Coffee intercropping reduces soil N₂O and N₂ emissions: Empirical test and meta-analysis

Area of Science:

• Soil Science
• Environmental Science
• Agricultural Science

Background:

• Global coffee cultivation expansion necessitates understanding soil gaseous nitrogen losses in tropical regions.
• Coffee plantations enhance nitrogen mineralization, leading to nitrification and denitrification, producing nitrous oxide (N2O) and nitrogen (N2).
• The impact of coffee monoculture (CM) versus coffee intercropping (CI) on N2O and N2 emissions remains understudied.

Purpose of the Study:

• To investigate the effects of coffee plantations (CM and CI) and stand age on soil N2O and N2 emissions.
• To compare N2O and N2 emissions across natural forests, CM, and CI under varying oxygen conditions.
• To analyze microbial factors influencing denitrification and validate findings with a meta-analysis.

Main Methods:

• Field study comparing N2O and N2 emissions from natural forests, CM, and CI with different stand ages.
• Analysis of soil microbial communities, focusing on denitrification genes (nirK, nosZ-I).
• Meta-analysis to quantify the effects of coffee land use change (LUC) and fertilizer on N2O emissions.

Main Results:

• Coffee intercropping (CI) significantly decreased N2O and N2 emissions by 11-57% and 25-56.1%, respectively, compared to coffee monoculture (CM).
• Low-oxygen conditions amplified N2O and N2 emissions; CM and CI plantations showed 4.23-4.62 and 1.27-4.28 times higher cumulative N2O emissions than natural forests.
• Older coffee stands (34 years) exhibited significantly higher cumulative N2O emissions than younger stands (25 years).

Conclusions:

• Conversion of forests to coffee plantations substantially increases soil N2O and N2 emissions.
• Introduction of shade tree intercropping in coffee systems effectively alleviates soil N2O emissions.
• Coffee plantations promote microbial denitrification, contributing to increased gaseous nitrogen losses.