Introducing grazeable cover crops to the winter wheat systems in Oklahoma

Authors: HORN, KYLE - Oklahoma State University; ROCATELI, ALEXANDRE - Oklahoma State University; WARREN, JASON - Oklahoma State University; Turner, Kenneth; ANTONANGELO, JOAO - Oklahoma State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2020
Publication Date: 6/8/2020
Citation: Horn, K.M., Rocateli, A.C., Warren, J.G., Turner, K.E., Antonangelo, J.A. 2020. Introducing grazeable cover crops to the winter wheat systems in Oklahoma. Agronomy Journal. https://doi.org/10.1002/agj2.20326. 112:3677-3694.
DOI: https://doi.org/10.1002/agj2.20326

Interpretive Summary: Winter wheat is the primary cash crop in Oklahoma with regards to acreage and economic relevance. A considerable amount of the winter wheat is grown in a continuous system where the field is planted in the fall and harvested in the late spring, then the field is left fallow without appropriate soil cover during summer. We initiated a study to assess the impact of introducing summer cover crops (warm-season grasses or legumes and mixtures) to a Southern Great Plains winter wheat system. The system was evaluated for two consecutive seasons in two contrasting locations differing in soil type and weed pressure. The canopies of the cover crops were harvested using different cutting (stubble heights) to evaluate potential of summer weed suppression. In addition, we evaluated the effect of cover crop stubble heights (uncut, severe, and proper) on subsequent season winter-wheat grain production. Cover crop mixtures (e.g. pearl millet + mungbean or sorghum sudangrass + cowpea) and monoculture grass (e.g. sorghum sudangrass) were better than monocultures legumes (e.g. forage soybean, cowpea, mungbean) during summer limited-water periods in providing high amounts of biomass and weed suppression. Uncut cover crops provided greater weed suppression than canopies managed with proper and severe cutting. Overall, summer cover crops effects on next season’s wheat grain production were negligible. But, higher wheat yields were evident from fields previously cropped with uncut cover crops than severe or proper cut in 2016 at Chickasha research site. Summer cover crops for the Southern Great Plains must be selected based on resilience to adverse rainfall patterns rather than their exceptional biomass production potential under favorable conditions. This information is useful to producers in managing winter wheat systems to minimize weedy plant invasion and improve grain production. The information is useful to researchers trying to identify drought-tolerant, short-season plants for the summer growing and to the Natural Resources Conservation Service in refining practices and guidelines relating cover crops for soil conservation improvement in the Southern Great Plains.

Technical Abstract: Fields are typically kept summer fallow after winter wheat (Triticum aestivum L.) grain harvest in the 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 eight different cover crops’ forage yield, residue cover potential, and weed suppression, and subsequent effect on next-season wheat grain production and quality. Monocultures and select mixtures of cover crops were established in late spring of 2016 and 2017 in Chickasha and Perkins, OK sites. At 6 weeks after planting (WAP), three cutting regimes based on stubble height were used: severe (2.5 cm), proper (legumes: 7.5 cm, grasses and mixtures: 15 cm), and no cutting. Cover crops regrowth was chemically terminated at 14 WAP; winter wheat was seeded into the residues; then harvested in May 2017 and 2018. Triple treat sorghum sudangrass (Sorghum bicolor x S. bicolor var. sudanese) and mixtures showed the highest available forage dry matter in 2016 and 2017, respectively. Monoculture warm-season grasses and mixtures had higher forage dry matter residue and improved weed suppression compared to monoculture legumes. Cover crops did not affect wheat production. However, all no cut cover crops increased wheat yields in Chickasha, 2016. Cover crop establishment, growth, and regrowth were impacted by erratic rainfall patterns in summer 2017; therefore, selecting short-season cover crops resilient to adverse weather conditions would be beneficial to wheat farming systems in the SGP.