Cover crop effects on soils and subsequent crops in the pampas: A meta-analysis

Cover crops are a valuable management option for reducing soil erosion and nitrogen losses from agroecosystems. They improve soil quality but the impacts on crop yield depend on the type of cover crop, the commercial crop considered and the climate. In the Argentine Pampas the introduction of cover crops in rotations is being extensively studied by official institutions. We performed a meta-analysis with results of 67 local field experiments in which winter cover crop effects on soils and crops were analyzed. Soil physical properties improved after cover crops. Bulk density was minimally affected, structural stability and water infiltration increased, while soil penetration resistance decreased. Soil organic carbon content of the 0-20 cm layer rose ca. 4% in fine-textured soils and 9% in coarser ones. Nitrate-N decreased after cover crops by 30% regardless if the cover crop species was or was not legume. Soil available water at crop sowing was not affected by cover crops in the upper meter of the profile but when the cumulative water content was measured at depth (ca. 2 m) it decreased by around 20%. Soybean (Glycine max) yield was barely affected by the previous cover crop or fallow treatment. Conversely, corn (Zea mays) yield tended to decrease when the cover crop was a non-legume (- 8%) or significantly increased after legume species (+7%) when compared to a fallow. In the Pampas, cover crops have multifunctional benefits and their adoption will depend on the balance between these benefits, the sowing cost and some possible negative effects on corn yield. For this latter crop, legume cover crops are recommended.