Comparison of Organic Fertilizer Effects on Nitrous Oxide (N2O) and Carbon Dioxide (CO2) Emissions from a Lettuce Field.

Nitrogen (N) fertilizers support not only plant growth but also microbial activities such as decomposition, methanogenesis, nitrification and denitrification. Over application of N fertilizer may activate these microbial processes and cause the loss of carbon dioxide (CO₂) and nitrous oxide (N₂O) to the environment. Also, different types of fertilizers may cause different effects on the environment. Although there are many studies about the effect of synthetic fertilizers on greenhouse gas (GHG) emissions, there are only a few studies on organic fertilizers. The objective of this study is to evaluate the effect of four organic fertilizers: feather meal, blood meal, fish emulsion, and liquid cyanobacteria application at two application rates, 56 and 112 kg N/ha, on N₂O and CO₂ emissions from a lettuce crop. Both application rates of feather meal and 112 kg N/ha blood meal increased the total N₂O emission significantly as compared to the control (without fertilizer), and there was significant difference between 56 and 112 kg N/ha blood meal treatments in the total N₂O emission, 0.50 and 1.23 kg N/ha/season respectively. All fertilizer treatments did not show a significant increase on the total CO₂ emission. The liquid fertilizers (fish emulsion and liquid cyanobacteria) did not increase total N₂O emission significantly compared to the control, probably due to their application in small doses throughout the growing season as compared to the pre-plant application of the feather meal and blood meal treatments. These results suggested that fertilizers induced N₂O emission factors and 56 kg N/ha liquid cyanobacteria application will provide the lowest total CO₂ and N₂O emissions as compared to other application.