Structural and chemical changes in pyrogenic organic matter aged in a boreal forest soil

Pyrogenic organic matter(PyOM)is formed during wildfires and prescribed burnings or produced intentionally in the form of biochar for soil amendment purposes.It is attracting a growing scientific and practical interest due to its important role in the global carbon cycle and agronomic applications as a soil enhancer.Most of the studies on the physicochemical properties of PyOM have been conducted using fresh biochars even though the characteristics of PyOM are expected to alter due to aging processes in soil environment.In this paper,we report the results of a study that utilized X-ray microtomography and elemental analysis to investigate the chemical and structural changes in the PyOM formed during prescribed burning events and aged thereafter for 1–71 years in a boreal forest soil.Our results indicate that changes in elemental composition occurred at decadal timescales,and an apparent steady state was reached ca.30 years after PyOM formation and exposure to the environment.At such timescales,PyOM was able to retain its porous structure originating from the cellular structure of the initial wood tissues.However,structural analysis revealed several effects of aging on the pore structure,such as the formation of surface coating layers,pore fillings,and fractures.These changes may alter pore size distribution and accessibility of the pores and further alter the influence of PyOM on soil functions,such as the transfer and retention of water and nutrients in PyOM pores.

Fertilizer and soil conditioner value of broiler manure biochars

Pyrolysis is an option for enhancing the sustainable management of broiler manure surpluses by producing a concentrated,hygienic char product with a fertilizer and soil conditioner value.In this study,the impacts of pyrolysis conducted at 350,400 and 450℃ on total nutrient and harmful element concentrations in biochars derived from peat-bedded broiler manure were examined.Emphasis was placed on the availability of phosphorus(P).In addition,the pore structures of these biochars were explored using X-ray microtomography and image analysis.During pyrolysis,35-50%,40-55%and 35-45%of the original carbon,nitrogen and sulfur contents,respectively,of the feedstock biomass were lost as volatiles.Mineral elements,including P,were concentrated in the biochar.Although water-extractable P was found to be converted to less labile forms due to charring,the concentration effect and notable increase in sodium bicarbonate-extractable P rendered broiler manure biochars richer in total labile P in comparison with feedstock manure(7.1,10.0,11.1 and 14.8 g labile P kg^(−1)in feedstock and biochars produced at 350,400 and 450℃,respectively).The pore volume of the micrometer-scale porosity of the broiler manure biochar was comparable to that found earlier in wood-based biochars.In comparison with wood-based biochars,the pore structure of broiler manure biochars was more versatile,and the pore size distribution was wider.Consequently,part of the porosity was too large to store plant-available water,which may reduce the potential of broiler manure biochars to improve soil water storage capacity.