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

Abstract

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 CO2 , N2 O and CH4 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 CO2 and N2 O but net sinks of CH4 . Carbon dioxide fluxes ranged from 4.38 to 14.49 mg CO2 -C m−2 hr−1 while those for N2 O were between 0.007 and 0.012 mg N2 O-N m−2 hr−1. Wetting soils receiving effluent enhanced CO2 production by 161%, suppressed N2 O fluxes by 17% but increased CH4 uptake by 286%. When compared with control locations, effluentonly locations observed 50% less CO2 , yet highest N2 O emissions were observed on the same locations. Nitrous oxide emissions were positively correlated with CO2 but negatively correlated with CH4 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.