Abstract
The use of biochar reduces nitrous oxide (N2O) emissions from soils under specific conditions yet the mechanisms through which interactions occur are not fully understood. The objectives of this glasshouse study were to investigate the effect of (i) biochar particle size, and (ii) the impact of soil inversion—through simulated mouldboard ploughing—on N2O emissions from soils to which cattle urine was applied. Pine biochar (550 °C) with two different particle sizes (<2 mm and >4 mm) was mixed either into the top soil layer at the original 0–10 cm depth in the soil column or at 10–20 cm depth by inverting the top soil to simulate ploughing. Nitrous oxide emissions were monitored for every two to three days, up to seven weeks during the summer trial and measurements were repeated during the autumn trial. We found that the use of large particle size biochar in the inverted soil had significant impact on increasing the cumulative N2O emissions in autumn trial, possibly through changes in the water hydraulic conductivity of the soil column and increased water retention at the boundary between soil layers. This study thus highlights the importance of the role of biochar particle size and the method of biochar placement on soil physical properties and the implications of these on N2O emissions.
Highlights
The primary sources of nitrous oxide (N2 O) emissions from New Zealand pastoral soils are excreta from grazing animals, followed by urea and farm dairy effluent applied to soils [1]
In the present soil column study, we investigated the effect of biochar particle size and the impact of soil inversion—through simulated mouldboard ploughing—on N2 O emissions from soils to which cattle urine was applied
While biochar addition had no effect on plant N, soil inversion caused an increase in N plant uptake in all summer treatments, the effect was only significant for the control (UC: 12.7 g N m−2 ; inverted control (IC): 13.4 g N m−2 : p = 0.018) (Table 3)
Summary
The primary sources of nitrous oxide (N2 O) emissions from New Zealand pastoral soils are excreta (urine and dung) from grazing animals, followed by urea and farm dairy effluent applied to soils [1]. In 2013, the New Zealand Government adopted the unconditional targets of reducing greenhouse gas (GHG). Nitrous oxide can be produced in soil via nitrification, denitrification and nitrifier-denitrification. The nitrification process involves the oxidation of ammonium (NH4 + ) into nitrite (NO2 − ) and this into nitrate (NO3 − ) producing N2 O as by-product, while the denitrification process involves the reduction of NO3 − into gaseous nitrogen (N) compounds, mainly N2 O and dinitrogen gas (N2 ). Emissions to 5% below the 1990 level by year 2020, followed by post-2020 commitments to reduce greenhouse gas emissions to 11 and 50% below the 1990 level by year 2030 and 2050 [3], respectively, which forces the need to develop economically and technically feasible options in order to achieve such goal.
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