The Influence of Direct Green Waste Land Application on Greenhouse Gases Emission and Nitrate Leaching.

Global climate change has gained worldwide attention and efforts toward finding ways to mitigate greenhouse gas (GHG) emissions are called for. Recycling organic materials is of major importance for achieving the goal of GHG mitigation since organic materials comprise the largest waste category, accounting for 24% of the waste disposed in the United States. Two alternatives to disposing of greenwaste in landfills are composting and direct land application. Many studies have characterized the emissions of various GHGs from composting. However, there is a dearth of data quantifying the GHGs from direct land application of greenwaste, which includes surface disposal and incorporation of greenwaste into soil. To investigate the effects of these two approaches on GHG emissions and groundwater pollution potential, we conducted a field experiment in a fallow system in the Sacramento Valley, California, from 2013-14. Five treatments were applied in fall 2013: Control; Control + tillage; greenwaste disposal (6 inches height) on surface; greenwaste disposal (12 inches height) on surface; greenwaste (6 inches height) application followed by tillage. The result showed that methane (CH₄) was consumed at an average rate of 3.0 - 6.3 g carbon (C) ha^-1 d^-1 in all but the 12 inches height treatment. The surface disposal of greenwaste promoted carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions at average rates of 82-207 kg C ha^-1 d^-1 and 8.9-12 g N ha^-1d^-1, respectively. However, the total N₂O and CO₂emissions from the greenwaste application followed by tillage treatment were significantly lower than those in the greenwaste disposal (6 inches height) on surface treatment. Meanwhile, incorporated greenwaste into soil reduced nitrate leaching compared to the control + tillage treatment. These results indicate that to reduce the environmental impact of green waste disposal, green waste incorporation into soil is recommended. Further experiments over a longer period to investigate the potential of green waste application to GHG emissions and nitrate leaching, especially under different cover crop systems, would be useful to strengthen this assessment.