Sulphur requirement of malting barley: effects on yield and quality and diagnosis of sulphur deficiency

Abstract

Eight field experiments were conducted on four sites in 2003 and 2004 to investigate the effects of sulphur (S) application on yield and malting quality of barley. Winter barley (cv Pearl) was grown at two sites in East Anglia (Docking) and southeast of England (Woburn). Spring barley (cv Optic) was grown at two sites in Scotland (Corsekelly, Aberdeenshire) and County Durham (Bishop Middleham). Sulphur was applied as gypsum at 0, 10, 20 and 40 kg S/ha, in combination with two rates of N, which differed between sites. In addition, two additional treatments tested application of S at a later timing. Leaf tissues were sampled at tillering and stem extension and determined for a number of diagnostic indicators. A selected number of grain samples were analysed for malting quality.

Significant yield responses to S additions were obtained in five out of the eight experiments conducted at four different sites in two seasons, with yield increases ranging from 0.2 to 1.2 t/ha. Depending on the experimental site, the rate of S addition to achieve the maximum yield varied between 10 and 20 kg S/ha. This project showed that S should be applied to winter barley between mid-March to mid-April. The S-responsive experiments were associated with a soil extractable S in the range of 2.8 - 4.1 mg/kg, whereas the non-responsive trials had soil extractable S in the range of 6.4 - 14 mg/kg.

None of the leaf tissue indicators predicted yield responses with 100% accuracy at either tillering or stem extension. Leaf N:S ratio and sulphate-S concentration, measured at stem extension, appeared to be quite reliable at distinguishing the two most responsive sites from the rest. Retrospectively, grain N:S ratio at 17:1 also separated the two most responsive sites from the other sites.

Sulphur had both positive and negative influences on grain and malting quality at the two S-deficient sites. Sulphur application significantly increased malt diastatic power, alpha-amylase activity, friability and homogeneity, indicating an improved endosperm modification during malting. Sulphur applications also significantly decreased beta-glucan concentration in wort, which is beneficial for beer filtration. At the two S-deficient sites, S application significantly increased the concentration of dimethylsulphide (DMS) precursor in the wort, which is expected to have an impact on the flavour of beer. When N supply was limiting, S applications decreased grain N concentration due to a dilution effect as a result of increased grain yield. However, no significant effect was observed when N was not limiting. The main negative effect of S applications was decreased grain size, with increased proportion of small grain (<2.25 mm) and decreased thousand grain weight, although this effect was not observed in every S-responsive trial. Increasing N rate also produced similar effects. As expected, at sites that were not S-deficient or were marginally deficient, S applications had little effect on grain or malting quality parameters.