Carbon dioxide, nitrous oxide and methane emissions from the Waimate District (New Zealand) pasture soils as influenced by irrigation, effluent dispersal and earthworms

Effects of wet/dry cycles in inducing greenhouse gas emissions are well documented. However, the effects of field drying and rewetting events remain poorly understood. This study investigated the impact of irrigation and effluent application on CO 2 , N 2 O and CH 4 in the Waimate District of New Zealand. Four soil management practices: (i) only added effluent, (ii) only added water, through irrigation, (iii) effluent and water added together, and (iv) neither water nor effluent added were sampled using static headspace chambers with a chamber diameter of 250 mm and height of 150 mm. All locations were sources of CO 2 and N 2 O but net sinks of CH 4 . Carbon dioxide fluxes ranged from 4.38 to 14.49 mg CO 2 -C m −2 hr −1 while those for N 2 O were between 0.007 and 0.012 mg N 2 O-N m −2 hr −1 . Wetting soils receiving effluent enhanced CO 2 production by 161%, suppressed N 2 O fluxes by 17% but increased CH 4 uptake by 286%. When compared with control locations, effluent-only locations observed 50% less CO 2 , yet highest N 2 O emissions were observed on the same locations. Nitrous oxide emissions were positively correlated with CO 2 but negatively correlated with CH 4 emissions. Irrigation-only locations had 33% more earthworms than effluent locations. Maximum density and biomass occurred where both effluent and irrigation were applied. There was no evidence of relationships between earthworm measurements and gas fluxes.