Intercropping with oilseeds enhances greenhouse gas mitigation during the initial establishment phase of tung trees

Abstract

The tung oil tree, Vernicia fordii (formerly Aleurites fordii), is used to produce biodiesel, and inter-row spacing during the cultivation of these trees allows other species to be grown alongside them, such as oilseeds. However, the sustainability of these intercropping systems in regard to greenhouse gas emissions and biodiesel oil production capacity is unknown. Hence, this study evaluated four intercropping systems during the initial establishment phase of tung trees over three growing seasons, namely: crambe (Crambe abyssinica)/sunflower (Helianthus annuus)/crambe with mineral fertilizer, crambe/sunflower/crambe with organic fertilizer; oat + vetch (Avena strigosa + Vicia sativa)/peanut (Arachis hypogaea L.)/oat + vetch without fertilizer, and fallow/fallow/fallow with the inter-rows left uncultivated. We measured methane (CH₄) and nitrous oxide (N₂O) emissions from the soil and estimated oil production, carbon (C) saving, and global warming potential (GWP) in each system. Peanut grain production surpasses that of sunflower and crambe, resulting in a higher oil yield when compared to non-legume oilseeds. Cumulative N₂O emissions were higher (p < 0.05) with intercropping compared to the fallow, varying from 0.18 to 1.42% with mineral fertilizer and 0.15–0.90% for organic fertilizer. However, there was no difference (p < 0.05) between the two N sources over the three growing seasons. Meanwhile, CH₄ oxidation in the soil was lower when organic fertilization was used. The intercropping system with cover crops in the winter and peanuts in the summer presented the greater C saving (4.81 Mg CO₂eq ha⁻¹) resulting in the more negative GWP (− 3.87 Mg CO₂eq ha⁻¹). This is the first study to evaluate the energy potential and C savings of different intercropping systems with tung oil trees. Our findings indicated that the sustainability of the production system can be increased when oilseed crops are intercropped with tung trees.