Responses of Spring Oilseed Rape Seed Yield and Quality to Nitrogen and Sulfur Fertilization

Field experiments were carried out to determine the effects of nitrogen (N) and sulfur (S) fertilization on seed yield (SY) of spring oilseed rape (Brassica napus L. var. napus), crude protein (CP), crude fat (CF), glucosinolate (GSL) concentration in seed, and yield of quality components per ha (crude protein yield, CPY; crude fat yield, CFY; glucosinolate yield, GSLY). This study also determined the N and S fertilizer use efficiencies (NFUE, SUFE) to produce SY, CFY, and CPY per unit of respective fertilizer under different conditions of cultivation years. A spring rape double-low variety Maskot was grown at three rates of N fertilizer (0, 90, and 150 kg N ha(-1)) and three rates of S fertilizer (0 20, and 40 kg S ha(-1)) on an Endocalcari-Epihypogleyic Cambisol of middle Lithuanian lowland. Year (Yr) and N rate significantly (at P < 0.01) influenced all parameters tested (except for CF and GSL). The CF concentration significantly depended on N rate (at P < 0.01) and did not depend on experimental year and S rate. Conversely, the effects of the cultivation year and S rate were significant at P < 0.01 on GSL concentration. The GSL tended to increase through application of the greatest fertilizer rates: 150 kg N ha(-1) and 40 kg S ha(-1). The greatest SY (2975 kg ha(-1) on average) was produced in the moderately cool and wet year with the longest growing and seed ripening period in comparison with the rest of the study years. The maximum NFUE-s for SY and seed quality component yields were obtained in 2004 and 2005 cultivation years with N fertilizer rate 90 kg N ha(-1) when combined with 20 kg S ha(-1) S rate. The NFUEs for SY were 8.22 and 10.11 kg seed per kg N fertilizer used, respectively. Contribution of one kg of S fertilizer was very variable: from negative to twice as high values as those related to NFUE.