秸秆覆盖对地表能量平衡和土壤水分蒸发的影响机理

Straw mulching can regulate soil temperature by changing the surface energy balance and the process of water and heat transfer, so as to achieve farmland water storage and moisture conservation. As for the mechanism of straw mulching to regulate soil water and heat transfer, most studies are based on the energy balance between atmosphere and straw interface and the water and heat properties within soil, while ignoring the energy balance between soil and straw interface, resulting in a large deviation. In this project, the dynamic of soil surface heat flux, latent heat flux and sensible heat flux of soil-straw interface will be simulated, combined with the energy change characteristics of bare soil surface and air-straw interface under the same conditions, energy exchange between Atmosphere-Straw-Soil interfaces will be analyzed, to clarify the influence mechanism of straw mulching on the energy balance of soil-straw interface; Finally, integrating surface energy balance and soil sensible heat balance method, water evaporation above and within soil will be quantified using heat pulse technique, to reveal the process and mechanism of soil moisture evaporation under straw mulching. The results have important theoretical significance and application value for exploring the soil water-heat coupling mechanism under mulching conditions and establishing reasonable straw and soil water management measures.

秸秆覆盖通过改变地表能量平衡及水热运移过程，调节土壤温度，实现农田蓄水保墒。关于秸秆覆盖调节土壤水热过程的机理研究，大多数基于大气-秸秆界面的能量平衡和土壤中的水热状况，而忽略了土壤-秸秆界面的能量平衡，导致结果存在较大偏差。本项目拟通过土壤-秸秆界面地表热通量、潜热通量和感热通量动态变化规律的实验和模拟研究，结合相同条件下裸土表面和大气-秸秆界面的能量平衡特征，分析大气-秸秆-土壤两个界面间的能量交换规律，阐明秸秆覆盖对土壤-秸秆界面能量平衡的影响机理。在此基础上，融合地表能量平衡和土壤感热平衡原理，利用热脉冲技术对地表和土壤中水分蒸发进行定量化，揭示秸秆覆盖下土壤水分蒸发的过程及机制。研究结果对探讨覆盖条件下土壤水热耦合机理、建立合理的秸秆和土壤水分管理措施具有重要的理论意义及应用价值。

地表能量平衡是土壤-大气间进行能量和物质交换的纽带，秸秆覆盖可以改变地表能量平衡及水热运移过程，调节土壤温度，对农田蓄水保墒具有重要作用。为此基于野外试验，利用热脉冲技术和模型模拟，研究了秸秆覆盖对地表能量平衡和土壤水分蒸发的影响机理。研究结果表明：大气-秸秆界面和大气-土壤界面地表净辐射的变化范围分别为-0.20至2.53和-0.24至2.40 MJ m-2。大气-秸秆界面的净辐射大于大气-土壤界面的净辐射，随净辐射值的增大，两者的差异也有所增大；大气-秸秆界面和大气-土壤界面感热通量的变化范围分别为-0.28至1.26 MJ m-2和-0.13至1.10 MJ m-2，在含水量较大时，感热通量值较小，且两个界面感热通量的差异也较小，随时间推移，大气-秸秆界面的感热通量大于大气-土壤界面感热通量值，两个界面感热通量的差异变大；在界面含水量较大时，大气-秸秆界面的每日累积潜热通量大于大气-土壤界面和秸秆-土壤界面，随含水量降低，大气-土壤界面的潜热通量值逐渐大于其它两个界面；地表热通量变化规律与潜热通量较为相似。通过分析各界面地表能量平衡闭合度得出，大气-秸秆界面和大气-土壤界面地表能量闭合度平均值分别为93.37%和101.97%，闭合度较好。对比秸秆覆盖和无秸秆处理土壤水分蒸发，得出无秸秆的蒸发量明显大于有秸秆覆盖处理的蒸发量，最大差异达到0.61 mm。随着时间推移，土壤含水量降低，两个处理的蒸发量差异逐渐减小。在八天的测定期间，秸秆覆盖可减少蒸发量2.23 mm。由此可见，基于热脉冲技术和模型模拟计算得到的各通量值较为准确，能够达到较好的能量闭合度，7.5t hm-2的秸秆覆盖可以提升土壤保水效果。研究结果可以为地表能量平衡及农田秸秆管理提供一定的数据支持。