Late Summer Planted Oat-Brassica Forage Quality and Change during Winter

The change in nutritive value of late summer planted oats and brassicas during the winter is not well documented. Over a two-year study, samples were collected at fifteen random locations within four 12 ha paddocks in early November, December, and January near Clay Center, Nebraska. Oats (Avena sativa) were clipped at ground level and purple top turnip (Brassica rapa) and daikon oilseed radish (Raphanus sativus) tops were separated from their roots. These forages were planted on September 8^th and August 25^th in yr 1 and 2, respectively. The year by date by species interaction was not significant (P > 0.20) for either in vitro organic matter digestibility (IVOMD) or CP. There were year by species and date by species interactions (P < 0.01) for IVOMD, with oats having lesser IVOMD in yr 2 (69%) than yr 1 (80%), but IVOMD of turnip (87%) and radish top (86%) not differing (P ≥ 0.25) among year within species. In each month, the turnip and radish tops did not differ (P ≥ 0.09) in digestibility and were more (P < 0.01) digestible than oats. Within species, the digestibility in November and December did not differ (P ≥ 0.17) but decreased (P < 0.01) from December to January. However, the digestibility of oats appeared to decline more (9% units) than turnip and radish tops (5% units). For CP, the date by species interaction was not significant (P = 0.26), but there were (P < 0.01) year by date and year by species interactions. The CP content of oats (21% yr 1 and 10% yr 2) was lesser (P < 0.01) than radish and turnip top in both years. The CP of the radish (29%) and turnip (28%) top did not differ (P = 0.27) in yr 1, but in yr 2 the CP of radish top (24%) was greater (P < 0.01) than turnip top (20%). The CP content decreased (P < 0.01) 2 to 3% units from November to December in both years, but in yr 1, CP content increased (P < 0.01) 4% units from December to January, whereas, CP continued to decrease (P < 0.01) 2% units from December to January in yr 2. Although the forage changed color from green to brown after hard freezes in November, the forage retained much of its nutritive value through January.