Effects of organic and inorganic fertilizers on greenhouse gas (GHG) emissions in tropical forestry

Abstract

The production of organic wastes tends to increase in a manner that is proportional to human population growth. Currently, applying these wastes to soils is being considered as an alternative solution for the over production of organic waste. However, the levels of greenhouse gas (GHG) emissions from organic waste applications in tropical forestry are unknown. The aim of the present study was to quantify soil carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) emissions from a reforestation project, where trees (Calophyllum brasiliense) were fertilized with different mineral and organic waste materials. A randomized trial was established to measure soil GHG emissions from plots fertilized with sewage sludge compost (SSC), sewage sludge (SS), mineral fertilizer (Min Fert) and a control (C). C. brasiliense seedling spaced in 3m×2m intervals were place into a planting hole which had fertilizer incorporated for seedling establishment. Soil GHG were measured using the static chamber method, placing chambers on the surface of the soil and taking measurements over time, during 172days in a dry season. Organic wastes (SS and SSC treatments) had significantly higher soil CO2 fluxes than mineral fertilizer and control plots, with soil CO2 fluxes of 6.35±1.17 and 9.33±0.96gCm−2day−1, respectively. The application of organic wastes promoted a drastic increase in soil N2O emissions treated with SSC (141.19mg±21Nm−2day−1, p<0.01), which had a higher emission factor (2.11%). Average soil CH4 flux on collection days was −0.1±0.2mgCm−2day−1, although cumulative soil CH4 emissions over the 5months study period was positive for the SS treatment, demonstrating the potential emission of GHG from this treatment. Apparently, the variation in fluxes between treatments with organic residues was influenced by differences in the physical and chemical compositions of the wastes and the amounts of labile carbon added.