Effects of slow and fast pyrolysis biochar on N₂O emissions and water availability of two soils with high water-filled pore space

Biochars, depending on the types of feedstocks and technological conditions of pyrolysis, can vary significantly in their properties and, therefore, it is difficult to predict biochar-induced effects on nitrous oxide (N₂O) emissions from various soils, their physical properties and water availability. The objectives of this study were (1) to quantify effects of slow pyrolysis biochar (BC) and fast pyrolysis biochar (PYRO) on physical and hydro-physical properties of sandy soil (Haplic Arenosol) and clayey loam soil (Gleyic Fluvisol), and (2) to assess corresponding N₂O emissions from these two soils. The study included a 63-day long laboratory investigation. Two doses of BC or PYRO (15 t ha⁻¹ and 30 t ha⁻¹) were applied to the soils in combination or without nitrogen fertilizer (NH₄NO₃, 90 kg N ha⁻¹). The obtained results have shown a significant decrease in the bulk density of sandy soil after it was amended with either rate of BC or PYRO. Water retention capacity of the soils in all the treatments with BC or PYRO increased considerably although no changes was found in the soil water-filled pore space (WFPS) which was higher than 60%. BC was increasing N₂O emission rates from the sandy soil treated with N fertilizer, and reducing N₂O emission rates from the clayey loam soil treated with N fertilizer. PYRO was more efficient and was reducing N₂O emissions from both fertilized soils, but for the sandy soil the reduction was statistically significant only at higher dose (30 t ha⁻¹) of the biochar.