Optimisation of sulphur fertilisation by deficiency risk assessment. I. Winter oilseed rape | Optimisation de la fumure sufree par estimation du risque de carence. I. Colza d'automne
2003
Pellet, D. | Mercier, E. | Balestra, U. (Station federale de recherches en production vegetale de Changins (RAC), Nyon (Switzerland)) | Lavanchy, J.-C. | Pfeifer, H.-R. | Keiser, A. | Bezencon, N.
The experimental results of four growing seasons (1999-2002) were analysed to improve a prediction model of sulphur deficiency for winter oilseed rape previously presented in the «DBF 2001» (Ryser et al., 2001). This scoring model based on agronomic pedologic and climatic criteria explained 85% of yield variability in response to sulphur fertilisation. In order of importance, the parameters of the model were soil depth, clay content, organic matter and plant-available nitrogen. Moreover, rainfall between October to March, stone content and frequency of organic fertiliser applications were also taken into account. The risk of deficiency was divided into 3 categories. The threshold for low risk was set at a score of 24 points and no S fertilisation was required for oilseed rape grown at low risk sites. The optimum S application of the medium risk with a score from 15 to 23 points was determined at 35 kg S/ha. The high risk of deficiency (score under 15 points) was not represented in the experiment but a proposition of fertilisation as high as 60 kg S/ha has been made. The effects of S fertilisation on total S uptake in the aerial biomass and quality of the harvested grains were also evaluated. A significant increase of total S uptake in response to S fertilisation was observed. Besides, the glucosinolates concentration in the grains also increased significantly with S application for all cases of moderate risk and for 3 out of 6 cases at low risk sites. Finally, sulphur had a positive influence on seed oil content of 4 out of 9 cases of moderate risk and no effect on the low risk sites.
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