Forage rotation and tillage effects on soil physical and chemical properties

Abstract

Annual forages can be grown more intensively than grain crops, which may have negative impacts on soil health because of biomass removal. The objective of this study was to determine the effects of annual forage crop rotations of varying intensity, diversity, forage removal, and associated tillage practices on soil physical and chemical properties. A long-term forage study was conducted near Garden City, KS. The six rotation and tillage combination treatments of the study were (1) forage sorghum (Sorghum bicolor (L.) Moench)–forage sorghum (FS–FS) no-tillage (NT), (2) triticale (×Triticosecale Wittm. ex A. Camus [Secale × Triticum])/FS–FS–oat (Avena sativa L.; T/FS–FS–O) reduced till (RT), (3) T/FS-FS-O NT, (4) T/FS–FS–FS-O NT, (5) T/FS–FS–FS–O RT, and (6) T–FS–O NT. Soil samples were taken in 2021 and 2022 at depths of 0–5 cm and 5–15 cm from the experimental plots and adjacent land used for grain production in a wheat-sorghum-fallow rotation. Results of the study indicated that the less intense rotation, T-FS-O, had more water stable microaggregates, the grain control had smaller macroaggregates, and T/FS-FS-O RT had larger macroaggregates and tended to have fewer small aggregates. Similarly, diverse forage rotations like T-FS-FS-FS-O had larger sized (2.0–6.3 mm) dry aggregates and tended to have fewer smaller aggregates. The grain control had more medium sized (0.42–0.84 mm) dry aggregate than T/FS-FS-O RT. Soil total nitrogen concentrations were less for less diverse or less intense forage rotations compared with the grain control, and soil organic carbon (SOC) and P were less for all forages compared with the grain control, perhaps because forage harvesting reduced crop residue cover and organic matter cycling. We conclude that forage systems that remove biomass from the field should be integrated with management that leaves more residue on the soil surface, such as allowing forage regrowth after hay harvest, alternating between hay removal and grazing, or rotating between forage and grain crops to keep more residue on the soil surface to maintain SOC and protect the soil from erosion.