Biochar's effect on soil nitrous oxide emissions from a maize field with lime-adjusted pH treatment

Abstract

Biochar, a carbon-rich, porous pyrolysis product of organic residues may positively affect plant yield and can, owing to its inherent stability, promote soil carbon sequestration when amended to agricultural soils. Another possible effect of biochar is the reduction in emissions of nitrous oxide (N 2 O). A number of laboratory incubations have shown significantly reduced N 2 O emissions from soil when mixed with biochar. Emission measurements under field conditions however are more scarce and show weaker or no reductions, or even increases in N 2 O emissions. One of the hypothesized mechanisms for reduced N 2 O emissions from soil is owing to the increase in soil pH following the application of alkaline biochar. To test the effect of biochar on N 2 O emissions in a temperate maize system, we set up a field trial with a 20 t ha −1 biochar treatment, a limestone treatment adjusted to the same pH as the biochar treatment, and a control treatment without any addition. An automated static chamber system measured N 2 O emissions for each replicate plot ( n = 3) every 3.6 h over the course of 8 months. The field was conventionally fertilised at a rate of 160 kg-N ha −1 in 3 applications of 40, 80 and 40 kg-N ha −1. Cumulative N 2 O emissions were 53 % smaller in the biochar compared to the control treatment. However, the effect of the treatments overall was not statistically significant ( p = 0.26) because of the large variability in the dataset. Limed soils emitted similar mean cumulative amounts of N 2 O as the control. This indicates that the observed N 2 O reduction effect of biochar was not caused by a pH effect.