Effects of Biochar Addition on Thermal Properties of Loamy Soil
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the National Natural Science Foundation of China (Nos.41401241, 41471180),Natural Science Foundation of Jiangsu Province of China (No.BK20140724)

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    Abstract:

    【Objective】Soil thermal properties, including soil thermal capacity, conductivity, and diffusivity, play crucial roles in partitioning of surface-energy and heat transmission across the soil profile and consequently affect spatiotemporal dynamics of soil temperature that determines soil micrometeorology. As a soil amendment being able to improve a series of soil physiochemical properties, Biochar has gained wide attention. However, little information is available in the literature on integrated effects of biochar application on soil thermal properties. 【Method】A two-year field experiment using wheat straw derived biochar was conducted in a field of loamy soil in East China. The experiment was designed to have three treatments different in biochar application rate: 0 t hm-2 (BC0), 25 t hm-2 (BC25) and 50 t hm-2 (BC50) and three replicates for each. A total of 9 plots were arranged in a random complete block design. Tomato was grown under drip irrigation for two seasons. Soil thermal properties, i.e. thermal capacity, conductivity and diffusivity, were measured using the heat-pluse method in two ways: (1) lab-analysis of undisturbed soil cores collected from the plots with set soil water content; and (2) in-situ measurement under natural conditions. Besides, soil bulk densities, soil water retention curves, soil pore size distributions and soil water contents of the plots were also measured. 【Result】 In soils with controlled soil water content, soil thermal capacity increased with soil water content in the range from 1.13 J cm-3 K-1 to 2.80 J -3 K-1, from 1.16 J cm-3 K-1 to 2.75 J cm-3 K-1and from 1.07 J cm-3 K-1 to 2.74 J cm-3 K-1 in Treatmenta BC0, BC25 and BC50, respectively. Soil thermal capacity was significantly decreased by biochar application in the treatments moderate in soil water content (20%~30%), whereas the effects was insignificant in the treatments low (0~15%) or high (> 35%) in soil water content. Similarly, soil thermal conductivity increased with soil water content, in the range from 0.24 W m-1 K-1 to 1.16 W m-1 K-1, from 0.19 W m-1 K-1 to 1.09 W m-1 K-1 and from 0.18 W m-1 K-1 to 1.03 W m-1 K-1 in Treatment BC0, BC25 and BC50, respectively, and was significantly higher in the treatments amended with biochar, regardless of soil water content. Soil thermal diffusivity varied in the range from 0.23 m2 s-1 to 0.45 m2 s-1, from 0.16 m2 s-1 to 0.42 m2 s-1, and from 0.17 m2 s-1 to 0.41 m2 s-1 in Treatment BC0, BC25 and BC50, respectively. Soil thermal diffusivity was significantly lower in the treatments amended with biochar either low (0~15%) or high (>35%) in soil water content, while insignificant difference was detected in thermal diffusivity between treatments moderate in soil water content (20%~30%), but different in biochar application rate. Under field conditions, soil thermal capacity was significantly higher in Treatment BC50 than in Treatment BC0, but significantly lower in Treatment BC25 than in Treatment BC0. Biochar application had significant effects on soil thermal conductivity and diffusivity under field conditions. Treatments BC25 and BC50 were significantly lower in thermal conductivity and diffusivity than Treatment BC0 and lower in soil bulk density, too. However, soil total porosity was significantly increased by biochar application, which was mainly attributed to the increase in macropores (> 0.03 mm). Besides, biochar application also affected soil water retention curves in shape and soil water content was significantly higher in the treatments applied with biochar than Control during the growing seasons.【Conclusion】 Biochar application can significantly affect soil thermal properties through the two main mechanisms as follows: (1) biochar application promotes soil aggregation, thus forming large volumes of air filled pores; and (2) biochar application alters soil hydrological properties, thus increasing soil water content and hence soil thermal capacity and conductivity. In field conditions, the negative effects biochar application brings about on soil structure are much stranger than the positive ones it has on soil water content.

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LIU Zhipeng, XU Jienan, SHE Dongli, LI Xuelin, WANG Jingfan. Effects of Biochar Addition on Thermal Properties of Loamy Soil[J]. Acta Pedologica Sinica,2018,55(4):933-944.

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History
  • Received:August 25,2017
  • Revised:December 08,2017
  • Adopted:January 18,2018
  • Online: April 24,2018
  • Published: