Carbon dioxide and methane emissions from pasture soils and wetland soils, Kapuka dairy-farm, Watituna catchment

Abstract

Over the last century, increasing concentrations of atmospheric carbon dioxide and methane have caused global warming and climate change. Soil, a huge stock of carbon, plays an important role in driving the amount of atmospheric greenhouse gases because soil can absorb and release a considerable quantity of carbon. In New Zealand, agricultural soils account for a large proportion of greenhouse gas emissions. However, the actual magnitude of soil emissions is underestimated due to very limited soil-gas measurement protocols in place for the farming land. This lack of evidence-based data causes uncertainty on the estimates and the trending of greenhouse gas emissions in any given region. Importantly, it fails to effectively inform the future management decisions in adopting strategies to improve soils for reducing the emissions and turning soil carbon sources into carbon sinks. The study investigates the quantity of carbon dioxide (CO2) and methane (CH4) diffusing from pasture soils and wetland soils in a dairyfarm, Kapuka, Waituna catchment. It also assesses the spatial variability of the emissions associated with changes in soil moisture and temperature. Based on results, farm management guidelines have been recommended. The chamber technique and West System portable flux meter were used in the measurements. The monitoring was carried out on the plot of 105 measuring points. At each point, the chamber was placed on the ground surface for the gases diffusing into the instrument and being detected by the sensors. Soil moisture and air parameters were also measured and recorded. The data collected was then processed, analysed, and mapped by using ArcGIS tool. The results show the site is source of CO2 and CH4 emissions. The CO2 flux emits at the average of 17.5 g/m2/day, and the CH4 flux at 0.04 g/m2/day. Compared to the global rate, the study site emits a 120% higher increase in nominal flux. The wetland is a significant source of CO2 and CH4 with very high spatial variability. The highest CH4 flux was recorded at 5.1g/m2/day. Soil moisture, excess nutrients, and shallow water table are the driving factors for the emissions. It is recommended that farm management should focus on improving poorly drained soils, increasing soil organic matter content, and considering riparian planting to reduce nutrient runoff. Future research is recommended to assess the temporal variation of gas emissions and to particularly monitor nitrous oxide. Nitrous oxide is a major component of agriculture gas emissions that come from fertiliser application and manure deposit. Soil gas monitoring in wetlands and farming ‘hot spots’ within the region is also recommended