Pyrolysing poultry litter reduces N₂O and CO₂ fluxes

Abstract

Application of poultry litter (PL) to soil can lead to substantial nitrous oxide (N₂O) emissions due to the co-application of labile carbon (C) and nitrogen (N). Slow pyrolysis of PL to produce biochar may mitigate N₂O emissions from this source, whilst still providing agronomic benefits. In a corn crop on ferrosol with similarly matched available N inputs of ca. 116 kg N/ha, PL-biochar plus urea emitted significantly less N₂O (1.5 kg N₂O-N/ha) compared to raw PL at 4.9 kg N₂O-N/ha. Urea amendment without the PL-biochar emitted 1.2 kg N₂O-N/ha, and the PL-biochar alone emitted only 0.35 kg N₂O-N/ha. Both PL and PL-biochar resulted in similar corn yields and total N uptake which was significantly greater than for urea alone. Using stable isotope methodology, the majority (~80%) of N₂O emissions were shown to be from non-urea sources. Amendment with raw PL significantly increased C mineralisation and the quantity of permanganate oxidisable organic C. The low molar H/C (0.49) and O/C (0.16) ratios of the PL-biochar suggest its higher stability in soil than raw PL. The PL-biochar also had higher P and K fertiliser value than raw PL. This study suggests that PL-biochar is a valuable soil amendment with the potential to significantly reduce emissions of soil greenhouse gases compared to the raw product. Contrary to other studies, PL-biochar incorporated to 100 mm did not reduce N₂O emissions from surface applied urea,which suggests that further field evaluation of biochar impacts, and methods of application of both biochar and fertiliser, are needed.