Structure and water infiltration in an Ultisol affected by cover crops and seasonality

Abstract

Cover crops (CCs) are fundamental to conservation agriculture. However, the specific effect of different species and consortia of CCs on soil structure still needs to be well understood. In addition, the effect of seasonality on soil structure requires further investigation. Thus, this study aimed to report which species or consortia of CCs improve the structure and infiltration of water in the soil more broadly and whether seasonality influences the physical properties and the infiltration of water of the soil in a no-till area in southern Brazil. The experiment was conducted under a Psammentic Paleudult, involving six treatments: T1 - bare soil with maintenance of the surface crust (BS), as the control condition; T2 - permanent grasses (predominantly Paspalum notatum) (PG); T3 - black oats (Avena strigosa) + forage turnip (Raphanus sativus) in winter, followed by beans (Phaseolus vulgaris) or cowpea (Vigna unguiculata) in summer (OT/B); T4 - ryegrass (Lolium multiflorum) in winter, followed by black beans or pigeon pea (Cajanus cajan) in summer (Rg/B); T5 - black oats + vetch (Vicia villosa) in winter, followed by black beans or cowpea in summer (OV/B); and T6 - forage peanut (Arachis pintoi) (FP). In 2022, after six years of experiment (medium term), we evaluated soil bulk density and pore size distribution (0–5, 5–20, 20–40, and 40–60 cm layers), aggregate stability (0–10 cm layer), water infiltration (with double concentric ring and Cornell infiltrometer), soil moisture (continuous monitoring at a depth of 5 cm) and biomass input. Areas under the PG treatment presented high aggregate stability but decreased macroporosity (especially in 0–20 cm) and water infiltration compared to other treatments with CCs. The FP treatment provided the broadest and most evident benefits in soil structure. Treatments with annual cover crops, especially OT/B, had improvements in soil structure compared to the FP treatment. As biomass above and especially below ground level increased, physical properties improved. In summer, macroporosity was higher (in all layers) and soil moisture lower, which increased the steady infiltration rate by 377 % compared to winter. In conclusion, the species or consortia of CCs and seasonality influence the structure and infiltration of water in an Ultisol under no-till in southern Brazil, and the contribution of biomass from live plants is a major criterion to guide the choice of CCs with great capacity to conserve or regenerate the functionality of the soil structure.