Sulphur nutrition index in relation to nitrogen uptake and quality of winter wheat grain

A sulphur nutrition index (SNI) is an analogue of the N nutrition index, which is a widely used simple indicator of plant N status. The aim of this study was to relate the SNI (ratio of S concentration in shoot biomass to critical S concentration - Sc) to N uptake, grain yield and breadmaking quality of winter wheat (Triticum aestivum L.) grain during 4-yr small-plot field experiments realized under non-limiting N conditions in three different locations in the Czech Republic. The model of S dilution curve (Sc) developed by Reussi et al. (2012) for spring wheat was used for expression of the SNI. According to the model, optimal S concentration in shoot biomass was calculated using nothing but shoot biomass weight. The constant value of Sc = 0.55 was determined for shoot biomass weight lower than 1.0 t ha(-1). A very strong correlation was recorded between the SNI and an N to S weight ratio (N:S) in shoot biomass. Both, optimal N:S weight ratio in shoot biomass and qualitative parameters of grain (particularly Zeleny sedimentation volume, grain protein content and wet gluten content) were recorded if the SNI exceeded values of 0.80 at the beginning of stem elongation, 0.70 at the late boot stage, and even 0.60 at the beginning of heading despite the fact that the Reussi et al.'s model of S dilution curve was originally applicable only until the end of stem elongation. Correlation between the SNI and relative grain yield was weak.