生物炭料源-供應及應用管理平台

期刊

Effect of freeze-thaw cycling on grain size of biochar

Zuolin Liu, Brandon Dugan, Caroline A. Masiello, Leila M. Wahab, Helge M. Gonnermann, Jeffrey A. Nittrouer

PLOS ONE

13(1): e0191246

PLOS

2018/1/12

Biochar may improve soil hydrology by altering soil porosity, density, hydraulic conductivity, and water-holding capacity. These properties are associated with the grain size distributions of both soil and biochar, and therefore may change as biochar weathers. Here we report how freeze-thaw (F-T) cycling impacts the grain size of pine, mesquite, miscanthus, and sewage waste biochars under two drainage conditions: undrained (all biochars) and a gravity-drained experiment (mesquite biochar only). In the undrained experiment plant biochars showed a decrease in median grain size and a change in grain-size distribution consistent with the flaking off of thin layers from the biochar surface. Biochar grain size distribution changed from unimodal to bimodal, with lower peaks and wider distributions. For plant biochars the median grain size decreased by up to 45.8% and the grain aspect ratio increased by up to 22.4% after 20 F-T cycles. F-T cycling did not change the grain size or aspect ratio of sewage waste biochar. We also observed changes in the skeletal density of biochars (maximum increase of 1.3%), envelope density (maximum decrease of 12.2%), and intraporosity (porosity inside particles, maximum increase of 3.2%). In the drained experiment, mesquite biochar exhibited a decrease of median grain size (up to 4.2%) and no change of aspect ratio after 10 F-T cycles. We also document a positive relationship between grain size decrease and initial water content, suggesting that, biochar properties that increase water content, like high intraporosity and pore connectivity large intrapores, and hydrophilicity, combined with undrained conditions and frequent F-T cycles may increase biochar breakdown. The observed changes in biochar particle size and shape can be expected to alter hydrologic properties, and thus may impact both plant growth and the hydrologic cycle.

生物炭通過改變土壤的孔隙度、密度、透水性和保水力來改善土壤及地表水文狀態。這些性質與土壤和生物炭的粒徑分佈有關，並隨著生物炭風化而改變。此篇文章我們研究凍融循環如何在兩種排水情況下，影響松樹、豆科灌木、芒草和廢汙泥生物炭的粒徑：一種情形是(所有生物炭)在不排水情況下，另一種情形是(所有豆科灌木生物炭)在重力排水情況下。在不排水情況下的植物中，生物炭顯示出中質粒徑減少和粒徑分佈改變，這與生物炭表面薄層的剝落一致。生物炭的粒徑分佈從單峰轉變為雙峰，具有較低的峰和較寬的分佈。對於植物生物炭，在20個凍融循環後，中質粒徑尺寸減小最多45.8％，而粒徑長寬比增加最多22.4％。凍融循環不會改變廢汙泥生物炭的粒度或長寬比。我們還觀察到生物炭的骨架密度（最多增加1.3％），殼層密度（最多減少12.2％）和內部孔隙度（顆粒內部的孔隙，最多增加3.2％）的改變。在排水情況下的植物中，豆科灌木生物炭在10個凍融循環後顯示出中質粒徑尺寸減小（最多4.2％），長寬比並沒有改變。我們還記錄了粒徑減小與初始含水率之間的正向關係，這表明增加含水量的生物炭特性（例如高孔隙率和大孔隙內的孔連通性和親水性），以及不排水的情況下和頻繁的凍融循環可能會增加生物炭的分解率。預期觀察到的生物炭顆粒大小和形狀的變化會改變水文特性，也因此可能會影響植物的生長和水文循環。

biochar, grain size, freeze-thaw cycling, skeletal density, envelope density

https://doi.org/10.1371/journal.pone.0191246