Nitrogen and Sulfur Fertilization in Kale and Swede for Grazing

Species in the Brassicaceae family, hence forth brassicas, such as forage kale [<i>Brassica. oleracea</i> L. convar <i>acephala</i> (DC)], swede (<i>B. napus</i> L. var. <i>napobrassica</i>), turnip [<i>Brassica rapa</i> L. <i>var. rapa</i> (L.) Thell], and hybrids (<i>B. rapa</i> L. × <i>B. pekinensis</i> L. or <i>B. rapa</i> L. × <i>B. oleracea</i> L.), have become an important source of forage for grazing worldwide. One of the limitations of forage brassicas is the relatively higher water content and low forage yield in rain-fed environments. The objective of this study was to determine swede and kale forage yield and nutritive value response to various nitrogen (N) and sulfur (S) fertilization rates. The study was conducted at two experimental field sites in North Dakota in 2012 and 2014. Kale cv. Maris Kestrel and swede cv. Major Plus and five N rates (0, 50, 100, 150, and 200 kg N ha⁻¹) and two rates of S (0 and 40 kg S ha⁻¹) were evaluated. Swede total forage yield was greater than kale across all nitrogen and sulfur rates. Compared with no N fertilization, N fertilization increased total leaf and root/stems yield and nitrogen accumulation in leaves, roots, and stems. Sulfur did not affect forage yield. Forage nutritive value was greater in swede than kale due to a higher proportion of edible root compared with kale’s higher proportion of fibrous stems. Nitrogen and sulfur interacted with some forage nutritive components. This study results suggest that growers will benefit from greater forage yield in kale and swede if they fertilize with N up to 200 kg N ha⁻¹. Forage yield and nutritive value of swede and kale in the northern Great Plains are novel results, since these crops are not grown for forage and represent an interesting and valuable new alternative for beef cattle growers.