A wood based low-temperature biochar captures NH₃⁻N generated from ruminant urine-N, retaining its bioavailability

Abstract

Aims: Ammonia (NH₃) can be volatilised from the soil surface following the surface application of nitrogenous fertilisers or ruminant urine deposition. The volatilisation of NH₃ is of agronomic and environmental concern, since NH₃⁻N is a form of reactive nitrogen. Ammonia adsorption onto biochar has the potential to mitigate NH₃ losses, but to date no studies have examined the potential for reducing NH₃ losses when biochar is present in the soil matrix. Methods: We used ¹⁵N-enriched urine to examine the effect of incorporating a wood based low-temperature biochar into soil on NH₃ volatilisation. Then, we extracted the urine-treated biochar and compared its potential to act as a plant N source with fresh biochar, while growing ryegrass (Lolium perenne). Results: The NH₃ volatilisation from ¹⁵N-labelled ruminant urine, applied to soil, was reduced by 45% after incorporating either 15 or 30 t ha⁻¹ of biochar. When the urine-treated biochar particles were transferred into fresh soil, subsequent plant growth was not affected but the uptake of ¹⁵N in plant tissues increased, indicating that the adsorbed-N was plant available. Conclusions: Our results show that incorporating biochar into the soil can significantly decrease NH₃ volatilisation from ruminant urine and that the NH₃⁻N adsorbed onto the biochar is bioavailable. Further studies are now required to assess the temporal dynamics of the N pools involved.