在泰国东北部的一个国家公园,农业土地已由小规模农民从天然林转变为木薯农业。我们假设长期的木薯单一栽培会导致土壤特性的退化。为了检验假设,我们进行了为期五年(2016-2020年)的木薯农田土壤理化性质研究,并检查了其邻近天然林的土壤特性,作为一个控制。在2011年至2015年的五年中,被检查的木薯农田由天然林转化。2016年发现有机碳的显着减少以及可交换钾和堆积密度的增加,这表明这些土壤特性在农田转换后迅速变化。另一方面,在2020年晚些时候发现了土壤氮素的显着增加和pH值的降低,这表明这些土壤特性因反复的农业活动而逐渐改变,如施肥和践踏。相比之下,有效磷酸盐没有显著差异,电导率,阳离子交换能力,和土壤质地(沙子的分数,淤泥,和粘土)在森林和农田土壤中。阳离子交换容量与粘土的分数呈正相关,有机碳,和pH。泰国国家公园内禁止使用草甘膦和百草枯除草剂。然而,2020年,在雨季和旱季,农田土壤中检测到草甘膦(高达5.0mgkg-1),至少在2020年的旱季,在农田的流水中检测到草甘膦(高达2.5mgl-1)。土壤退化和除草剂污染可能带来导致陆地生态系统不可逆转变化的高风险。我们从农业生产的角度讨论了这个问题的根源,经济,以及对环境的影响,并提出有效的政策措施。
In a national park in Northeast Thailand, agricultural land has been converted from natural forest by small-scale farmers for cassava agriculture. We hypothesise that long-termed cassava monoculture leads to the degradation of soil properties. To test the hypothesis, we conducted a five-year (2016-2020) study on the physical and chemical properties of soil in cassava farmland, and also examined the soil properties of its adjacent natural forests, as a control. The examined cassava farmland was converted from the natural forest during the five years from 2011 to 2015. The significant decrease in organic carbon and the increases in exchangeable potassium and bulk density were found in 2016, indicating that these soil properties varied quickly following the farmland conversion. On the other hand, the significant increase in soil nitrogen and the decrease in pH were found later in 2020, indicating that these soil properties were gradually altered by repeated agricultural activities, such as fertilizer application and trampling. In contrast, there were no significant differences in available phosphate, electrical conductivity, cation exchange capacity, and the soil texture (the fractions of sand, silt, and clay) among the forest and farmland soils. The cation exchange capacity was positively correlated to the fraction of clay, the organic carbon, and pH. The use of glyphosate and paraquat herbicides is prohibited within national parks in Thailand. However, in 2020, glyphosate was detected in farmland soil (up to 5.0 mg kg-1) during both the rainy and dry seasons, and glyphosate (up to 2.5 mg l-1) was detected in stream water from the farmland during the dry season at least in 2020. Soil degradation and herbicide pollution may carry a high risk of causing irreversible changes in terrestrial ecosystems. We discuss the root causes of this issue from perspectives of agricultural production, economy, and the environmental impact, and propose effective policy measures.