Minimum‐Tillage Forage Turnip and Rape Production on Hill Land as Influenced by Sod Suppression and Fertilizer 1

Insufficient herbage during the fall in the temperate areas of the world has long been a serious limitation in animal production. The purpose of this research was to determine the feasibility of producing Brassica spp. forage crops for fall grazing of sheep on hill land. The experiment was conducted near Waynesburg, Pa., in a 4‐ha hill pasture, predominantly Dormont silt loam (fine‐loamy, mixed, mesic Ultic Hapludalf) on the sideslopes and Culleoka loam (fine‐loamy, mixed, mesic Ultic Hapludalf) on the ridge. A split‐plot block arrangement was used with blocks of ‘Sirius’ turnip, ( Brassica rapa L.) ‘Fora’ rape, ( B. napus L.), and ‘Perko P.V.H.’ winter rape ( B. rapa L.) randomized in each of six blocks. Competition from the existing species was suppressed with paraquat (l,l′‐dimethyl‐4,4′‐bipyridinium ion) or glyphosphate [isopropylamine salt of N ‐(phosphonomethyl)glycine] at 1.1 kg a.i. ha −1 . Nitrogen and P fertilizer treatments were assigned to subplots in a randomized complete block design. Fertilizer was applied before seeding in 1978 and 1979 to provide 0, 33, 66, 99, or 132 kg N ha −1 and 0, 15, 30, 45, or 60 kg P ha −1 in a 5 2 factorial arrangement. The crops were minimumtillage (min‐till) planted on 10 Aug. 1978 and 25 July 1979. Dry matter (DM) yields were determined 60 and 90 days after planting. Select samples were taken to determine crude protein, in vitro dry matter disappearance (IVDMD), and mineral element composition. Mean crop yields were similar for the two herbicide treatments in 1978 but were − 35 to 75% higher on glyphosate‐treated plots than on paraquat‐treated plots in 1979. Grass yield in the Brassica plots in 1979 were twice as high in the paraquat‐treated plots as in the glyphosate‐treated plots. At the higher rates of applied N and P, DM yield exceeded 7000 kg ha −1 in 1978 and 9000 kg ha −1 in 1979. Crop yield responses were quadratic functions for N fertilizer rates and linear functions for P fertilizer rates for both harvests in 1978. In 1979, yield responses were linear functions for N fertilizer rates for both harvests and for P fertilizer rates for the 60‐day harvest; and were quadratic for P rates for the 90‐day harvest. Yield of turnip and rape was affected more by P fertilizer before the 60‐day harvest than afterwards. Crude protein concentration ranged from 60 to 250 g kg −1 . Nitrogen and P fertilizers differentially affected the crude protein concentration of forage turnip and rapes. Mean IVDMD was 950 and 900 g kg −1 for turnip tops and roots, respectively, 910 g kg −1 for Fora rape, and 930 g kg −1 for Perko rape. Yield of digestible DM of turnip was up to 67% higher than that of stockpiled orchardgrass. The Brassica spp. had different DM mineral element compositions, and concentrations of P, K, Ca, Mg, and Zn generally were higher in Brassica spp. than in orchardgrass checks.