福建省漳州市水稻物候特征对稻田土壤有机碳制图的影响

高精度土壤有机碳制图是研究耕地土壤有机碳时空格局及其影响机制的基础，相关研究结果可为农田“固碳减排”措施的制定提供决策支持。农业管理活动是农田土壤有机碳发生变化的重要影响因子，但基于农业管理活动的土壤有机碳制图却较为少见。基于遥感影像提取的物候参数是农业管理活动的直接反映，在研究农业管理活动对农田土壤有机碳的影响方面有较大应用潜力。基于此，本研究以福建省漳州市水稻田为研究对象，利用随机森林算法，基于5组不同的变量组合（A组：仅自然环境变量；B组：自然环境变量+早稻物候参数：C组：自然环境变量+晚稻物候参数；D组：自然环境变量+早稻物候参数+晚稻物候参数；E组：仅早稻物候参数+晚稻物候参数），分别构建土壤有机碳含量预测模型。通过对比5组模型的预测精度、预测值的空间分布特征和相关影响因子的重要性，分析物候参数对于土壤有机碳制图精度的影响作用，挖掘漳州市水田土壤有机碳制图的主要影响因子，解析对漳州市水田土壤有机碳有重要影响作用的农业管理活动。研究结果表明：物候参数的加入能够降低预测模型的误差和提升模型解释方差的能力；对漳州市水田土壤有机碳影响作用最大的物候参数依次为早稻季的NDVI增长速率（h1）、早稻生长季节开始的时间（a1）与早稻季NDVI下降速率（i1）；三个最重要的物候参数与土壤有机碳含量分别呈正相关、负相关和负相关，因此，采取能够促使早稻苗早生快发、加快早稻分蘖速率和减缓早稻衰老速率的水肥管理措施可增加耕地土壤有机碳含量。基于物候参数构建预测模型能有效提高农田土壤有机碳制图精度，基于物候参数的农田土壤有机碳制图研究可为农田管理提供决策支持，此次研究结果可为相关研究提供理论依据。     

Sheltering effect of punched steel plate sand fences for controlling blown sand hazards along the Golmud-Korla Railway: Field observation and numerical simulation studies

Sand fences made of punched steel plate (PSP) have recently been applied to control wind-blown sand in desertified and Gobi areas due to their strong wind resistance and convenient in situ construction. However, few studies have assessed the protective effect of PSP sand fences, especially through field observations. This study analyzes the effects of double-row PSP sand fences on wind and sand resistance using field observations and a computational fluid dynamics (CFD) numerical simulation. The results of field observations showed that the average windproof efficiencies of the first-row and second-row sand fences were 79.8% and 70.8%, respectively. Moreover, the average windproof efficiencies of the numerical simulation behind the first-row and second-row sand fences were 89.8% and 81.1%, respectively. The sand-resistance efficiency of the double-row PSP sand fences was 65.4%. Sand deposition occurred close to the first-row sand fence; however, there was relatively little sand on the leeward side of the second-row sand fence. The length of sand accumulation near PSP sand fences obtained by numerical simulation was basically consistent with that through field observations, indicating that field observations combined with numerical simulation can provide insight into the complex wind-blown sand field over PSP sand fences. This study indicates that the protection efficiency of the double-row PSP sand fences is sufficient for effective control of sand hazards associated with extremely strong wind in the Gobi areas. The output of this work is expected to improve the future application of PSP sand fences.