Planting Date and Seeding Rate Effects on Morphological Development and Yield of Turnip

Abstract

Productivity of Kentucky bluegrass (Poa pratensis L.) pastures in midwestern and northeastern USA typically is low in late fall. A study was conducted to determine the influence of planting date and seeding rate on morphological development of turnip (Brassica rapa L.), and its potential to provide forage in late fall. Turnip was seeded in rows on Hagerstown silt loam (fine mixed, mesic Typic Hapludalt) soil, utilizing a split‐split block design with replicates nested within each whole block (planting date). Cultivar and seeding rate combinations were randomized within each replicate, and sampling date was the split‐split block. Total yield of turnip sometimes exceeded 10.0 t ha−1. With June or July plantings, turnip had 500 to 800 g kg−1 in its tops 60 d after 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 kg−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 planted in August. The proportion of total yield that remained until mid‐December varied with planting date, cultivar, and foliar disease severity. Yield of tops or roots of five turnip cultivars differed in 36 of 38 planting date/sampling date combinations. Seeding rates within the range 1.7 to 5.0 kg ha−1 generally did not affect root yields. Mean crude protein concentration ranged from 270 g kg−1 in ‘Forage Star’ to 250 g kg−1 in ‘Rondo’. Crude protein yield of Forage Star remained unchanged throughout the 120 d period whereas crude protein yields of ‘NZ Green Globe’, Rondo, and Purple Top decreased linearly and that of Tyfon showed a quadratic response (an initial gain followed by a sharp decline). Differences in turnip yields in late autumn were attributed to planting date, amount and time of summer precipitation, plant resistance to foliar diseases, cold tolerance, and leaf retention. Delaying summer planting date affected top/root proportions of Purple Top most, and those of Forage Star and Tyfon least.