Agronomic Studies of Forage Brassicas as Full-Season and Cover Crops for Grazing in North Dakota

Abstract

Annual forages represent a good feed resource to extend the grazing season into fall and winter, providing a good quality forage for the livestock, allowing more efficient use of rangeland, and at the same time improving soil properties. Many species in the Brassicaceae family are used as forages for grazing. Forage brassicas are characterized by high forage yield, with high nutritive value, low establishment and harvest cost (direct grazing), while providing many ecosystems services. Forage brassicas can be grown as full season forage crops or as cover crops planted after a grain crop. The objectives of this study were: 1) to identify brassicas species and cultivars with high biomass production and forage quality when grown as full-season and as cover crops in North Dakota; 2) to determine their optimum sowing date, plant density and the response to different N and S fertilization rates. Replicated experiments were conducted at four sites Fargo, Prosper, Carrington and Walcott, ND in 2012-2014. Results indicate swede (Brassica napus L. var. napobrassica) and kale [B.oleraceae L. convar. acephala (DC)] were the highest forage yielding brassicas when established in full-season and turnip [Brassica rapa L. var. rapa (L.) Thell).], cv. ‘Appin’ was the highest yielding sown after August. In full-season brassicas, delaying sowing date reduced total forage yield in all species but did not influence forage quality. In brassicas sown after August, total forage yield decreased significantly only in radish in the second sowing date. Plant density did not have an effect on forage yield or N accumulation averaged across environments and species in full-season forage brassicas. This was different in brassicas sown after August, where the highest forage yield was obtained with the highest plant density (≥200 plants m-2). Kale and swede leaf, root/stem, and dead matter yield increased up to 200 kg N ha-1 in a linear response. Sulfur and the interaction between N and S did not have an effect in forage yield and quality. Both full-season and cover crops forage brassicas have great potential as supplemental high quality forage for grazing in North Dakota.