MANAGEMENT AND ENVIRONMENT EFFECTS ON BRASSICA FORAGE QUALITY

Forage Brassica spp. have been shown to produce adequate amounts of he rbage during the cooler months of the fall, thus allowing extension of the grazing season in higher latitudes. The objective of this study w as to determine if the nutritive quality of initial and regrowth herba ge was influenced by planting and harvest date. In 1987, 1988, and 198 9, three Brassica spp. (rape [B. oleracea L.], turnip [B. rapa L.] and turnip hybrid [B. rapa L. x B. pekinensis L.]) were planted in late M ay to early June, late June to early July, and late July to early Augu st and were harvested each year at 64, 76, or 85 DAP. The plants regre w 60, 70, or 80 d and were harvested. Nutritive components measured we re CP, NDF, ADF, Ca, Mg, and P. Nutritive levels declined with warmer temperatures and low soil moisture levels particularly during July and August. Neutral-detergent fiber and ADF levels were higher, while the CP levels were lower in herbage from the earliest planting date compa red with the later planting dates, regardless of species and year. The levels of Ca, Mg, and P were influenced by species and planting date. In general, the regrowth herbage had a lower fiber and a higher prote in content than the initial herbage. The variation in nutritive qualit y among the three species was relatively small. Of more importance to the producer is that the quality of brassica herbage is more comparabl e to a concentrate than a traditional forage because of the relatively low fiber and high protein content.