PLANTING DATE AND SEEDING RATE EFFECTS ON MORPHOLOGICAL DEVELOPMENT AND YIELD OF TURNIP

Productivity of Kentucky bluegrass (Pea pratensis L.) pastures in midw estern and northeastern USA typically is low in late fall. A study was conducted to determine the influence of planting date and seeding rat e on morphological development of turnip (Brassica rapa L.), and its p otential to provide forage in late fall. Turnip was seeded in rows on Hagerstown silt loam (fine mixed, mesic Typic Hapludalf soil, utilizin g a split-split block design with replicates nested within each whole block (planting date). Cultivar and seeding rate combinations were ran domized within each replicate, and sampling date was the split split b lock. Total yield of turnip sometimes exceeded 10.0 t ha(-1). With Jun e or July plantings, turnip had 500 to 800 g kg(-1) in its tops 60 d a fter planting, whereas with August plantings it had 700 to 900 g kg(-1 ) in its tops. In December, the proportion in tops ranged from 250 g k g(-1) for 'Purple Top' to 650 g kg(-1) for 'Tyfon' planted in June or July; and from 500 g kg(-1) for Purple Top to 850 g kg(-1) for Tyfon p lanted in August. The proportion of total yield that remained until mi d-December varied with planting date, cultivar, and foliar disease sev erity. Yield of tops or roots of five turnip cultivars differed in 36 of 38 planting date/sampling date combinations. Seeding rates within t he range 1.7 to 5.0 kg ha(-1) generally did not affect root yields. Me an crude protein concentration ranged from 270 g kg(-1) in 'Forage Sta r' to 250 g kg(-1) in 'Rondo'. Crude protein yield of Forage Star rema ined unchanged throughout the 120 d period whereas crude protein yield s of 'NZ Green Globe', Rondo, and Purple Top decreased linearly and th at of Tyfon showed a quadratic response (an initial gain followed by a sharp decline). Differences in turnip yields in late autumn were attr ibuted to planting date, amount and time of summer precipitation, plan t resistance to foliar diseases, cold tolerance, and leaf retention. D elaying summer planting date affected top/root proportions of purple T op most, and those of Forage Star and Tyfon least.