Three‐dimensional pore structure and carbon distribution of macroaggregates in biochar‐amended soil

Abstract

Summary Incorporation of biochar improves the physical properties of soil that are needed for plant growth; in particular, it stabilizes soil's aggregate structure. There has been little research, however, on the effects of biochar on three‐dimensional (3‐D) soil structure and carbon distribution within aggregates. To investigate the effects we amended two soil types (Ultisol and Vertisol) with three types of biochar (at the rate of 40 g biochar kg−1 soil). We separated the macroaggregates (5–7 cm in diameter) into two sets to study the distributions of intra‐aggregate pores and carbon. Synchrotron‐based X‐ray micro‐computed tomography (SR‐mCT) indicated that application of woodchip biochar (WCB) and waste‐water sludge biochar (WSB) increased significantly the porosities of macroaggregates, whereas straw biochar (SB) was less effective. The increased porosity of macroaggregates in the biochar‐amended soil is attributed to both the original porosity in the biochar and newly formed pores resulting from the interaction between the soil and the biochar. The addition of straw biochar has no obvious effect on the spatial distribution of pores in macroaggregates of either soil, whereas WCB and WSB changed the directional pore distribution of the Vertisol macroaggregates considerably. In the WCB‐ and WSB‐amended Ultisol, the number of pores increased in the outer parts of the macroaggregates, thereby greatly improving the exchange of air, water and nutrients with the adjacent soil matrix. Carbon mapping of the macroaggregates showed that the application of SB did not greatly increase the carbon content of macroaggregates compared with the control. The addition of WSB to the Ultisol markedly increased the carbon concentration of macroaggregates. The heat‐map analysis indicated that the effects of biochar on pore structure and carbon content depend on the type of biochar and soil. The combination of SR‐mCT and scanning electron microscopy (SEM) has been shown to be powerful for quantifying the pore characteristics and carbon distribution in soil macroaggregates.

Phytotoxic Effects of Two Biochars Derived from Wood Chip and Sewage Sludge: Salt Stress and Toxic Compounds Tests

“…In other words, biochar application increased the water content by 8% and 2% for BC I and BC III respectively indicating that the most important value was observed for BC I. As found in the present study, the improvement of water retention capacities after biochar addition have previously been observed (Cao et al, 2014;Obia et al, 2016) and reported to be due to its porous nature (Yu et al, 2016 BC III had also a positive effect on water use efficiency (Fig. 4c).…”

Biochar additions can enhance soil structure and the physical stabilization of C in aggregates

“…This finding is in contrast to a more passive role that is more typically attributed to biochar where it contributes to soil C sequestration simply due to its recalcitrance. Much of the previous research on biochar has focused on increased soil C storage brought about directly from addition of biochar itself: many types of biochar are relatively stable (particularly those produced at high temperatures) and persistent in soil for extended periods of time (Mašek et al, 2013; Yu et al, 2016; Zimmerman, 2010). In contrast, our results suggest that biochar can play a more active role, by facilitating the physical protection of C (both biochar- and native-derived SOM) in aggregates, at least in the finer textured Yolo soil.…”

Biochar and Soil Physical Properties

“…The effect of biochar can be feedstock-specific. Using X-ray micro-computed tomography, Yu et al (2016) characterized the soil pore structure and reported that woodchip and wastewater sludge biochar increased the porosity of soil macroaggregates more than straw biochar.…”