Introducing grazeable cover crops to the winter wheat systems in Oklahoma

Fields are typically kept fallow after winter wheat (Triticum aestivum L.) grain harvest in the U.S. southern Great Plains (SGP). Introducing summer cover crops to the system could increase soil conservation and farm profitability if grazed. The objective of this research was to evaluate cover crops' forage yield, residue cover potential, weed suppression, and effect on wheat production. Monocultures and grass-legume mixtures of cover crops were established in mid-June of 2016 and 2017 near Chickasha and Perkins, OK. At 6 weeks after planting (WAP), three cutting regimes based on stubble height were used: severe (2.5 cm), recommended (legumes: 7.5 cm, grasses and mixtures: 15 cm), and no cutting. Cover crops regrowth was chemically terminated at 14 WAP; winter wheat was no-till seeded in mid-October; then harvested in early-June 2017 and 2018. Cultivar Triple Treat sorghum-sudangrass [Sorghum bicolor (L.) Moench x S. bicolor var. sudanese] and grass-legume mixtures showed the greatest available forage dry matter. Grasses and grass-legume mixtures had greater forage dry matter residue and weed suppression than legumes. Results indicated that exceeding 6.4 +/- 1.2 Mg ha(-1) of total dry matter (TDM) produced during the summer, a wheat grain yield penalty of -50.1 +/- 15.8 kg ha(-1) resulted for each increment of 1.0 Mg ha(-1) of TDM produced. Also, a wheat protein content penalty of -1.9 +/- 0.5 kg ha(-1) resulted in each increment of 1.0 Mg ha(-1) of TDM produced when exceeding to 5.7 +/- 1.0 Mg ha(-1) TDM threshold. Findings suggest N uptake by high-biomass grasses and mixtures might result in deficient water and N availability for wheat production.