Seasonal Variation in Chemical Composition of Forage Brassicas. I. Mineral Concentrations and Uptake

Abstract

AbstractLittle information is available on the mineral composition of summer‐ and autumn‐grown Brassica forages and the ability of these crops to provide the mineral requirements of grazing ruminants. This paper reports on seasonal variation of mineral composition and uptake in summer‐ and autumn‐grown turnip (B. rapa L.), rape (B. napus L.), swede (B. napus L.), and Tyfon [B. rapa L. ✕ B. pekinensis (Lour.) Rupr.]. Species were no‐till seeded into glyphosate [N‐(phosphonomethyl)grycine]‐suppressed sod in Connecticut on a Paxton fine sandy loam soil (coarse‐loamy, mixed, mesic Typic Dystrochrept) in 1983 and 1984. Concentrations of Ca, Mg, K, Cu, Fe, Mn, and Zn in summer‐grown species were similar to or exceeded concentrations in autumn‐grown species. Species grown during autumn, however, had greater concentrations of N and P. Foliage concentrations of Ca, Mg, N, and Mn were noticeably greater than root concentrations of the same minerals. Total mineral uptake in summer‐grown species was significantly greater for Ca, Mg, K, Cu, Fe, and Mn relative to uptake of these minerals in autumn‐grown species. Although species or seasonal effects, or species ✕ season interaction effects were significant for particular minerals, concentrations of Ca, Mg, P, K, N, and Fe were adequate or well above recommended levels for ruminants. Micromineral supplementation, however, may be needed for ruminants consuming Brassica grown on soils with low micromineral availabilities. Because of high mineral uptake, depletion of soil fertility would be rapid if native fertility is low and limited fertilizer is applied to these crops.