Evaluating cover crops forage nutritive value in Oklahoma winter wheat systems.

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

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2021
Publication Date: 7/18/2021
Citation: Horn, K.M., Rocateli, A.C., Warren, J.G., Turner, K.E. 2021. Evaluating cover crops forage nutritive value in Oklahoma winter wheat systems.. Agronomy Journal. 113:3361-3371.

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) for grazing to a Southern Great Plains winter wheat system. The system was evaluated for two consecutive seasons in two contrasting locations differing in soil type. The canopies of the cover crops were harvested using different cutting (stubble heights) to evaluate simulated severe, controlled grazing, or no grazing. Forage production and nutritive value data were used to simulate potential stocker beef steer weight gains. Cover crop grass alone (e.g. sorghum sudangrass) and mixtures (e.g. pearl millet + mungbean or sorghum sudangrass + cowpea) were better than legumes alone (e.g. forage soybean, cowpea, mungbean) during summer limited-water periods in providing high amounts of biomass. Legumes provided the highest nutritive value in comparison to warm-season grasses and grass-legume mixtures. Mungbeans and cowpea resulted in higher simulated daily steer gain and total steer gain per area than grasses and mixtures. Grasses and mixes with high dry matter production compensated for the associated low forage nutritive value to help maintain simulated animal performance. This information is useful to producers in managing winter wheat systems to better utilize legume cover crops to maximize stocker steer weight gains. 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 and grazing in the Southern Great Plains.

Technical Abstract: Winter wheat (Triticum aestivum L.) is a valuable crop in Southern Great Plains that grows from fall to spring; then fields are typically kept summer fallow. Adding grazeable cover crops to the summer fallow period could help increase farm profitability. The objective of this research was to evaluate eight different cover crops’ production, nutritive value, and simulated stocker calf performance. Cover crops were established late spring 2016 and 2017 in Chickasha and Perkins, OK. At 6 weeks after planting (WAP), three simulated grazing regimes based on cutting height were used: severe (SEV; 2.5 cm), proper (PRP; legumes 7.5 cm; grasses and mixtures 15 cm), and no graze. Triple treat sorghum sudan (TTSS, Sorghum bicolor x S. bicolor var. sudanese) and mixtures showed the highest available forage dry matter (AFDM) in 2016 and 2017. Legumes had the highest nutritive value in comparison to warm-season grasses and grass-legume mixtures. Of the legumes, mungbeans (Vigna radiata L.) and cowpea (Vigna unguiculata L.) resulted in higher simulated daily steer gain (DSG) and total steer gain per area (TSGA) than grasses and mixtures 6 WAP using PRP graze at the Perkins site in 2016 as a result of superior forage nutritive value, which compensated for lower forage yields. At the Chickasha site in 2016, grasses and mixes had higher TSGA than legumes despite their lower predicted DSG. Drought in 2017 affected overall results. Grasses and mixes with high ADFM production compensated for the associated low forage nutritive value to help maintain simulated animal performance.