Sources of N 2 O–N following simulated animal treading of ungrazed pastures

A comparison of treading in the presence and absence of pre-grazing DM showed that reduced plant N uptake did not induce greater N 2 O emissions. Rather, the 15 N labelling of the NO 3 − –N pool indicated this pool contributed to the N 2 O emissions under treading. In addition, 15 N labelling showed other soil–N pools became available as a consequence of either, (1) treading inducing soil perturbation and releasing N from the soil organic matter–N and/or plant root–N pools, or (2) as a result of simulated grazing causing the release of plant root–N. Soil water soluble carbon (C) also increased under treading in the absence of pasture, supporting the theory that organic–N was released from either the soil organic matter (OM) or plant root pools.

Further research should investigate the effect of treading on the turnover and contribution of organic–N pools (roots, OM) in pasture soils in order to more fully understand the contributions these make to background N 2 O emissions and effects on N and C cycling in pasture soils.