A comparative greenhouse gas emissions study of legume and non-legume crops grown using organic and conventional fertilizers

Abstract The cultivation of legume crops has been proposed as a way of reducing greenhouse gas (GHG) emissions because of their ability to fix atmospheric N and thus reduce the need for external N fertilizers. Moreover, the establishment of organic agriculture has been proposed as a sustainable strategy to enhance the delivery of ecosystem services, although crop yields are normally lower compared to conventional agriculture. The main objective of this study was to assess the effect of a legume and non-legume crop (fava bean and broccoli) during two years on crop yield, GHG emissions (N2O, CO2 and CH4) and soil enzyme activities, using conventional or organic fertilizers. GHG emissions, crop yield and enzyme activities differed between years. Fava bean generated the highest N2O and CH4 emissions, with no differences on CO2. Broccoli showed higher β-glucosidase and arylesterase activities. The use of conventional fertilizers resulted in higher crop yields for broccoli crop. The use of organic fertilizers led to higher N2O and CO2 emissions and soil enzyme activities in both crops, likely due to an increase of soil organic matter mineralization. Crop yield was related to lower GHG emissions and higher enzyme activities. Thus, legume crops may not reduce soil GHG emissions in all situations, and a thorough assessment should be carried out for each crop and pedoclimatic characteristics. This may be related to the ability of legumes to increase N availability through biological N fixation.