最近，传统上用于轮作种植的山坡被改为永久农田，生产经济作物，如玉米和食用美人蕉，采用适应其环境条件的多样化种植制度，尽管主要是耐侵蚀的粘土质肥沃土壤，但由于利用陡峭的山坡，土壤退化令人担忧。少

Agricultural resources and sustainability of agricultural producing systems in Northeast and Central Thailand, and Northwest Vietnam, which were developed for agriculture in the middle of 20th century or later, were evaluated. Major outcomes were as follows.1)Long-term meteorological data in Northeast Thailand were mapped, showing that in this area air temperature and solar radiation are relatively stable, whereas the rainfall is unstable with large regional and yearly variations, and uneven distribution. In addition, there was no correlation between annual rainfall and the number of rainy days and the number of rainy days showed large regional variations. Largest limiting factor for sugarcane production was suggested to be soil moisture contents, which in turn were related to be soil clay contents. The slope angle did not affect productivity pronouncedly. It is indicated that sandy soils prevailing in Northeast Thailand contains low organic materials and the efficiency of fertilizer a … More pplication was very low.2)In vegetable production areas in Central Thailand, unique cultivation system using raised-bed-dikes called "rong chin" with large amount of fertilizer application was broadly observed and it is suggested that in these systems large amount of applied fertilizers, especially phosphorus, was not absorbed by plants and accumulated in surrounding environments. In field crop areas, it is clarified that diversified farming and cropping systems have been established according to environmental conditions and diversification index of cropping system became largest in areas with moderately favorable conditions. In these areas, it is also suggested that the possibility for rapid soil degradation is low due to gently undulating topography and generally high soil clay contents.3)In field crop areas in Northwest Vietnam, it is clarified that mountain slopes, utilized traditionally for shifting cultivation until recently, were changed to be permanent crop fields, producing cash crops such as maize and edible cannas with diversified cropping systems adapted to their environmental conditions, and that soil degradation is worried because of the utilization of steep mountain slopes despite the predominance of erosion-resistant clayish fertile soils. Less