Over-seeded cool-season annuals for cover crop or forage roles in warm-season perennial grass pastures

Abstract

Over-seeded annual grasses and legumes, which can provide forage on dormant perennial warm-season grass pastures, serve as cover crops on fallow cropland. Although erosion control is not a typical need for pastures with perennial grass sod, cover crops functioning as catch crops to reduce cool-season nutrient loss or legumes for N fixation could contribute to reduced-cost warm-season pasture growth. Treatments of over-seeded cool-season species and management evaluating effects of cover crop removal as forage versus mulched as a N source were evaluated at three locations in 3 years. Cool-season legumes produced more biomass N than cool-season grasses, indicating biological N contributions of the legumes. Nitrogen limitation of the less productive, non-fertilized grasses indicates that readily available soil N had been depleted, limiting N leaching. Despite mulching of legume biomass with N amounts of 45–89 kg ha⁻¹, biomass production of bermudagrass [Cynodon dactylon (L) Pers.] in the following growing season was not increased. Lack of benefit of cover crop N contributions to subsequent bermudagrass forage production indicates that the availability of increased soil N was not synchronized with periods of efficient bermudagrass N uptake. These unanticipated results appear to be due to the effect of N mineralization-immobilization processes on N availability combined with variable rates of bermudagrass growth in response to periodic moisture limitations in this warm, humid, but uncertain environment.