Spatial-temporal variations of nitrous oxide emissions in coffee agroforestry systems in Costa Rica.

This study investigates spatial-temporal trends in N 2 O emissions from coffee production systems in Costa Rica with a focus on the effects of nitrogen fertilisation, topography and soil type. This is done by combining (i) multi-year continuous dynamic chamber measurements from sites with different fertilisation levels, (ii) static chamber measurements taken along a typical sloping coffee field and (iii) measurements from a laboratory incubation experiment with nutrient addition to different soil types. In the field and in the laboratory, additions included standard NPK fertiliser, ammonium nitrate (NH 4 NO 3) as well as potassium nitrate (KNO 3). Soils in a laboratory experiment were incubated under both drained and flooded conditions. Continuous measurements from automatic chambers show that annual N 2 O fluxes were dominated by bursts over few weeks following N-fertilisation with peak emissions up to 60 g N-N 2 O ha−1 day−1. A two-month slope experiment with static chambers after KNO 3 -fertilisation with 90 kg N ha−1 showed N 2 O significant differences between the highest daily emission rates from the top and the bottom of the slope (134 ± 20 g N-N 2 O ha−1 and 336 ± 104 g N-N 2 O ha−1, respectively) which can be explained by NO 3 - transport downhill and flooded conditions favouring denitrification at the bottom of the slope. Incubation experiments indicate that denitrification is the main process controlling N 2 O emissions but also that nitrification can result in low N 2 O emission rates under drained conditions. It can be concluded that the reported N 2 O emissions from the coffee agroforestry systems are generally low, but may be underestimated, as both poorly drained depressions functioning as N 2 O hotspots as well as temporal N 2 O bursts need to be taken into account. • This study measures of N 2 O bursts from coffee production in Costa Rica. • N 2 O emissions are linked to fertilization and nitrate concentrations. • N 2 O budgets without including bursts underestimate the emission factor. • Local hydrology can result in hot spots of very high N 2 O emissions. • Contrasting soil types result in highly variable N 2 O emissions from coffee fields. [ABSTRACT FROM AUTHOR]