砂田抑制蒸发功能随覆砂年限的演变规律

Service Life of the Gravel-sand Mulch in Reducing Soil Evaporation

【目的】研究压砂覆盖(砂田)保温及抑制蒸发功能随砂田退化程度的演变规律。【方法】基于多年Landsat卫星数据,使用辐射传输方程法反演香山地区砂田地表温度(LST),结合田间地表温度监测,对比砂田与裸地的地表温度变化,分析了砂田抑制土壤蒸发的机理,并探讨了砂田的功效与砂田使用年限的关系。【结果】砂田在LST-NDVI梯形空间中贴近于暖边,其土壤水分比耕地少,接近于干土层。因此,砂田可以隔离辐射与土壤表层,从而减小潜热通量,抑制土壤蒸发。砂田昼夜温差明显比裸地大,且对于西瓜等作物,砂田的有效地表积温也比裸地提高了10%。【结论】砂田退化过程可分为纯砾石阶段、砂土混合阶段和砂土连通阶段,从砂田的保温及抑制蒸发功能来看,砂田的有效使用年限为25～30 a。

【Objective】Gravel mulch is an effective method to reduce soil evaporation, but its service deteriorates as time elapses. In this paper we studied the change in capability of a gravel mulch in thermal preservation and evaporation inhibition using satellite imagery.【Method】The analysis was based on the Landsat satellite data, and the radiative transfer equation was used to inversely calculate the surface temperature(LST) of a gravel-sand mulched field in Xiangshan. Combining with the observed LST, we compared the change in surface temperature of the mulched and bare ground, from which we analyzed the efficacy of the mulch in reducing soil evaporation and its degradation as the mulch was aging.【Result】The mulch was close to the warm edge in the LST-NDVI trapezoidal space and the soil moisture in it was lower than that in the cultivated land;it is close to that in the dry soil.The gravel-sand mulch can attenuate the radiation to reach soil surface, thereby reducing the latent heat flux and consequently soil evaporation. The day-night temperature oscillation in the mulched field was more substantial than that in the bare field. We also found that for watermelon, mulching increased the effective surface cumulative temperature by 10% compared to the bare field.【Conclusions】Degradation of the gravel-sand mulch can be divided into pure gravel-sand stage, sand-soil stage and sand-soil connection stage. Based on our results, the effective serviceable life of the mulch is approximately 25~30 years.