THE EFFECT OF SULFUR FERTILIZATION ON MACRONUTRIENT CONCENTRATIONS IN THE POST-HARVEST BIOMASS OF RAPESEED (BRASSICA NAPUS L. SSP OLEIFERA METZG)

Brassica oilseed crops have very high sulfur requirements. The progressive decrease in the sulfur content of soil, the growing share of cruciferous vegetables in agricultural ecosystems and a significant drop in annual wet and dry deposition of sulfur have prompted a growing body of research into sulfur as a valuable fertilizer ingredient. The aim of this study was to determine the effect of sulfur fertilizers applied to soil on nitrogen, phosphorus, potassium, calcium, magnesium and sulfur concentrations in the root residues, straw and oil cake of winter and spring rapeseed. The experimental material was collected from a field experiment conducted in 2005-2008 at the Agricultural Experiment Station in Balcyny (Poland). The highest concentrations of nitrogen, phosphorus, magnesium and sulfur were noted in the oil cake of both winter and spring rapeseed. Potassium levels were highest in the root residues of winter and spring rapeseed. Winter rapeseed accumulated the highest amounts of calcium in roots, and spring rapeseed in straw. Sulfur fertilizers applied to soil decreased nitrogen concentrations and increased calcium and sulfur levels in the roots of both spring and winter rapeseed, whereas phosphorus concentrations increased only in the roots of winter rapeseed. Sulfur fertilization led to a drop in the potassium content of winter rapeseed roots (by 0.7 g kg(-1) DM) and an increase in potassium levels in spring rapeseed roots (by 1.2 g kg(-1) DM). The application of sulfur fertilizers significantly increased potassium and sulfur concentrations in the straw of both spring and winter rapeseed (by 1.3-1.7 and 0.5-0.6 g kg(-1) DM, respectively). The application of sulfur fertilizers at optimaldoses for winter rapeseed significantly increased the calcium content of straw (by 1.3 g kg(-1) DM), but did not lead to differences in nitrogen levels. Sulfur fertilization significantly reduced nitrogen (by 0.7 g kg(-1) DM) and calcium (by 0.6 g kg(-1) DM) concentrations of spring rapeseed straw. The content of all the analyzed macronutrients increased significantly in spring rapeseed oil cake in response to sulfur fertilization. Sulfur also increased the concentrations of the evaluated macronutrients, excluding nitrogen and phosphorus, in winter rapeseed oil cake.