Forage Dry Matter Accumulation and Quality of Turnip, Swede, Rape, Chinese Cabbage Hybrids, and Kale in the Eastern USA1

Abstract

AbstractProduction of cool‐season (C3) herbage generally is low in summer and fall in the humid eastern USA. This study was conducted to determine the yields and pest problems of spring‐sown turnip, Brassica rapaL.; swede, B. napusL.; rape, B. napusL.; interspecific crosses between Chinese cabbage, B. campestris sensufaioL., and turnip or rape; or kale, B. oleraceaL., that were stockpiled. The crops were no‐till seeded (turnip and swede at 1.4 kg ha−1, rape, the hybrids, and kale at 4.2 kg ha−1) into mature alfalfa (Medicago sativaL.)‐grass stands. Prior to seeding, the sod was treated with isopropylamine salt of N‐(phosphonomethyl) glycine at 1.1 kg a.i. ha−1. The study was made in central Pennsylvania on Hagerstown silt loam (fine, mixed, mesic Typic Hapludalfs) soil in 1979 and 1980 and on Hublersburg silt loam (clayey, illitic, mesic Typic Hapludults) soil in 1981. Dry matter yield determinations were made sequentially at 30‐day intervals from 60 to 150 days post‐seeding. Fertilizer (P and K) was applied according to soil test results and 80 kg N ha−1was applied at seeding and 70 kg N ha−1between the 60‐ and 90‐day sampling dates. Three‐year mean dry matter yields for 13 of 19 cultivars exceeded 7.0 Mg ha−190 days post‐seeding. Yields plateaued from 80 to 160 days depending on plant species, cultivar, and year. Cultivar (across species) ✕ sampling date, turnip cultivar ✕ year, and swede, rape, and kale sampling date ✕ year interactions were significant for yield. Incidence of plant diseases was positively related to slowing of growth at physiological maturity. Some New Zealand turnip and rape cultivars were more resistant to flea beetle [Phyllotreta cruciferaeGoeze and P. striolata(Fab.)] than cultivars of European origin. Crude protein concentration of turnip and Chinese cabbage hybrid tops was higher at 120 than 90 days, but it was not for other species. Crude protein concentration ranged from 110 g kg−1in roots of certain cultivars to 270 g kg−1in turnip tops. Species ✕ sampling date and year ✕ sampling date interactions were significant for crude protein concentration and in vitro dry matter disappearance (IVDMD). The IVDMD values ranged from 800 to 930 g kg−1Kale had the lowest mean IVDMD, 840 g kg−1.