Cover crops improve soil fertility and have contrasting effects on leaf and root maize litter decomposition in the Pampas, Argentina

Abstract

Planting cover crops has been proposed as a keystone to restore ecosystem services in intensively cultivated agroecosystems. Cover crops increase primary production over time, positively impacting carbon storage, soil fertility and soil organisms. This plant cover can also alter litter decomposition processes through changes in biotic and abiotic conditions. However, most studies on cover crops for carbon turnover have focused on their legacy effects as litter inputs (“afterlife effects”). In contrast, the effects of living (green) cover crops on crash crop litter decomposition have rarely been quantified. We explored the effect of two cover crops (oat and oat-vetch mixture) on maize litter decomposition (1) under real field conditions in the Argentine Pampas, specifically with leaf litter decomposing on the surface and root litter slightly buried. Additionally, we placed buried leaf litterbags to (2) assess the effect of tillage management on carbon turnover and (3) evaluate litter quality effects independent of position. Finally, we manipulated cover crop biomass to (4) examine the impact of reduced sunlight exposure on litter decomposition. Our results show that cover crops improved soil biological properties and affected leaf and root maize litter decomposition differently. Soil microbial biomass and nitrogen retention increased under cover crops. Maize leaf litter decomposition also increased, while root litter tended to decrease. In addition, leaf litter aboveground decomposed faster than root litter belowground, but slower than buried leaf litter. There was no evidence that reduced sunlight exposure beneath plant cover affected litter mass remaining over time. Our study provides insight into the ecosystem services of cover crops, particularly their role in the first step of carbon turnover of crop litter. Identifying additional benefits of cover crops in highly intensified agroecosystems of the Pampas underscores their potential to balance high productivity with sustainable practices that support healthy biogeochemical cycles.