Influence of sulfur on apparent N-use efficiency, yield and quality of oilseed rape (Brassica napus L.) grown on a calcareous soil

In the Lorraine region, major soils used for winter oilseed rape are calcar eous. Across two pot and two field experiments, we studied the influence of sulfur applied at different levels on apparent N-use efficiency (ANU), yie ld, glucosinolate (GLS) and oil content of seeds. The soil received a const ant dose of 200 kg N ha(-1) as ammonium nitrate, urea or cow slurry and thr ee levels of S: 0, 30 and 75 kg ha(-1) as ammonium thiosulfate (ATS), MgSO4 or ATS plus MgSO4. Apparently, oilseed rape is a N-inefficient crop as rev ealed by low ANU values which varied within 36 and 53% from field experimen t versus 25 and 61% under controlled conditions. In both cases, S additions improved N-use efficiency only at the highest dose of 75 kg S ha(-1), whic h is not attained by ATS with 35 kg S ha(-1) (10% v/v). S fertilization inc reased the GLS contents that were found to be negatively correlated with pl ant N/S uptake ratios observed at maturity. The most important increase in GLS content by 52% was noted with cow slurry in the pot experiment. But, as a whole, the GLS levels remain below the European norm of 18 mu mol g seed (-1). Moreover, the oil content (% DM) of seeds decreased (but the total pr oduction increased) when the soil was fertilized with N and with or without S. The results showed that N and S nutrition during the growth were tightl y linked. Their interactions, as reflected by plant uptake, are synergistic at optimum rates and antagonistic at excessive levels of one of the both. Collectively, the results indicate that S fertilization is required to impr ove N-use efficiency and thereby maintaining a sufficient oil level and fat ty acid quality. (C) 2000 Elsevier Science B.V. All rights reserved.